Ulnar Neuropathy at the Wrist - Electromyography and Neuromuscular Disorders PDF

SECTION VIII Clinical Disorders PART I Common Mononeuropathies 23 Ulnar Neuropathy at the Wrist Ulnar neuropathy at the wrist (UNW) is a rare condition that hypothenar muscles; the superficial branch containing...

SECTION VIII Clinical Disorders PART I Common Mononeuropathies 23 Ulnar Neuropathy at the Wrist Ulnar neuropathy at the wrist (UNW) is a rare condition that hypothenar muscles; the superficial branch containing sometimes is confused with ulnar neuropathy at the elbow the sensory fibers and motor innervation to the palmaris (UNE) or, more often, with early motor neuron disease. brevis is not affected. Knowledge of the detailed anatomy of the ulnar nerve at the Proximal deep palmar motor lesion: affects all ulnar-­ wrist is necessary to understand the several unique clinical and innervated hand muscles, including the hypothenar electrophysiologic patterns that can occur with UNW (Fig. muscles, with the exception of the palmaris brevis; 23.1). The differential diagnosis is limited and includes com- the superficial branch containing the sensory fibers pression both external and internal to the wrist, the latter from and motor innervation to the palmaris brevis is not various structural lesions. Accordingly, neuromuscular ultra- affected. sound plays an important adjunctive role to electrodiagnostic studies in the evaluation of these patients. Similar to other ulnar neuropathies, it is especially helpful in those cases where 'RUVDOXOQDU the electrodiagnostic study is unable to localize the ulnar neu- FXWDQHRXVVHQVRU\ ropathy and UNW remains in the differential diagnosis. 3DOPDUFXWDQHRXV VHQVRU\ 6XSHUILFLDOEUDQFK 'HHSSDOPDUPRWRU ANATOMY EUDQFK %UDQFKWRWKHSDOPDULV At the wrist, the ulnar nerve enters Guyon’s canal at the level +\SRWKHQDUPRWRU EUHYLV of the distal wrist crease. The canal is formed proximally by 'LJLWDOVHQVRU\ the pisiform bone and distally by the hook of the hamate. The floor is formed by a combination of the transverse car- pal ligament and the adjacent hamate and triquetrum bones. The roof is loosely formed. In contrast, there is a thick band at the outlet that runs from the hook of the hamate to the pisiform bone, creating the pisohamate hiatus. In the canal, the nerve divides into superficial and deep branches. Before exiting through the pisohamate hiatus, motor fibers are given 3LVLIRUP  off the deep branch (also known as the deep palmar motor ERQH branch) to three of the four hypothenar muscles (abductor digiti minimi [ADM], flexor digiti minimi, and opponens   digiti minimi). After the hiatus, the superficial branch sup- +RRN plies sensation to the volar fifth and medial fourth digits and  RIWKH KDPDWH also supplies motor innervation to the one remaining hypo- thenar muscle, the palmaris brevis. The deep palmar motor branch goes on to innervate the third and fourth lumbricals, Fig. 23.1 Detailed anatomy of the ulnar nerve at the wrist. Entrap- the four dorsal and three palmar interossei, the adductor ment of the ulnar nerve at the wrist can take on several patterns: (1) pollicis, and the deep head of the flexor pollicis brevis. pure motor affecting only the distal deep palmar motor branch, distal to the hypothenar muscles; (2) pure motor affecting the proximal deep palmar branch, including the hypothenar motor branches; (3) motor CLINICAL and sensory (proximal canal lesion); and rarely (4) sensory affecting the superficial branch involving the sensory fibers to the volar fourth Several subtypes of UNW occur, depending on the and fifth fingers. The superficial branch does supply one muscle, the exact location of the lesion and which fibers are affected palmaris brevis. This muscle, however, is difficult to assess clinically or (Table 23.1 and Box 23.1). The following lesions have been by electromyography, although there are reports of the “palmaris brevis sign” wherein this muscle is spared or prominent in lesions of the deep described: palmar motor branch (see Fig. 23.2). (Adapted with permission from Distal deep palmar motor lesion: affects all muscles Olney RK, Hanson M. AAEE case report no. 15: ulnar neuropathy at or supplied by the deep palmar motor branch except the distal to the wrist. Muscle Nerve. 1988;11:828.) 402  Chapter 23 Ulnar Neuropathy at the Wrist 403 Proximal canal lesion: affects all branches of the ulnar hand and fingers will be spared because they are innervated nerve, including the proximal and distal deep palmar by the dorsal ulnar cutaneous sensory branch, which arises motor and the superficial branches that contain the sen- several centimeters proximal to the wrist. This is an impor- sory fibers and motor innervation to the palmaris brevis. tant clinical point to remember when trying to discern if Superficial branch lesion: affects only the superficial the ulnar nerve lesion is at the wrist or more proximal. In branch, which is primarily sensory. Note that while the addition, the proximal volar medial hand should be spared palmaris brevis muscle is affected, this is not clinically because the palmar cutaneous branch also arises just proxi- apparent. mal to the wrist.    The first two patterns are the most common, accounting for more than 75% of all cases of UNW. In both, the superfi- Box 23.1 Clinical and Electrophysiologic Abnormalities Not Consistent With Ulnar Neuropathy cial branch is not affected; thus, there are no sensory symp- at the Wrist toms or sensory loss. Patients present with painless weakness and atrophy of ulnar intrinsic hand muscles. Because the Clinical ulnar-­innervated adductor pollicis and deep head of the flexor W eakness of thumb abduction (abductor pollicis brevis— median innervated) pollicis brevis are in the thenar eminence, both the hypothe- Weakness of the distal finger flexors of digits 4 and 5 (flexor nar and thenar eminences may be wasted, if the lesion is in digitorum profundus—ulnar innervated in the forearm) the proximal deep palmar motor branch. Similar to UNE, the Weakness of index finger extension (extensor indicis Benediction hand posture, Froment’s sign, and Wartenberg’s proprius—radial innervated) sign may be present in advanced cases. In addition, another Sensory symptoms/signs in the dorsal medial hand/ somewhat obscure sign, known as the “palmaris brevis sign,” dorsal fifth and fourth fingers (territory of the dorsal ulnar cutaneous sensory branch) may be seen in severe lesions of the deep palmar motor Sensory symptoms/signs in the medial forearm (territory of branch. Remember that the palmar brevis is the only muscle the medial antebrachial cutaneous sensory nerve) supplied by the superficial branch and is therefore spared in lesions of the deep branch. When the palmaris brevis con- Nerve Conduction Studies tracts, it results in puckering of the skin along the proximal A bnormal median motor study (unless there is a coexistent carpal tunnel syndrome) medial border of the hand. Because the other intrinsic hand Abnormal dorsal ulnar cutaneous sensory study muscles are wasted, prominent contraction (and possibly Focal slowing or conduction block of the ulnar nerve at the hypertrophy) of the palmaris brevis may be seen when the elbow fifth digit is forcibly contracted in the more common lesions of the deep palmar motor branch of the ulnar nerve at the Needle Electromyography wrist (the “palmaris brevis sign,” Fig. 23.2). A bnormalities in the proximal ulnar-­innervated muscles (flexor carpi ulnaris and flexor digitorum profundus to digits 4 and 5) In more proximal lesions, the superficial branch will also Abnormalities in non-­ulnar C8-­innervated muscles (abductor be affected, leading to sensory disturbance of the volar fifth pollicis brevis, flexor pollicis brevis, extensor indicis proprius) and medial fourth digits. The dorsal medial aspect of the Table 23.1 Clinical and Electrophysiologic Differentiating Factors in Variants of Ulnar Neuropathy at the Wrist. Deep Palmar Motor Deep Palmar Motor Proximal Superficial Branch Distal Branch Proximal Canal Brancha Weakness—interossei and 3rd/4th lumbricals X X X Weakness—hypothenar muscles (ADM, ODM, FDM) X X Sensory loss—volar medial hand and little finger, X X medial half ring finger Reduced CMAP at FDI X X X Reduced CMAP at ADM X X Prolonged FDI latency X X X Prolonged ADM latency X X Reduced SNAP to digit 5 X X Prolonged latency comparing INT to 2nd LUM X X X Conduction block at the wrist X X X CV slowing at the wrist X X X EMG abnormalities in FDI X X X EMG abnormalities in ADM X X    aThe superficial branch is often thought of as a “sensory branch.” However, it does supply one muscle, the palmaris brevis. ADM, Abductor digiti minimi; CMAP, compound muscle action potential; CV, conduction velocity; EMG, electromyelography; FDM, flexor digiti minimi; INT, interossei; LUM, lumbrical; ODM, opponens digiti minimi; SNAP, sensory nerve action potential; X, abnormalities may be present. 404 SECTION VIII   Clinical Disorders ETIOLOGY is especially true for bikers or laborers who use the same hand tools repetitively, which results in pressure on the Entrapment of the ulnar nerve at the wrist is far less com- hypothenar eminence (Fig. 23.4). In such patients, the mon than at the more usual sites at the elbow. It has been hypothenar area may be callused at the compression site. described in association with trauma and wrist fracture. However, more common is a ganglion cyst within Guyon’s canal that compresses the ulnar nerve (Fig. 23.3). Rarely, DIFFERENTIAL DIAGNOSIS an anomalous muscle or other mass lesions have been In lesions where the superficial branch containing the sensory reported, including ulnar artery aneurysms, lipomas, and fibers is not affected, UNW is most often confused with early other tumors. In addition, certain occupations or activi- motor neuron disease. Motor neuron disease is well known to ties that involve repetitive movement or pressure against present with painless atrophy and weakness of a distal limb, the ulnar wrist predispose to lesions at this location. This a pattern essentially identical to distal UNW lesions. The key differentiating finding on physical examination in UNW is the intact strength and bulk of the abductor pollicis brevis muscle, supplied by the median nerve. In motor neuron disease, one would expect all C8–T1-­innervated muscles supplied by dif- ferent peripheral nerves to be affected. In UNW, there is a marked difference between ulnar C8–T1-­innervated muscles (which are weak and wasted) and median C8–T1-­innervated muscles (which are spared). However, this difference in ulnar versus median innervated muscles can also be seen in some atypical motor neuron disorders, such as multifocal motor neuropathy with conduction block, a rare autoimmune medi- ated motor neuropathy that preferentially affects distal mus- cles in a non-myotomal pattern of weakness (see Chapter 29). In proximal lesions at the wrist where the superficial Fig. 23.2 Palmaris brevis sign. When the palmaris brevis contracts, it branch (and hence sensory fibers) is affected, the differential results in puckering of the skin along the proximal medial border of diagnosis is similar to that of UNE. Indeed, in UNW with sen- the hand. Because the palmar brevis is the only muscle supplied by sory involvement, the most important diagnosis to exclude is the superficial branch of the ulnar nerve at the wrist, it will be spared UNE. Unequivocal sensory loss over the medial dorsal aspect in lesions of the deep branch. Thus, prominent contraction of the pal- of the hand and fingers and/or weakness of the distal flexors maris brevis may be seen when trying to abduct digit 5 in the more common lesions of the deep palmar motor branch of the ulnar nerve of the ring and little fingers are consistent with a lesion at the at the wrist. Note the prominent contraction of the palmaris brevis elbow, not at the wrist. However, in mild or early cases of and wrinkling of the skin on the right hand (arrows) compared to the UNE, these signs may not be present. In addition to UNE, normal left hand. (Adapted with permission from Iyer VG. Palmaris one must keep in mind the possibilities of C8–T1 radiculopa- brevis sign in ulnar neuropathy. Muscle Nerve. 1998;21:675–677.) thy, lower trunk or medial cord brachial plexopathy, and rare 1st Metacarpal Cyst Hamate Pisiform Cyst Fig. 23.3 Ganglion cyst in Guyon’s canal. One of the more common causes of ulnar neuropathy at the wrist is compression of the ulnar nerve by a ganglion cyst. Computed tomographic scan of the wrist. Left, Axial scan, volar side up. Note the cyst medial to the hook of the hamate. Right, Coronal scan, lateral hand up. Note the cyst between the pisiform and the hamate. (From Preston DC, Shapiro BE, Schecht HM. Ganglion cyst at Guyon’s canal: electrophysiology and pathology. J Clin Neuromusc Dis. 2001;3:89–91.)  Chapter 23 Ulnar Neuropathy at the Wrist 405 Box 23.2 Recommended Nerve Conduction Study Protocol for Ulnar Neuropathy at the Wrist Routine studies: The following patterns denote ulnar neuropathy at the wrist with 1. Ulnar motor study recording the abductor digiti minimi, certainty: stimulating the wrist, below groove, and above groove in the DML to FDI in the demyelinating range: >130% upper limit flexed elbow position of normal (i.e., any DML to the FDI >6.0 ms) 2. Ulnar motor study recording the first dorsal interosseous, Focal slowing across the wrist during inching studies: ≥0.5 ms stimulating the wrist, below groove, and above groove in over a 1-­cm increment, recording FDI the flexed elbow position Conduction block, comparing palm and wrist stimulations, 3. Ulnar motor study recording the first dorsal interosseous, recording FDI stimulating the wrist (3 cm proximal to the distal wrist Conduction velocity slowing across the wrist, recording FDI crease) and palm (4 cm distal to the distal wrist crease) Special considerations: 4. Median motor study recording the abductor pollicis brevis, If the superficial sensory branch is affected, the SNAP stimulating the wrist and antecubital fossa amplitude will be low or absent, with a normal dorsal ulnar 5. Median and ulnar F responses cutaneous SNAP. (Caution must be taken in interpreting this 6. Ulnar sensory response, recording digit 5, stimulating wrist pattern, which also can occur in patients with UNE.) (bilateral studies) Occasional false-­positive results occur when using the 7. Median sensory response, recording digit 2 or 3, stimulating DML to FDI or ADM; comparing DML to FDI versus ADM; wrist and the lumbrical-­interossei study, especially in cases of 8. Dorsal ulnar cutaneous sensory response (bilateral studies) moderate or severe UNE with axonal loss. Wrist versus Additional studies to consider: palmar stimulation studies, or inching studies across the 9. Ulnar motor study recording the contralateral first dorsal wrist should be done to demonstrate UNW with certainty. interosseous, stimulating the wrist (to compare distal If the dorsal ulnar cutaneous sensory study is performed and latencies and amplitudes side to side) is absent, it is prudent to stimulate the superficial radial sensory 10. Lumbrical-­interossei distal latency comparison study nerve along the lateral radius with the recording electrodes 11. Ulnar motor study recording the first dorsal interosseous, in place for the dorsal ulnar cutaneous sensory study to ensure inching across the wrist in 1-­cm increments that an anomalous innervation is not present (recall there is The following patterns are consistent with ulnar neuropathy at a very rare anomalous innervation wherein the superficial radial the wrist: sensory nerve supplies the entire dorsum of the hand, including DML to FDI: >4.5 ms (provided CMAP amplitude is not the usual territory of the dorsal ulnar cutaneous sensory nerve). markedly reduced) DML comparing FDI to ADM: >2.0-ms difference DML comparing symptomatic FDI to contralateral FDI: >1.3 ms difference DML comparing ulnar INT to second lumbrical: >0.4 ms difference ADM, Abductor digiti minimi; CMAP, compound muscle action potential; DML, distal motor latency; FDI, first dorsal interosseous; INT, interossei; SNAP, sensory nerve action potential; UNE, ulnar neuropathy at the elbow; UNW, ulnar neuropathy at the wrist. cases of ulnar nerve entrapment in the arm or forearm, which (FDI). In lesions of the distal deep palmar motor branch, can present with similar symptoms and signs. the latency to the FDI may be prolonged with a decreased compound muscle action potential (CMAP) amplitude. ELECTROPHYSIOLOGIC Comparison with the contralateral asymptomatic side often is helpful as well. In cases where the lesion is more EVALUATION proximal, affecting the hypothenar branches, the distal Nerve Conduction Studies motor latency (DML) to the ADM also may be prolonged, The findings on nerve conduction studies in UNW depend on with a decreased CMAP amplitude. However, one of the (1) whether the superficial sensory branch is involved and (2) patterns highly suggestive of UNW is preferential involve- if the deep motor branch is involved, whether it is affected ment of the distal deep palmar motor branch, whereby the proximal or distal to the hypothenar muscles. If the lesion is ulnar motor study recording the FDI is affected out of pro- distal, affecting only the deep palmar motor branch after the portion to the ulnar motor study recording the ADM. Com- take-­off to the hypothenar muscles, then the routine ulnar parison of their relative distal motor latencies often can be sensory study, recording the fifth digit, and the routine ulnar helpful. motor conduction study, recording the ADM, will be normal. In suspected UNW, additional nerve conduction studies must always be performed to detect abnormalities that may not be present on routine ulnar motor and sensory studies (Box 23.2). Normal Values In addition to routine ulnar motor studies recording DML to FDI ≤4.5 ms ADM and sensory studies recording digit 5, the following DML comparing FDI to ADM ≤2.0 ms difference studies often are helpful. DML comparing symptomatic FDI ≤1.3 ms difference Ulnar Motor Studies Recording the First Dorsal to contralateral FDI Interosseous ADM, Abductor digiti minimi; DML, distal motor latency; FDI, first dorsal interosseous. In all cases of suspected UNW, it is imperative to perform ulnar motor studies recording the first dorsal interosseous 406 SECTION VIII   Clinical Disorders sensory study in the context of an abnormal digit 5 ulnar sensory study certainly suggests a diagnosis of UNW, this is not always the case. This pattern does not necessarily exclude the possibility of UNE (see Chapter 22). In some patients with definite UNE with axonal loss (although usu- ally mild), the dorsal ulnar cutaneous sensory potential is spared. This is thought to be due to preferential fascicular sparing of the dorsal ulnar cutaneous sensory fibers. There- fore care must be taken when interpreting the findings of a patient with a normal dorsal ulnar cutaneous SNAP and an abnormal digit 5 ulnar sensory response, especially if there is no conduction block or focal conduction velocity slow- ing across the elbow. These findings must be interpreted in light of findings on the ulnar motor studies and the needle electromyographic (EMG) study. Only when the dorsal ulnar cutaneous sensory study is abnormal is one assured that the lesion is above the level of the wrist; the converse is not always true. Median Second Lumbrical Versus Ulnar Interossei Distal Motor Latencies The lumbrical-­interossei distal latency comparison often is performed as a sensitive, internal comparison study to dem- onstrate median nerve slowing across the carpal tunnel (see Chapter 20, Fig. 20.10). However, this study can be used just as effectively to demonstrate UNW (Fig. 23.5), look- Fig. 23.4 Occupational and activity risk factors for ulnar neuropa- ing for significant slowing of ulnar compared with median thy at the wrist. Occupations that require repetitive use of hand tools fibers across the wrist. Because the interossei are innervated can result in pressure on the hypothenar eminence (upper arrow). In by the distal deep palmar motor branch of the ulnar nerve addition, certain activities, especially prolonged cycling, can similarly result in ulnar neuropathy at the wrist (bottom arrow). and the second lumbrical is innervated by the median nerve, this comparison test can be very useful in identifying ulnar slowing at the wrist. A DML difference of greater than 0.4 ms comparing the ulnar interossei with the median second Dorsal Ulnar Cutaneous Sensory Study lumbrical, stimulating the nerves at the same distance, sug- In cases of suspected UNW where the routine ulnar sensory gests focal slowing of the ulnar nerve across the wrist. conduction to digit 5 is abnormal, it is important to study This study is reliable and easy to perform. However, two the dorsal ulnar cutaneous sensory nerve. As the dorsal ulnar limitations must be kept in mind. First, if an ulnar neuropa- cutaneous sensory nerve arises 5–8 cm proximal to the wrist, thy has a moderate or severe amount of axonal loss, be it at it is expected to be normal in all cases of UNW. A normal the wrist or higher, one should expect some mild slowing antidromic response is greater than 8 μV, but, as in other across the wrist simply on the basis of loss of some of the uncommonly performed sensory nerve conduction studies, fastest conducting axons. Second, the lumbrical-­interossei comparison with the contralateral asymptomatic side fre- study will fail in cases of UNW if there is a coexistent quently is helpful. Any potential that is less than 50% of the median neuropathy at the wrist. This is generally not an amplitude of the contralateral asymptomatic side likely is issue when using this comparison study for median neuropa- abnormal as well, even if the absolute amplitude is greater thy at the wrist, as UNW is so rare. However, when looking than 8 μV.1 for a UNW, an incidental median neuropathy at the wrist Although the dorsal ulnar cutaneous sensory study often may not be that uncommon. is helpful in establishing the level of the lesion, there are significant limitations of which every electromyographer Short Segment Incremental Studies must be aware. Although a normal dorsal ulnar cutaneous Using a technique identical to that used for ulnar nerve lesions at the elbow, short segment incremental studies, or “inching,” 1Very rarely, there is an anomalous innervation wherein the superficial can be effectively performed at the wrist, recording the FDI, radial sensory nerve supplies the entire dorsum of the hand, including looking for an abrupt change in either latency or amplitude the usual territory of the dorsal ulnar cutaneous sensory nerve. Thus, (Fig. 23.6). One-­centimeter increments are carefully marked in cases where the dorsal ulnar cutaneous sensory response is absent, off from 2–4 cm above the distal wrist crease to 4–5 cm below. it is prudent to stimulate the superficial radial sensory nerve along the The ulnar nerve is then stimulated supramaximally at each lateral radius, with the recording electrodes in place for the dorsal ulnar location at successive 1-­cm intervals, from below to above cutaneous sensory study, to ensure that this very rare anomalous inner- vation is not present (see Chapter 7, Fig. 7.14). the wrist. Any abrupt increase in latency or drop in amplitude  Chapter 23 Ulnar Neuropathy at the Wrist 407 P9 * PV Fig. 23.5 Lumbrical-­interossei comparison study. This study is used most often in the diagnosis of carpal tunnel 6WLPXODWH0HGLDQ syndrome but can be equally helpful in the diagnosis of * ulnar neuropathy at the wrist. The median nerve is stimu- 5HFRUG/ lated at the wrist (S1), while the second lumbrical muscle is recorded (right top trace); the ulnar nerve is stimulated at the wrist (S2), using the same distance, while the 6WLPXODWH8OQDU interossei muscles are recorded (right bottom trace). In 6 5HFRUG,17 normal controls, latencies are similar. In a patient with 6 ulnar neuropathy at the wrist, the interossei latency is /XPEULFDO,QWHURVVHL&RPSDULVRQ6WXG\ prolonged compared with the second lumbrical. P9' PV'    ':&     Fig. 23.6 Short segment incremental study of the   ulnar nerve across the wrist. Left, Recording the first  dorsal interosseous, the ulnar nerve is stimulated in ':&  successive 1-­cm increments across the wrist. Right,   Note the abrupt increase in amplitude, shift in latency,   and change in morphology of the compound muscle action potential between 2 and 3 cm distal to the distal wrist crease (DWC). Inching studies allow for exact  localization of the lesion. (From Preston DC, Shapiro BE, Schecht HM. Ganglion cyst at Guyon’s canal: elec- trophysiology and pathology. J Clin Neuromusc Dis. ,QFKLQJ$FURVVWKH:ULVW 2001;3:89–91.) between successive stimulation sites implies focal demyelin- localizing the lesion. However, additional information is also ation. In normal individuals, the latency between two succes- gained about prognosis, as demyelinating lesions have a far bet- sive 1-­cm stimulation sites usually is 0.1–0.3 ms and rarely 0.4 ter prognosis than those associated with axonal loss. ms. Any latency shift ≥0.5 ms suggests focal slowing. Comparison of the Various Electrophysiologic Tests in Wrist and Palmar Stimulation Ulnar Neuropathy at the Wrist Comparing the CMAP amplitudes stimulating at the wrist and There has been little data comparing the relative useful- palm can be technically easier than inching across the wrist and ness of the various studies outlined earlier, because UNW yields similar information (Fig. 23.7). To perform this study, is relatively uncommon. Most reports of UNW have been the ulnar nerve is stimulated 3 cm above the wrist and 4 cm single case reports or reports of a small number of patients. distal to the distal wrist crease in the palm, recording the FDI. One large study of 20 consecutive patients with clinically Whereas inching requires multiple stimulations at 1-­cm incre- defined UNW was performed prospectively, comparing the ments, this study only requires single palm and wrist stimula- following studies: (1) wrist and palmar stimulation stud- tions. UNW can be localized either by finding a conduction ies, recording FDI, looking for conduction block across the block between the wrist and palm stimulation sites or by find- wrist; (2) wrist and palmar stimulation studies, recording ing conduction velocity slowing across the wrist. Similar to all FDI, looking for conduction velocity slowing across the routine motor studies, if a nerve is stimulated at two sites, a wrist; (3) lumbrical-­interossei study, comparing ulnar versus conduction velocity can be calculated. In UNW, any conduction median distal latencies; and (4) routine ulnar motor studies, velocity less than 37 m/s is considered abnormal and is of local- recording FDI and ADM, comparing their respective DMLs. izing value. In UNW, the demonstration of conduction block In five patients, inching studies across the wrist also were or conduction velocity slowing is most helpful in definitively performed. Importantly, these studies were also compared 408 SECTION VIII   Clinical Disorders P9 PV $PSOLWXGH P9 :ULVW Fig. 23.7 Wrist and palm stimulation in ulnar neuropa- thy at the wrist. As an alternative to inching studies, a compound muscle action potential can be recorded at the first dorsal interosseous with stimulation at the wrist &9 PV $PSOLWXGH P9 and palm, looking for conduction block and/or conduc- tion velocity slowing across the ulnar wrist. Note that in ':& this case of ulnar neuropathy at the wrist (UNW), there 3DOP is a large decrease in amplitude with stimulation at the wrist compared to the palm, signifying conduction block and a slowed conduction velocity. Both findings localize the ulnar neuropathy to the wrist. CV, Conduc- tion velocity; DWC, distal wrist crease. :ULVWDQG3DOP6WLPXODWLRQLQ81: in 30 asymptomatic normal control subjects and in 20 con- slowing across the wrist can be demonstrated in 95% of secutive disease control patients with definite UNE. patients with clinically definite UNW. This finding was The most sensitive and specific studies for localizing the 100% specific; it was not seen in any control patient lesion to the wrist were conduction block across the wrist and with UNE. a slowed wrist-­to-­palm conduction velocity recording the FDI. 2. Inching studies across the wrist also are very sensitive Conduction block was found in 70% and a slowed wrist-­to-­ and specific. However, these studies are more time-­ palm conduction velocity in 80% of patients with UNW, using consuming and technically demanding than simply wrist and palmar stimulation (Fig. 23.8). Overall, 95% of the stimulating at one additional site in the palm. patients with UNW had either conduction block or a slowed 3. The lumbrical-­interossei study is a sensitive and helpful conduction velocity. These findings were 100% specific. Nei- test, with one important exception. Its usefulness ther conduction block nor conduction velocity slowing across is greatly diminished if there is a coexistent median the wrist was found in any of the control patients with UNE. neuropathy at the wrist. Rarely, a false-­positive result can Of the five patients in whom inching was performed, all occur if a patient has a severe UNE. Increasing the cutoff showed focal slowing and conduction block. value to 0.7 ms or above may eliminate this problem. The lumbrical-­interossei comparison study had a sensitiv- 4. Prolongation of the DML to FDI or ADM is much less ity of 60% (Fig. 23.9). However, one patient with a severe sensitive than conduction block or slowing across the UNE had an abnormal study (latency difference of 0.6 ms). wrist, recording the FDI. In addition, it is also much One reason for the lower than expected sensitivity for this less specific, being present in some cases of UNE. study was the presence of coexistent median neuropathy at 5. Comparing the DML to FDI versus ADM is only the wrist in 25% of patients. infrequently helpful, being fairly insensitive to UNW. A prolonged DML to the FDI or ADM also had a lower sensitivity, in the range of 55%–60% (Fig. 23.9). More Electromyographic Approach importantly, prolonged distal latencies to these muscles The needle EMG examination in suspected UNW is straight- were also less specific than the previously described studies. forward (Box 23.3). The FDI and ADM must be sampled, A prolonged DML to the FDI was found in one patient with with the electromyographer looking for involvement of the mild UNE and in 40% of patients with severe UNE. Simi- distal and proximal deep palmar motor branches, respec- larly, a prolonged DML to the ADM was found in 40% of tively. The flexor digitorum profundus (FDP) 5 and flexor patients with severe UNE. The prolonged DMLs in patients carpi ulnaris (FCU) must be sampled to exclude an ulnar with UNE presumably were the result of axonal loss and neuropathy proximal to the wrist. Finally, median-­and dropout of some of the faster conducting fibers. radial-­innervated C8 muscles (e.g., abductor pollicis bre- The least sensitive study for UNW was the comparison vis, flexor pollicis longus, extensor indicis proprius) and of DMLs to the FDI versus ADM, being abnormal in only the lower cervical paraspinal muscles must be sampled to 15% of patients with UNW. However, one patient with a exclude a cervical root or motor neuron lesion. mild UNE also had a relatively prolonged DML to FDI com- As in UNE, the lesion in UNW can be purely axonal, indi- pared with ADM. cated by low CMAP amplitudes at ADM and FDI with nor- The important points to take away from this study are as mal or only mild slowing of distal latency. In these cases, it follows:    can be difficult to differentiate a lesion of the deep palmar 1. By performing an additional stimulation at the palm, motor branch from a lesion proximal to the dorsal root gan- while recording the FDI, conduction block or focal glion (cervical root or motor neuron). The EMG is helpful  Chapter 23 Ulnar Neuropathy at the Wrist 409 )',&RQGXFWLRQ%ORFN  3DOP:ULVW$PSOLWXGH 3DOP$PSOLWXGH         1RUPDO    Fig. 23.8 Conduction block and focal slowing 1RUPDO 81: 81(²0LOG 81(²6HYHUH across the wrist. Top, Change in first dorsal interosseous (FDI) compound muscle action 3DOPWR:ULVW&RQGXFWLRQ9HORFLW\ potential (CMAP) amplitude with the ulnar nerve stimulated above and below the wrist is  plotted for normals, patients with ulnar neu-  ropathy at the wrist (UNW), and patients with  ulnar neuropathy at the elbow (UNE) (mild   and severe). Conduction block is calculated as  follows: (palmar CMAP amplitude minus wrist  CMAP amplitude) / palmar CMAP amplitude. 0HWHUV6HFRQG  Bottom, Conduction velocity across the ulnar   wrist, recording the FDI, is plotted for normals, 1RUPDO patients with UNW, and patients with UNE   (mild and severe). Normal limits are shown  as dotted lines. (From Cowdery SR, Preston  DC, Herrmann DN, et al. Electrodiagnosis   of ulnar neuropathy at the wrist: conduction  block versus traditional tests. Neurology. 1RUPDO 81: 81(²0LOG 81(²6HYHUH 2002;59:420–427.) )','LVWDO/DWHQF\ ,QWHURVVHRXV/XPEULFDO/DWHQF\         0LOOLVHFRQGV 0LOOLVHFRQGV     1RUPDO  1RUPDO       1RUPDO 81: 81(²0LOG 81(²6HYHUH  1RUPDO 81: 81(²0LOG 81(²6HYHUH  $'0'LVWDO/DWHQF\   Fig. 23.9 Distal motor latency studies in ulnar neuropathy at the wrist (UNW). Distal motor latencies to the first dorsal interosseous  0LOOLVHFRQGV (top left), difference in distal motor latencies between the interos-  seous and lumbrical (top right), and distal motor latencies to the abductor digiti minimi (bottom left) are plotted for normals, patients  1RUPDO with UNW, and patients with ulnar neuropathy at the elbow (UNE)  (mild and severe). Normal limits are shown as dotted lines. Note  the false-­positive results that occur in some cases of UNE. FDI, First dorsal interosseous. (From Cowdery SR, Preston DC, Herrmann DN,  et al. Electrodiagnosis of ulnar neuropathy at the wrist: conduction 1RUPDO 81: 81(²0LOG 81(²6HYHUH block versus traditional tests. Neurology. 2002;59:420–427.) 410 SECTION VIII   Clinical Disorders Box 23.3 Recommended Electromyographic Protocol for Ulnar Neuropathy at the Wrist Routine studies: 1. Distal deep palmar motor ulnar-­innervated muscle (first dorsal interosseous) 2. Proximal deep palmar motor ulnar-­innervated branches to hypothenar muscles (abductor digiti minimi) 3. Forearm ulnar-­innervated muscles (flexor carpi ulnaris and flexor digitorum profundus 5) If any of the ulnar-­innervated muscles are abnormal, test the following additional muscles: 4. At least two non-­ulnar lower trunk/C8-­innervated muscles (e.g., abductor pollicis brevis, flexor pollicis longus, extensor indicis proprius) to exclude a lower trunk brachial plexopathy, polyneuropathy, C8–T1 radiculopathy, or motor neuron disease 5. C8 and T1 paraspinal muscles Fig. 23.10 Ulnar nerve at the wrist. Top, Short axis, ulnar nerve at Special consideration: If the pathology at the wrist is purely the wrist, native image. Bottom, Same image, with the ulnar nerve in axonal and spares sensory fibers, it is difficult to completely yellow, ulnar artery in red, and pisiform bone in green. At the wrist, exclude a lesion proximal to the dorsal root ganglion (i.e., the ulnar nerve is located between the ulnar artery and the pisiform root or motor neuron). bone. superficial and deep branches. The deep branch then moves in this regard. The electromyographer can confirm that the medially while the superficial branch remains lateral, adja- abnormalities are limited to ulnar-­innervated muscles distal cent to the hook of the hamate. The ulnar artery also divides to the wrist by also sampling proximal ulnar-­innervated and to follow the two branches of the nerve. non-­ulnar C8–T1-­innervated muscles. Again, however, early External compression, such as from repetitive use of hand motor neuron disease may be difficult to exclude. In these tools or in bikers, can result in an enlarged ulnar nerve (Fig. cases, the clinical presentation and serial follow-­up remain 23.12). However, more importantly, there are several struc- important. tural abnormalities to specifically look for when assessing the ulnar nerve at the wrist. The most common is a ganglion or synovial cyst (Fig. 23.13). These cysts most frequently arise ULTRASOUND CORRELATIONS from the nearby pisiform-­triquetral joint, although they have As noted earlier, UNW is very uncommon and has a lim- been reported to arise from other carpal joints and tendon ited differential diagnosis that includes compression both sheaths. They often form a “dumbbell” shape within Guyon’s external and internal to the wrist, the latter from various canal, which compresses the ulnar nerve. structural lesions. Accordingly, neuromuscular ultrasound As the ulnar nerve runs with the ulnar artery, rare cases plays an important role in the evaluation of these patients. of thrombosis or aneurysm of the ulnar artery can occur, Similar to other ulnar neuropathies, it is especially helpful which affect the ulnar nerve in the wrist, either from direct in those cases where the electrodiagnostic study is unable compression or ischemia. to localize the ulnar neuropathy and UNW remains in the Similar to the reverse palmaris longus for the median nerve, differential diagnosis. the ulnar nerve at the wrist can also be affected by anomalous To visualize the ulnar nerve at the wrist, the probe is muscles. The most common is an accessory ADM (Fig. 23.14). placed in short axis over the median nerve at the distal wrist This muscle may originate from different forearm structures crease at the standard starting median nerve location. Once but most often arises from the forearm superficial fascia and the median nerve is identified, the probe is slowly moved the distal tendon of the palmaris longus. It runs anterior to toward the ulnar side of the wrist looking for a prominent the ulnar nerve and artery in Guyon’s canal to insert on the hypoechoic structure, which is the ulnar artery. This can pisiform bone near the origin of the ADM. In some cases, it be confirmed by color or power Doppler. Once the ulnar continues as a muscle in the palm to insert on the base of the artery is identified, the probe is very slowly moved toward proximal fifth phalanx. Note that the presence of this muscle the distal wrist. The pisiform bone will then appear on the on ultrasound may be incidental. Only when it is large can it ulnar side of the wrist. It is easily identified by its well-­ result in compression of the ulnar nerve at the wrist. demarcated bone shadow. The ulnar nerve at this loca- Although uncommon, arthritis and bony abnormali- tion (the entrance to Guyon’s canal) is found between the ties can affect the ulnar nerve in the wrist. Arthritis of the ulnar artery and the pisiform bone (Fig. 23.10). Its cross-­ pisotriquetral joint can affect the nerve. Bony callus from sectional area should then be measured while inspecting for remote fracture or bone fragments from a recent fracture any nearby structural lesions. The floor of Guyon’s canal can affect the ulnar nerve near or at the wrist (Fig. 23.15). is the transverse carpal ligament with the roof formed by This includes fracture of the hook of the hamate. Bone is the superficial palmar carpal ligament (Fig. 23.11). Mov- easily recognized on ultrasound by its hyperechogenicity ing slightly distally into the palm, the nerve divides into its and posterior acoustic shadowing.  Chapter 23 Ulnar Neuropathy at the Wrist 411 0 $ 8 3L VLI RU P $ 0 6 ' +DPDWH Fig. 23.11 Normal cross-sectional anatomy at the wrist. Axial magnetic resonance images. Top, Level at the entrance to Guyon’s canal. Bot- tom, Level at the exit from Guyon’s canal. Left, Native images. Right, Same images with the ulnar nerve in yellow with a U, superficial branch of the ulnar nerve in yellow with an S, deep branch of the ulnar nerve in yellow with a D, median nerve in yellow with an M, ulnar artery in red, transverse carpal ligament in purple, superficial palmar carpal ligament in light blue, and the pisiform and hamate bones in green. Fig. 23.12 Ulnar neuropathy at the wrist from external compression. Left, Native images. Right, Same images with the ulnar nerve in yellow, ulnar artery in red, and pisiform bone in green. Top, Short axis at the ulnar wrist. Bottom, Long axis. Note the marked enlargement of the ulnar nerve. 412 SECTION VIII   Clinical Disorders    /RQJD[LV Fig. 23.13 Ulnar neuropathy at the wrist from compression from a ganglion cyst. Top left, Short axis native image at the ulnar wrist. Top right, Short axis slightly distal to the ulnar wrist, native image. Middle, Same images with the ulnar nerve in yellow, ulnar artery in red, ganglion cyst in purple, pisiform bone edge in green, and posterior acoustic shadowing in light blue. Note that the images at the wrist are normal, but slightly distal is a large anechoic oval mass that is displacing the ulnar nerve and artery. The posterior acoustic enhancement is a common ultrasound feature that helps to identify cystic lesions. Bottom left, Native image, long axis slightly distal to the ulnar wrist. Bottom right, Same image with color flow Doppler. Note the large anechoic oval mass with posterior acoustic enhancement that is displacing the ulnar artery above.  Chapter 23 Ulnar Neuropathy at the Wrist 413 3/7 $) 8$ 81 $+ $'0 Fig. 23.14 Ulnar nerve and an accessory abductor digiti minimi (AADM). Two different individuals with an AADM muscle. Top, Left and Mid- dle, Short axis at the ulnar wrist, native images. Bottom, Left and Middle, Same images with the ulnar nerve in yellow, ulnar artery in bright red, ulnar vein in blue, pisiform bone in green, and an AADM in dark red. Right, Anatomic dissection of the hand. The pisiform bone is marked by an asterisk. ADM, Abductor digiti minimi muscle; AF, antebrachial fascia; AH and red arrow, accessory head of abductor digiti minimi mus- cle; PLT, palmaris longus tendon muscle; UA, ulnar artery; UN, ulnar nerve. (Anatomic dissection adapted with permission from Ballesteros LE, Ramirez LM. Possible implications of an accessory abductor digiti minimi muscle: a case report. J Brach Plex Periph Nerve Inj. 2007;2:22. https://doi.org/10.1186/1749-­7221-­2-­22.) Fig. 23.15 Ulnar neuropathy near the wrist from a bone fragment. Left, Short axis images just proximal to the ulnar wrist, native images, successive images moving from distal (top) to proximal (bottom). Right, Same images with the ulnar nerve in yellow, ulnar artery in red, and the bone in green. Note that a bone fragment projects up (middle image) and deforms the ulnar nerve. Ulnar neuropathy near the wrist can occur from bone fragments from the distal ulna or carpal bones proper. 414 SECTION VIII   Clinical Disorders digits 4 and 5 were strong. There was no Tinel’s sign at EXAMPLE CASE the elbow. Sensation to pin and light touch was normal. Case 23.1 Summary History and Physical Examination The history and physical examination both are suggestive A 36-­year-­old right-­handed man complained of numbness of ulnar neuropathy. Despite the normal sensory examina- and paresthesias over digits 4 and 5 and right arm pain tion, the patient noted paresthesias and numbness in the for 6 months. The sensory disturbance had become worse ulnar-­innervated fourth and fifth digits. In addition, the over the past few weeks. He worked in a library stacking motor examination showed atrophy and weakness of the books and denied any history of trauma. He had vague right ADM and the interossei. Thus the patient has clear complaints of right elbow pain. symptoms of ulnar sensory and motor dysfunction. The On examination, there was mild atrophy of the intrin- suggestion of pain at the right elbow leads one to seriously sic hand muscles. There was mild weakness of the ADM consider the possibility of ulnar neuropathy in the region and interossei muscles on the right. The long flexors of of the elbow. However, at this point, there are no other CASE 23.1 Nerve Conduction Studies Amplitude Motor = mV; Conduction F-­wave Sensory = μV Latency (ms) Velocity (m/s) Latency (ms) Nerve Stimulation Recording Stimulated Site Site RT LT NL RT LT NL RT LT NL RT LT NL Median (m) Wrist APB 12.5 ≥4 4.2 ≤4.4 28 ≤31 Median (m) Antecubital fossa APB 12.2 8.3 50 ≥49 Ulnar (m) Wrist ADM 4.2 ≥6 4.1 ≤3.3 31 ≤32 Ulnar (m) Below elbow ADM 4.1 7.4 60 ≥49 Ulnar (m) Above elbow ADM 4.1 9.2 57 ≥49 Median (s) Wrist Index finger 48 ≥20 3.2 ≤3.5 58 ≥50 Ulnar (s) Wrist Little finger 10 23 ≥17 3.4 3.2 ≤3.1 42 52 ≥50    Note: All sensory and mixed latencies are peak latencies. All sensory and mixed-­nerve conduction velocities are calculated using onset latencies. The reported F-­wave latency represents the minimum F-­wave latency. ADM, Abductor digiti minimi; APB, abductor pollicis brevis; LT, left; m, motor study; NL, normal; RT, right; s, sensory study. CASE 23.1 Additional Nerve Conduction Studies Amplitude Motor = mV; Conduction F-­wave Sensory = μV Latency (ms) Velocity (m/s) Latency (ms) Nerve Stimulation Stimulated Site Recording Site RT LT NL RT LT NL RT LT NL RT LT NL Dorsal Lateral wrist Dorsal medial 24 26 ≥8 2.1 2.2 ≤2.8 50 51 ≥50 ulnar (s) hand Median (m) Wrist Second lumbrical 4.1 3.8 ≥1.0 4.4 4.4 Ulnar (m) Wrist Interosseous 5.5 6.2 ≥2.5 5.5 4.4 Lum-­int diff. 1.1 0.0 ≤0.4 Ulnar (m) Wrist FDI 3.6 11 ≥7 5.2 4.4 ≤4.5 Ulnar (m) Below elbow FDI 3.4 7.6 55 ≥50 Ulnar (m) Above elbow FDI 3.4 8.9 57 ≥50 Ulnar (m) Palm FDI 8.0 3.2 35 ≥50    FDI, First dorsal interosseous; LT, left; m, motor study; NL, normal; RT, right; s, sensory study.  Chapter 23 Ulnar Neuropathy at the Wrist 415 CASE 23.1 Electromyography Spontaneous Activity Voluntary Motor Unit Action Potentials Configuration Insertional Fibrillation Fasciculation Muscle Activity Potentials Potentials Activation Recruitment Duration Amplitude Polyphasia Right FDI ↑ +1 0 NL ↓ +1 +1 +1 Right ADM ↑ +1 0 NL ↓ +1 +1 +1 Right APB NL 0 0 NL NL NL NL NL Right EIP NL 0 0 NL NL NL NL NL Right FCU NL 0 0 NL NL NL NL NL Right FDP 5 NL 0 0 NL NL NL NL NL    ↑ = Increased; ↓ = slightly reduced; ADM, abductor digiti minimi; APB, abductor pollicis brevis; EIP, extensor indicis proprius; FCU, flexor carpi ulnaris; FDI, first dorsal interosseous; FDP, flexor digitorum profundus; NL, normal. signs to help localize the lesion. The fact that the long What Is the Significance of the Prolonged Ulnar flexors to digits 4 and 5 (ulnar portion of the FDP) are DML? normal suggests that the ulnar neuropathy either is mild The only unusual abnormality is the moderately prolonged and has not affected these more proximal muscles or is distal latency to the ADM muscle (4.1 ms). This value is more distal. more than 125% of the upper limit of normal and sug- The clinical approach to this case is similar to that gests the possibility of a demyelinating lesion at the wrist. used in other cases of ulnar nerve dysfunction. The dif- Recall from the history that the patient uses his hands to ferential diagnosis includes UNW, UNE, lower trunk/ stack books repetitively, which may be a risk factor for medial cord lesions of the brachial plexus, or a C8–T1 entrapment of the ulnar nerve at the wrist. Further stud- radiculopathy. ies of the ulnar nerve at the wrist are indicated. The nerve conduction studies include, first, a normal median motor conduction study recording the abduc- What Other Tests Can Be Used to Help Localize the tor pollicis brevis muscle. However, the ulnar motor Lesion? conduction study shows a mildly low CMAP ampli- Because the routine ulnar conduction studies typically are tude recording the ADM with a moderately prolonged normal or equivocal in UNW, additional nerve conduction distal latency but a normal conduction velocity in the studies are required to localize the lesion to the wrist (see forearm and across-­elbow segments. There is no con- Box 23.2). In UNW, the dorsal ulnar cutaneous sensory duction block or significant differential slowing of the response is expected to be normal, whereas the sensory ulnar nerve across the elbow (>10–11 m/s) to substan- potential to the fifth digit may be abnormal. When the tiate the possibility of UNE. Median and ulnar rou- dorsal ulnar cutaneous sensory response is checked and tine sensory studies are then performed. The median compared with the contralateral side, it is normal and sym- study is completely normal, but the ulnar study shows a metric bilaterally. The presence of a normal dorsal ulnar decreased amplitude on the right with a normal ampli- cutaneous response with an abnormal digit 5 ulnar response tude on the left. Therefore, at this point in the study, is consistent with UNW, although, as already noted, this one can be fairly certain that the patient has an ulnar pattern occasionally can be seen in mild cases of UNE. neuropathy because both the ulnar motor and sensory Next, the lumbrical-­ interossei comparison study is studies are abnormal. The normal median motor and performed using identical distances. On the left (asymp- sensory studies exclude a more generalized process tomatic) side, an identical distal latency of 4.4 ms to both such as a polyneuropathy to explain the abnormal ulnar the lumbrical and interossei is found. On the involved motor and sensory findings. Although a lower trunk right side, however, there is a clear asymmetry: the ulnar brachial plexopathy is still a consideration, one would latency is 1.1 ms longer than the median latency. Any dif- expect to also see a low median CMAP amplitude in ference of more than 0.4 ms suggests focal slowing across this case. At this point in the study, we are confronted the wrist. with a common problem, that of a nonlocalizable ulnar Lastly, the ulnar motor study is repeated but recording neuropathy. There is no focal slowing or conduction the FDI. There is no focal slowing or conduction block block to suggest an UNE. across the elbow. However, the FDI distal latency on the Several questions should be addressed. involved right side is moderately prolonged at 5.2 ms, with a normal value of 4.4 ms on the contralateral side. In addition, the CMAP amplitude is reduced on the right 416 SECTION VIII   Clinical Disorders compared with the left. Comparing the distal latency to In this case, sensory symptoms and abnormalities on the FDI to that of the ADM, there is a difference of 1.1 nerve conduction studies indicated an ulnar nerve lesion. ms, which is in the range of normal (≤2.0 ms). When an However, one should remember that in other cases of additional stimulation is given in the palm while record- UNW, in which the lesion affects the deep palmar motor ing the FDI, the amplitude markedly increases to 8.0 branch in isolation, only the motor fibers are affected; the mV, signifying a conduction block between the palm and sensory fibers are spared. In such cases, excluding a lesion wrist. In addition, the calculated velocity across the wrist proximal to the dorsal root ganglion (either nerve root or is in the demyelinating range, being less than 37 m/s. anterior horn cell) may be very difficult. If the pathology is Proceeding to the needle EMG study, particular atten- axonal loss alone and there is no focal slowing or conduction tion must be paid to the ulnar-­innervated muscles above the block of ulnar motor fibers across the wrist, making that dif- level of the wrist, which would be expected to be normal ferentiation is impossible. In those unusual cases, the EMG in cases of UNW. The EMG study shows active denerva- report must be considered indeterminate. Although EMG tion and reinnervation in the FDI (innervated by the distal abnormalities may be limited to ulnar-­innervated muscles, deep palmar motor branch of the ulnar nerve). The right the possibility that those muscles are the first to be affected ADM yields similar findings, indicating that the branch to in a lesion of the nerve root or anterior horn cells cannot the hypothenar muscles is also affected. The right abduc- be completely excluded. Indeed, there are cases of focal tor pollicis brevis is normal, as is the right extensor indicis motor neuron disease that mimic UNW on initial presenta- proprius. The normal findings in these two non-­ulnar C8-­ tion, preferentially affecting the deep palmar motor branch. innervated muscles again signify that the problem likely In those cases, clinical history and often follow-­up electro- is limited to the ulnar nerve. Finally, both proximal ulnar physiologic studies are required to make the differentiation. muscles, the FCU and FDP 5, are sampled and are normal. Therefore, with EMG and nerve conduction studies completed, we are ready to form an electrophysiologic Suggested Readings impression. Bakke JL, Wolff HG. Occupational pressure neuritis of the deep palmar branch of the ulnar nerve. Arch Neurol IMPRESSION: There is electrophysiologic evidence of Psychiatry. 1948;60:549. Cowdery SR, Preston DC, Herrmann DN, et al. a right ulnar neuropathy at the wrist. Electrodiagnosis of ulnar neuropathy at the wrist: conduction block versus traditional tests. Neurology. From the pattern of the nerve conduction and EMG 2002;59:420–427. data, we can conclude that the patient has an ulnar nerve Eckman PB, Perlstein G, Altrocchi PH. Ulnar neuropathy in lesion at the wrist affecting the superficial sensory branch bicycle riders. Arch Neurol. 1975;32:130. and the proximal deep palmar branch. This pattern is one Hunt JR. Occupation neuritis of deep palmar branch of ulnar variant of UNW. In this case, the patient’s history, exami- nerve: well defined clinical type of professional palsy of nation, and electrophysiologic results all correlate well. hand. J Nerv Ment Dis. 1908;35:673. The atrophy and weakness of the intrinsic hand muscles Iyer VG. Palmaris brevis sign in ulnar neuropathy. Muscle correlate with the reduced ulnar CMAP amplitudes seen Nerve. 1998;21:675–677. on nerve conduction studies and with the denervation Kothari MJ, Preston DC, Logigian EL. Lumbrical and interossei recordings localize ulnar neuropathy at the wrist. and reinnervation with reduced recruitment of MUAPs Muscle Nerve. 1996;19:170–174. revealed by the needle EMG findings. The findings that, McIntosh KA, Preston DC, Logigian EL. Short segment taken together, tend to localize the lesion at the wrist incremental studies to localize ulnar entrapments at the include not only the EMG abnormalities that are limited wrist. Neurology. 1998;50:303–306. to ulnar muscles distal to the wrist but also the intact dor- Moneim MS. Ulnar nerve compression at the wrist: ulnar sal ulnar cutaneous sensory response and the prolonged tunnel syndrome. Hand Clin. 1992;8:337. ulnar latency on the lumbrical-­interossei study. However, Olney RK, Hanson M. AAEE case report no. 15: ulnar the study that unequivocally localizes the ulnar neuropathy neuropathy at or distal to the wrist. Muscle Nerve. to the wrist is the palmar stimulation compared to the wrist 1988;11:828. stimulation, while recording the FDI. The finding of focal Parra S, Orenga JV, Ghinea AD, Estarelles MJ, Masoliver A, Barreda I, et al. Neurophysiological study of the radial nerve demyelination across the wrist (conduction block and/or variant in the innervation of the dorsomedial surface of the conduction velocity slowing) is the key finding. hand. Muscle Nerve. 2018;58(5):732–735. One can easily see that if additional studies had not Raynor EM, Shefner JM, Preston DC, et al. Sensory and been performed (i.e., the dorsal ulnar cutaneous sensory mixed nerve conduction studies in the evaluation of ulnar study, motor conduction study to the FDI including palmar neuropathy at the elbow. Muscle Nerve. 1994;17:785. stimulation, and lumbrical-­interossei distal latency com- Shea JD, McClain EJ. Ulnar-­nerve compression syndrome at parison study), the erroneous diagnosis of a nonlocalizable and below the wrist. J Bone Joint Surg Am. 1969;51:1095. ulnar neuropathy might have been made. The initial clue Wu JS, Morris JD, Hogan GR. Ulnar neuropathy at the wrist: to this diagnosis on the nerve conduction studies was the case report and review of the literature. Arch Phys Med relatively prolonged distal latency to the ADM muscle in Rehabil. 1985;66:785. conjunction with only a mildly reduced CMAP amplitude.  SECTION VIII Clinical Disorders PART I Common Mononeuropathies Radial Neuropathy 24 In the electromyography (EMG) laboratory, the radial & nerve is studied less frequently than the median and ulnar nerves and their respective well-­known lesions. Neverthe- & less, entrapment of the radial nerve does occur, often affect- 8SSHUPLGGOHORZHUWUXQNV ing the main radial nerve either in the upper arm or axilla. & Isolated lesions of its terminal divisions in the forearm, the & posterior interosseous, and superficial radial sensory nerves, 3RVWHULRUFRUG also occur. Although radial motor nerve conduction studies 7 are technically demanding, the electrophysiologic evaluation 5DGLDOQHUYH of radial neuropathy usually is able to localize the lesion, assess the underlying pathophysiology, and provide useful information regarding severity and subsequent prognosis. In addition, similar to other entrapment neuropathies, neuro- muscular ultrasound is often very useful in adding specific anatomic information regarding the location and etiology of a radial neuropathy. ANATOMY The radial nerve receives innervation from all three trunks of the brachial plexus and, correspondingly, a contribu- tion from each of the C5–T1 nerve roots (Figs. 24.1 and Fig. 24.1 Anatomy of the radial nerve. The radial nerve receives 24.2). After each trunk divides into an anterior and poste- innervation from all three trunks of the brachial plexus and, cor- rior division, the posterior divisions from all three trunks respondingly, a contribution from each of the C5–T1 nerve roots. unite to form the posterior cord. The posterior cord gives off (Adapted with permission from Haymaker W, Woodhall B. Peripheral the axillary, thoracodorsal, and subscapular nerves before Nerve Injuries. Philadelphia, PA: WB Saunders; 1953.) becoming the radial nerve. In the high arm, the radial nerve first gives off the posterior cutaneous nerve of the arm, the then given off to the brachioradialis and the long head of lower lateral cutaneous nerve of the arm, and the posterior the extensor carpi radialis. The radial nerve then enters cutaneous nerve of the forearm (Fig. 24.3), followed by the radial tunnel, which is the space formed posteriorly by muscular branches to the three heads of the triceps bra- the distal humerus and radiocapitellar joint, the brachialis chii (medial, long, and lateral) and the anconeus. In some muscle medially, the brachioradialis muscle anteriorly, and patients, there is evidence that the long head of the triceps the extensor carpi radialis brevis muscle laterally. The radial may be supplied either by the axillary nerve or the posterior tunnel is approximately 5 cm in length and runs between cord directly. The anconeus is a small muscle in the proxi- the area where the radial nerve pierces the lateral intermus- mal forearm that effectively is an extension of the medial cular septum to where the deep motor branch enters the head of the triceps brachii. After giving off these muscu- proximal edge of the supinator.a Next, 3–4 cm distal to the lar branches, the radial nerve wraps around the posterior lateral epicondyle, the radial nerve bifurcates into two sepa- humerus in the spiral groove. The posterior cutaneous nerve rate nerves: one superficial and the other deep. The super- of the forearm accompanies the radial nerve through the spi- ficial branch, known as the superficial radial sensory nerve, ral groove and remains in the posterior compartment of the descends distally under the brachioradialis in the forearm arm before becoming subcutaneous approximately 6–7 cm and eventually moves subcutaneous over the radial bone to directly proximal to the lateral epicondyle. Descending into supply sensation over the lateral dorsum of the hand as well the region of the elbow, the main radial nerve then pierces the lateral intermuscular septum to run between the bra- aSome consider the radial tunnel to continue to where the posterior chialis and brachioradialis muscles. Muscular branches are interosseous nerve leaves the distal border of the supinator. 417