Lower Motor Neuron (LMN) and Upper Motor Neuron (UMN) Lesions PDF

Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 1 of 13 Dr. Jean Peduzzi Nelson Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Lecture Objectives I. Understand the characteristics of upper motor neurons and lower motor neurons (LMNs) and...

Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 1 of 13 Dr. Jean Peduzzi Nelson Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Lecture Objectives I. Understand the characteristics of upper motor neurons and lower motor neurons (LMNs) and their pathways. II. Compare the differences in signs of UMN and LMN lesions. III. Gain better understanding of UMN and LMN lesion by alternating hemiplegia and spinal hemisection Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 2 of 13 Dr. Jean Peduzzi Nelson I. Functional Organization of UMNSandLMNs and pathways (Fig.1) UMN and LMN are distinct systems. Upper motor neurons (pyramidal tract) consists of the neuronal cell bodies in primary motor cortex. The inferolateral part of the precentral gyrus (primary motor cortex) and innervates the nuclei of cranial nerves via corticobubar tract. Other parts of precentral gyrus contain neuronal cell bodies that innervate motor neurons in the ventral horn of the spinal cord via the corticospinal pathway. Lower motor neurons innervate muscles (Final Common Pathway of Sherrington). LMN cell bodies are located in the nuclei of cranial nerves nerve V, VII, IX, X, XI and XII and ventral horn motor neurons of the spinal cord. Important to know location and function of cranial nerves to help localize lesions. Two types of motor neurons in brainstem cranial nerve nuclei and spinal cord: a and g. a are large, multipolar neurons with prominent Nissl bodies and an axon that innervates extrafusal motor fibers. g have small, multipolar cell bodies with fine Nissl bodies and an axon that innervates the polar regions of the muscle spindle (when activated, it causes stretch of the intrafusal fibers and discharge of annulospiral fibers). Fig. 1  Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 3 of 13 Dr. Jean Peduzzi Nelson II. Signs of UMN and LMN lesions and cranial nerve lesions due to UMN and/or LMN lesion. Lesions of LMN Symptoms. Destruction of LMNs from injury (e.g., trauma) or disease (e.g., poliomyelitis) causes the “LMN syndrome”, characterized by: 1) Flaccid (flabby muscles) paralysis. Fig. 2 2) Hypotonia or atonia depends on severity of lesion. 3) Hyporeflexia (e.g., decreased DTRs) or areflexia (absence of reflexes). Fig. 2 4) Muscle atrophy and eventually reduction of muscle mass. 5) Fasciculations (random contractions of single motor units prior to muscle degeneration). https://video.search.yahoo.com/yhs/search;_ylt=AwrEZ7nBTwVigXUAZgwPxQt.;_ylu=Y29sbwNiZ jEEcG9zAzEEdnRpZAMEc2VjA3Nj?p=muscle+fasciculation+video&type=Y139_F155_204989_0 62121&hsimp=yhs-001&hspart=trp&ei=UTF-8&fr=yhs-trp- 001#action=view&id=17&vid=62799bb171ca210457fb07566dd3c4ba Lesions of UMN Symptoms. 1) Increased Deep Tendon Reflexes (DTRs) 2) Loss of superficial reflexes Cremasteric: normal reflex in males that is elicited when the inner part of the thigh is stroked. Stroking of the skin causes the cremaster muscle to contract and pull up the ipsilateral testicle Abdominal Reflexes: normally stroking the skin of the abdomen causes the underlying abdominal wall muscle to contract, pulling the umbilicus towards the stimulus 3) Clonus is a self-sustained, oscillating stretch reflex induced when the clinician briskly stretches a hyperreflexic muscle causing rhythmic series of muscle contractions https://www.youtube.com/watch?v=UX75k8s5QUE 4) Spastic Paralysis (begins few days after injury) 5) Hypertonia: increased muscle tone 6) Clasp Knife Response is a rapid decrease in resistance when attempting to flex a joint. https://www.youtube.com/watch?v=8xxe2WWWoYI 7) Babinski Sign usually begins hours or days after injury. This is tested by stroking lateral sole of the foot then the toes flair and big toe moves up. It is normal to see positive Babinski before an infant begins to walk. 8) Hoffman sign (finger flexor reflex) Tapping the nail or flicking the end of 3rd or 4th finger, positive sign is the flexion and adduction of the end of the thumb.  Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 4 of 13 Dr. Jean Peduzzi Nelson Signs of UMN Damage Signs of LMN Damage Increased Deep Tendon Reflexes (DTR) Decreased Reflexes Loss of Cremasteric & Abdominal Reflexes Muscle Fasciculation Clonus Muscle Atrophy Spastic Paralysis Flaccid Paralysis Hypertonia Hypotonia Clasp Knife Response Babinski Sign Hoffman sign III. UMN and LMN lesion by alternating hemiplegia and spinal hemisection Oculomotor Nuclear Complex (Motor nuclei of CN III) (Figure 1) V-shaped structure next to midline of rostral midbrain. Capping rostral pole is the Edinger-Westphal nucleus. Axons course through midbrain tegmentum and exit at interpeduncular fossa. Unilateral III lesion: ipsilateral ptosis, lat. strabismus (diplopia), dilated pupil (mydriasis), loss of direct light reflex and ipsilateral accommodation. Unilateral III + PT lesion (at rostral midbrain): All of the above + PT syndrome. This combo is called the superior alternating hemiplegia (aka Weber’s syndrome). Because at this level the corticobulbar tract is included in the lesion, the patient has contralateral lower facial paralysis. (Fig. 3) Superior alternating hemiplegia (Weber’s syndrome: CN III & PT tract Fig. 3 External  Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 5 of 13 Dr. Jean Peduzzi Nelson Trochlear nucleus (Motor nucleus of CN IV) Small, round nucleus ventral to periaqueductal gray at level of caudal midbrain. Axons course dorsally, cross the midline, exit at midbrain/pons transition, and ultimately innervate the sup oblique muscle which intorts the eye. Unilateral 4th nerve lesion: causes ipsilateral extortion (eyeball slightly up and out) and diplopia. Patient compensates by tilting head to the non-paralyzed side (which rotates the nonparalyzed eye). Trigeminal Motor Nucleus (Motor nucleus of CN V) Large, round nucleus located just medial to the chief sensory nucleus of V at mid pontine levels. Axons from motor V leave the pons with the Vth nerve and then its mandibular (V3) division. Innervate the ipsilateral muscles of mastication, tensor tympani and tensor veli palatini. Unilateral nerve V lesion. Results in paralysis of ipsilateral muscles of mastication with jaw deviating to paralyzed side upon protrusion. Hyperacusis may occur from paralysis of the tensor tympani. Sensory loses to the ipsilateral face are prominent but discussed elsewhere. Unilateral nerve V + PT (trigeminal alternating hemiplegia). This lesion combines the above signs + PT syndrome signs. It may occur from a single lesion occurring in the basilar portion of the pons at mid pontine levels. No facial paralysis occurs (Fig. 4) Trigeminal alternating hemiplegia: CN V & Pyramidal tract CN V Fig. 4 Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 6 of 13 Dr. Jean Peduzzi Nelson Abducens nucleus (Motor nucleus of CN VI) Fairly large, round nucleus close to midline of caudal pons. Fibers of internal genu of VII wrap around this nucleus. Axons from motor VI course ventrally in the tegmentum and exit at the junction of pons and medulla (inf pontine sulcus). Unilateral nerve VI lesion. Results in ipsilateral medial strabismus with diplopia. Unilateral abducens motor nucleus lesion. Produces the “lateral gaze syndrome”. In this syndrome, neither eye can be turned towards the lesion side and both eyes tend to be conjugately deviated to the side opposite the lesion. Unilateral nerve VI + PT lesion (middle alternating hemiplegia). This lesion can occur at the basilar portion of the caudal pons. Signs and symptoms are those of unilateral VI lesion together with the PT syndrome. Facial paralysis does not occur because the corticobulbar fibers to motor VII do not travel with PT at this level. Fig. 5 Middle Alternating Hemiplegia (Foville syndrome):CN VI and Pyramidal tract Fig. 5 Facial nucleus (Motor nucleus CN VII) Motor VII. Large nucleus in the caudal pontine tegmentum at the same level as the abducens motor nucleus. Axons from motor VII first course dorsomedial, then wrap around the abducens nucleus (internal genu), then course ventrolaterally between the spinal nucleus of V and the facial motor nucleus, finally axons exit the pons at the cerebellopontine angle, just medial to nerve VIII. Motor VII can be roughly divided into a dorsal ½ (neurons innervate upper face muscles) and a ventral ½ (neurons innervate lower face muscles). Stapedius muscle also innervated. Unilateral nerve VII lesion. Results in Bell’s palsy with patient unable to smile, show the teeth, close the eyelid, or wrinkle the forehead on the paralyzed (entire ipsilateral) side. Hyperacusis may result from paralysis of the stapedius. Ipsilateral corneal reflex is also abolished. Bell’s palsy is fairly common and must be distinguished from damage to UMN supplying the facial nucleus where only lower face is affected. Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 7 of 13 Dr. Jean Peduzzi Nelson Unilateral lesion of corticobulbar fibers innervating motor VII. Results in contralateral lower facial paralysis (patient can wrinkle forehead on both sides but cannot smile contralateral to lesion side). Unilateral VI + VII + PT. Produces the Millard-Gubler syndrome (Fig. 6) Millard-Gubler: CN VI & VII & PT Fig. 6 Nucleus Ambiguus (Fig. 7) Ambiguus nucleus. Long narrow column of cells in the reticular formation at rostral and mid medulla levels. Although nucleus cannot be seen in Atlas images, at any given cross-sectional level, it is located approximately halfway between the spinal nucleus of V and the inf olivary complex. Axons from the ambiguus join cranial nerves IX and X. They innervate the ipsilateral pharyngeal constrictors (for swallowing) and laryngeal muscles (for vocalization). Ambiguus also innervates the soft palate muscles. Unilateral ambiguus (or nerve X) lesion. Results in ipsilateral paralysis of above muscles with dysphagia (difficulties in swallowing), dysarthria (difficulties in vocalizing) and deviation of uvula to nonparalyzed side when patient vocalizes. Bilateral ambiguus (or nerve X) lesions results in bulbar palsy with aspiration pneumo Fig. 6 nia, asphyxia, and eventual death. Note that this is similar (but not identical) to “pseudobulbar palsy”, is bilateral corticobulbar Fig. 7 tract lesions. Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 8 of 13 Dr. Jean Peduzzi Nelson Hypoglossal nucleus (Motor Nucleus of CN XII) (Fig. 1) Hypoglossal nucleus. Column of cells next to the midline at mid and caudal medulla levels. Axons from nucleus course ventrally, just lateral to med lemniscus and then lateral to pyramid, after which they exit medulla at the preolivary sulcus. Unilateral XII nerve (or nucleus) lesion. Results in ipsilateral paralysis of intrinsic and extrinsic tongue muscles. When protruded tongue deviates to paralyzed side. In time fasciculations and atrophy of ½ the tongue occur. Unilateral XII nerve and PT lesion. Basically, at levels of the medullary pyramid, results in the inferior alternating hemiplegia with signs of XII as above + PT syndrome. No facial paralysis accompanies this syndrome. (Fig. 8) Inferior alternating hemiplegia (medial medullary syndrome):CN XII & PT Fig. 8 Spinal Accessory (XI) Motor Nucleus (Figure 1) While the XI nucleus is located at the level of the spinal cord, the UMN fibers innervating it are considered part of the corticobulbar tract. Spinal accessory nucleus. This is another long, narrow column of cells found in the gray horn at the transition between medulla and spinal cord and from C1-5 spinal levels. Axons from the nucleus leave spinal cord halfway between the dorsal and ventral roots, then rootlets coalesce to form the nerve which ascends and enters the skull through the foramen magnum only to leave the skull through the jugular foramen. Axons eventually innervate the ipsilateral sternocleidomastoid and trapezius muscles. Unilateral XI nerve lesion. Causes ipsilateral paralysis of the above muscles with downward and outward rotation of ipsilateral scapula. The patient has difficulties turning the head to the side opposite the lesion (especially when resistance is applied) and shrugging at the shoulder. Please remember that in addition to all the brainstem LMNs covered in this lecture, the alpha and gamma motor neurons at all cross-sectional levels of the spinal cord are considered LMNs!!!!  Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 9 of 13 Dr. Jean Peduzzi Nelson Upper Motor Neurons Corticobulbar Lower Motor Neurons (direct → Synapse on cranial motor neurons muscle) CN V nu. bilateral but > contra CN V nu. or nerve Transient jaw → opposite side of lesion jaw → lesion side, difficulty chewing, hyperacusis CN VII nu. CN VII nu. or nerve dorsal ½ nucleus – bilateral Ipsilateral paralysis entire face (Bell’s palsy) ventral ½ nucleus – contralateral hyperacusis Lower face paralysis opposite side of lesion CN IX and X nu. bilateral innervation CN IX and X nu. or nerve (nu. ambiguus) (nucleus ambiguus) gag reflex Ipsilateral dysphagia, ipsilateral dysarthria uvula → opposite lesion CN XI nu. (bilateral innervation) CN XI nu. or nerve Ipsilateral to lesion scapula down & out Difficult shrugging on side ipsi to lesion Difficult turning head to contralateral to lesion CN XII nu. (bilateral but > contra) CN XII nu. or nerve Transient tongue → opposite side of lesion Tongue → lesion side on protrusion on protrusion Motor Involvement in Brown-Sequard Syndrome (Fig. 9) Destroys LMNs in ventral horn that results in LMN symptoms at site of injury Damages lateral corticospinal tract so UMN symptoms caudal to level of injury No clinical signs due to destruction of anterior corticospinal tract Fig. 9  Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 10 of 13 Dr. Jean Peduzzi Nelson 1. What symptoms would you expect in lesion of one side of the spinal cord? Choose one or more answers. A. Ipsilateral flaccid paralysis at level of the lesion B. Contralateral loss of pain and temperature below the lesion C. Ipsilateral spastic paresis below the lesion D. Ipsilateral loss of vibration and position sense (proprioception) below the lesion E. Ipsilateral loss of all sensory modalities at the level of the lesion 2. Patient has weakness in entire right side of face. Choose 1 or more answers. Where is the lesion? A. Spinal cord B. Right caudal pons C. Right CN VII D. Left caudal pons E. Genu of right internal capsule F. Genu of left internal capsule 3. Patient has weakness in right lower face, right arm & right leg. Where is the lesion? A. Peripheral nerve B. Spinal cord C. Medulla D. Left internal capsule E. Left precentral gyri 4. Patient has weakness in lower right side of face. Choose 1 or more answers. Where is the lesion? A. Caudal to medulla B. Left caudal pons C. Right inferolateral pre-central gyrus D. Genu of right internal capsule E. Left inferolateral pre-central gyrus F. Genu of left internal capsule 5. Patient has weakness in arm & leg on 1 side. Where is the lesion? Choose 1 or more answers. A. Peripheral nerve B. Spinal cord below C5 C. Medulla to C4 D. Pyramidal tract rostral to pons E. Precentral gyri Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 11 of 13 Dr. Jean Peduzzi Nelson 1. What symptoms would you expect in lesion of one side of the spinal cord? Choose one or more answers. A. Ipsilateral flaccid paralysis at level of the lesion (damaged motor neuron in ventral horn) B. Contralateral loss of pain and temperature below the lesion (ALS aka lateral spinothalamic tract) C. Ipsilateral spastic paresis below the lesion (damaged lateral corticospinal tract) D. Ipsilateral loss of vibration and position sense (proprioception) at & below the lesion (DC-ML) E. Ipsilateral loss of all sensory modalities at the level of the lesion (sensory neurons, dorsal root) All of the signs/symptoms choices would be present 2. Patient has weakness in entire right side of face. Choose 1 or more answers. Where is the lesion? A. Spinal cord B. Right caudal pons C. Right CN VII D. Left caudal pons E. Genu of right internal capsule F. Genu of left internal capsule B or C is correct. Facial motor nucleus is located in caudal pons. If corticobulbars were damaged, only lower face weakness is observed. Corticobulbars (UMN) can’t influence damaged LMNs. Lesion of CN VII or CNVII nucleus would have same result. Bell’s palsy can result from infection or blood vessel impinging on nerve. R L Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 12 of 13 Dr. Jean Peduzzi Nelson 3. Patient has weakness in right lower face, right arm & right leg. Where is the lesion? A. Peripheral nerve B. Spinal cord C. Medulla D. Left internal capsule E. Left precentral gyri D is most likely because corticobulbar & corticospinals are in close proximity in internal capsule. E is unlikely because a large lesion of entire precentral gyrus would have sensory deficits. R L 4. Patient has weakness in lower right side of face. Choose 1 or more answers. Where is the lesion? A. Caudal to medulla B. Left caudal pons C. Right inferolateral pre-central gyrus D. Genu of right internal capsule E. Left inferolateral pre-central gyrus F. Genu of left internal capsule E or F is correct. Wouldn’t be caudal pons because can’t get lesion of corticonuclears without damaging CN VII nucleus resulting in entire face deficits. Can’t be right side because corticobulbars are more strongly crossed.  Lower Motor Neurons (LMNs) and Combined LMN/UMN Lesions Page 13 of 13 Dr. Jean Peduzzi Nelson 5. Patient has weakness in arm & leg on 1 side. Where is the lesion? Choose 1 or more answers. A. Peripheral nerve B. Spinal cord below C5 C. Medulla to C4 D. Pyramidal tract rostral to pons E. Precentral gyri C or E is correct. C: Anywhere from medulla to C4 could be possible. If caudal to pyramidal decussation (crossing), ipsilateral side would be affected. Must be above C5 or upper extremity muscles would be affected. E: Although leg is represented medially, it is not distant to area representing arm. Contralateral effects if cortical. D is incorrect because this would also result in lower face paresis due to loss of corticobulbars. Mistake in recording, D is incorrect if there is no lower facial weakness. Question should have been clearer stating whether or not there was any facial weakness or paralysis. R L