Examination and Evaluation of Sensory Systems PDF

# Examination and Evaluation of Sensory Systems ## Sensation * "a feeling; the translation into consciousness of the effects of a stimulus exciting any of the organs of sense" (Stedman, 1982). * The term sensation implies that the feeling or impression is conveyed to and processed by the central n...

# Examination and Evaluation of Sensory Systems ## Sensation * "a feeling; the translation into consciousness of the effects of a stimulus exciting any of the organs of sense" (Stedman, 1982). * The term sensation implies that the feeling or impression is conveyed to and processed by the central nervous system. * However, some important sensory systems will be discussed (e.g., spinocerebellar "unconscious" proprioception) that are processed primarily at a subconscious or unconscious level although, * Most sensation is processed at an awareness level and is therefore termed conscious sensation. * Sensation reflects information from the internal or external environment. * The modalities of sensation are the specific types of sensation including pain, pressure, and joint position sense. ## Introduction * Sensation includes all incoming information brought into the nervous system, whether processed consciously or subconsciously. * **Sensibility:** "the capability of perceiving sensible stimuli" * **Cortical sensibility** processed by the cerebral cortex is the recognition of sensory information & related discrimination of sensory impression. * **Threshold stimulus:** the minimal stimulus level that will produce a sensation. * **Afferent impulses** is used for sensory or incoming signals, while * **Efferent impulses** are those that transmit information away from the NS to an effector organ (muscle or gland). * The examination methods described in detail in this chapter address sensory components from four categories: superficial sense, discriminative sense, proprioceptive sense, and chronic pain. ## Categories of Sensation * Sensory modalities or the types of sensory input can be generally divided into two broad categories: superficial or deep. ### Superficial sensation (tactile sensation): * All sensations detected by receptors at the surface of the body and are usually associated with the skin or skin appendages. * Includes pain, temperature, light touch, and pressure touch. ### Deep sensations generally called(proprioception): * May be processed consciously or subconsciously and * It include sensations related to position or movement of a joint or body segment or awareness of length of a specific muscle. ## Superficial Sensation * **Pain sensibility:** the unpleasant feeling resulting from a sensory stimulus that is sharp or pinpoint, especially when the stimulus has the potential to cause tissue damage. * This sensory modality, protective in nature, can also be referred to as sharp/dull discrimination. * **Temperature sensibility** interprets the heat or cold state of an object or environment and also plays a protective role. * **Light touch** is the sensation caused by the mildest of tactile stimulation even slight contact + separate receptor types in skin with hair and hairless or glabrous skin. * **Pressure touch** sensation results from mechanical stimulation due to a greater magnitude of pressures with deeper skin deformation. ## Discriminative Sensations * Include vibration, tactile localization, two-point discrimination, graphesthesia, stereognosis. * The last four of these are often considered to be perceptual processes requiring integration of numerous sensory signals + multiple sensory modalities + not purely sensory. * **Vibration** is the sensation experienced from tactile contact with an object that is shaking or oscillating at a particular frequency. * **Tactile localization** is awareness of the specific skin surface site to which stimulation was applied and is * **Characterized & documented** by the distance error between the actual site of stimulus and the subject-reported site of stimulus. * **Twopoint discrimination sensibility** is the ability to distinguish two simultaneously applied blunt points as two discrete stimuli. * The smallest interpoint distance still perceived as two points quantifies the threshold of two-point discrimination. * **Graphesthesia** is the recognition of symbols traced on the patient's palm including shapes, numbers, or letters. * **Stereognosis** is the ability to recognize, by tactile manipulation only, the form and characteristics of an object including size, shape, weight, consistency, and texture. ## Deep Sensations * Include joint position sense and joint movement sense * They are very important components of feedback as a basis for motor control. * **Joint position sense**, sometimes simply referred to with the generic term proprioception, is the awareness of static positions of a single joint or body segment detected without use of vision. * **Joint movement sense**, often called kinesthesia, is awareness of the degree, velocity, and direction of movement at a single joint or body segment also internally detected through muscle and joint receptors. ## Sensory Receptors * Each sensory modality has specific sensory receptors (Fig. 5-1) converting the specific form of energy (mechanical, thermal, chemical, or electromagnetic) into an action potential transmitted into the CNS as afferent action potentials or impulses. * The modalities of light touch, pressure touch, pain, vibration, and proprioception use receptors categorized as mechanoreceptors. * Pain impulses can be initiated by a class of receptors called nociceptors or nocioceptors, most commonly free nerve endings, but also from the effect of temperature extremes on heat and cold receptors. * **Temperature sensation is detected by thermal receptors.** Cold and warmth receptors, located under the skin with cold receptors positioned at greater depth than warmth receptors * 3 to 4 times as many cold receptors as warmth receptors in most areas of the body, * greatest density in the lips (15 to 25 cold points per square centimeter) compared with fingers (3 to 5 cold points per square centimeter) and certain broad surface areas like the trunk (less than 1 cold point per square centimeter). ### Superficial Mechanoreceptors: detect mechanical deformation * In the skin includes (especially for temperature, touch, and pressure): * Free nerve endings (touch and temperature) * Hair end organs (light touch) * Ruffini's spray endings (warmth and movement) * Encapsulated Meissner's corpuscles (light touch and vibration) * Encapsulated Krause's corpuscles (cold) * Expanded endings = Merkel's dis (light touch) ### Deep Mechanoreceptors (especially for pressure): * In the deeper tissues include free nerve endings, expanded nerve endings, and * encapsulated Pacinian corpuscle (deep pressure and vibration) ### Muscle spindles (unconscious proprioception) ### Golgi tendon organs (unconscious proprioception) ## Table of Sensory Modality Details | Sensory Modality | Receptors Utilized | Name (and Location of Spinal Pathway) | Level and Name of Decussation | |---|---|---|---| |**Pain (sharp/dull)**| Free nerve endings (FNE), (also in muscle and joint capsule), thermoreceptors|Lateral spinothalamic tract (in contralateral anterolateral spinal cord) |Fibers from posterior horn cells cross within one to two levels of entry into the spinal cord through the "anterior commissure."| |**Temperature**|Free nerve endings| Lateral spinothalamic tract (in contralateral anterolateral spinal cord) |Fibers from posterior horn cells cross within one to two levels of entry into the spinal cord through the "anterior commissure."| |**Touch**|Merkel's disks*, FNE, hair follicle endings, Ruffini endings, Krause's end-bulb, and possibly Meissner's corpuscles | Anterior spinothalamic tract (AST) (in contralateral anterolateral spinal cord) and medial lemniscal (ML) system (in ipsilateral posterior columns of spinal cord)|AST fibers from posterior horn cells cross within one to two levels of entry into the spinal cord through the "anterior commissure;" ML fibers cross from nucleus cuneatus and nucleus gracilis in low medulla as the "internal arcuate fibers."| |**Pressure**|Pacinian corpuscles, FNE (also in muscle), Ruffini endings (especially for maintained pressure), Krause's end-bulb|Medial lemniscal system: fasciculus gracilis and fasciculus cuneatus (in ipsilateral dorsal column of spinal cord); becomes the medial lemniscus (in the low medulla of the brainstem)|Fibers cross from nucleus cuneatus and nucleus gracilis in low medulla as the "internal arcuate fibers."| |**Two-point discrimination**|Merkel's disks*|(Same as pressure)|(Same as pressure)| |**Tactile localization**|Merkel's disks*, Meissner's corpuscles|(Same as pressure)|(Same as pressure)| |**Discriminative touch (stereognosis, texture)**|Meissner's corpuscles*|(Same as pressure)|(Same as pressure)| |**Vibration**|Pacinian corpuscles*|(Same as pressure)|(Same as pressure)| *Pacinian corpuscles are located subcutaneous and within deep tissues (muscle, tendon, and joint soft tissue) |**Joint Position and Movement sense (conscious)**|Muscle spindles, joint receptors, golgi-type endings in ligaments, Ruffini endings in joint capsule and ligaments (for direction and velocity), free nerve ending in joint capsule (for crude awareness), Paciniform endings in joint capsule (especially for rapid joint movements)|(Same as pressure)|(Same as pressure)| |*Pacinian and Meissner corpuscles are quickly adapting receptors for moving touch. Merkel's disks, in hairy and glabrous skin, are slowly adapting to detect constant touch, low intensity, and velocity of touch.* |**Tension of muscle**|Golgi tendon organ (protective function for muscle)|(Same as pressure)|(Same as pressure)| ## Functional Implications * The sensory systems & the information they provide CNS are essential for optimal control and efficiency of movement. * **Tactile sensation** provides important clues regarding the interaction of each body part with the environment, including supporting structures, perturbing objects, and external forces. * For example, **pressure sensation from the sole of the foot** provides feedback related to COG location essential for optimal balance control in standing. * When leaning forward, more weight is sensed through the forefoot plantar surface. Leaning backward causes increased pressure through the heel of the foot and less through the forefoot. * **Joint position sense & movement sense** provide feedback about muscle length & joint angles as movement occurs. * This proprioceptive feedback is essential for optimal motor control and the fine adjustments needed for skilled coordinated movement during tasks and activities ## Functional Implications Continued * In neuromuscular disease or trauma, * damage may occur to the **peripheral receptors**, * **afferent pathways** (peripheral nerve, spinal cord, brainstem, or cortical white matter), * **central relay nuclei** (brainstem nuclei, thalamus, basal ganglia), * **areas of sensory cortex** (primary, secondary, or association). * increases the **risk of injury** to self and requires increased visual attention to affected areas for minimizing injury risk. Impaired joint position sense could **diminish ongoing motor adjustments** resulting in **poorly controlled movement**. * the person may experience **partial or complete loss of sensation**. ## Where is It? **Lateral view of brain and spinal cord** **Post-central gyrus** **Ventral-posterior nuclei of thalamus (VPM & VPL)** **Horizontal section of brain** **Medial lemniscus: Fasciculus cuneatus Anterolateral system (lateral spinothalamic tract)** **Posterior Fasciculus gracilis Dorsal horn and base of dorsal root** **Horizontal section of spinal cord** **Figure 5-2** Major sensory locations of the central nervous system (within brain, brainstem, and spinal cord). These drawings highlight neuroanatomic sites related to sensation. In the brain, the postcentral gyrus is the primary somatosensory cortex, and ventral posteromedial (VPM) and ventral posterolateral (VPL) of the thalamus are processing and relaying nuclei for sensory information from the face and body, respectively, traveling to the cortex. In the spinal cord, the posterior funiculus carries the discriminative general senses of the medial lemniscal system, the posterior horn of the spinal cord houses most sensory nuclei, and the anterolateral system of the spinal cord carries light-touch and pain/temperature sensations. **Postcentral gyrus** **Arm Hand Face Trunk Leg** **Lateral ventricle Caudate Thalamus Put LGP MGP Midbrain Pons Medulla Spinal cord** **Cervical enlargement** **Lumbosacral enlargement** **Spinal cord section** **Figure 5-3** Longitudinal drawing of major sensory pathways. This figure illustrates the central nervous system sensory pathways for medial lemniscus/posterior columns (carrying discriminative general senses) in blue and both lateral spinothalamic (carrying pain and temperature) and anterior spinothalamic (carrying light touch) in red. The location shown for terminus of medial lemniscus fibers on the inferior right postcentral portion of the paracentral lobule approximately represents sensation carried from the distal left lower extremity. The location shown for terminus of lateral spinothalamic fibers on the lateral surface (midportion) of the right postcentral gyrus approximately represents sensation carried from the proximal left upper extremity. ## General Principles for Sensory * **I-** primarily investigates the status of the **consciously processed** sensory modalities. * For most aspects of sensory examination, you will ask the patient to **respond based** on his or her awareness of the sensory input given. * **II-** For **unconscious sensations systems**, we can only make **indirect inferences** or deductions based on what we observe to be contributions make to movement. * Example is the **_processing unconscious proprio-ception at the level of the cerebellum_.** ## General Principles for Sensory Continued * **Start with screening questions** such as, "Are there any areas of your skin where your feeling has changed or decreased?" * In **cerebrovascular pathology**, with expected asymmetry, you might ask the question, "Does the skin of one side of your body feel different to you than the other side? What parts?" * **Quickly draw your attention to problem areas**, although the whole body needs to be tested. * For each modality tested, **visually demonstrate the method to the patient before you start the actual testing** so the patient knows what to expect. * Apply the stimulus **first to an area where you don't expect to find impairment** (for example, the "unaffected side" in a person with CVA or UL in a person with paraplegia) allowing the patient to watch. * At this point, as the patient watches, **you should also clearly define response terms and response options with the patient:** "This is sharp," "This is dull," or "We'll call this right and this left." * After demonstrating the method, **vision should be eliminated during each sensory test.** * As with other aspects of examination, the patient may want to "perform well" and may, without intention, be driven to give the "right" response whether it is felt or not. * In some cases, this may be a **reflection of cognitive and perceptual status**, including impulsivity. * **Elimination of vision will assure patient responses** are strictly based on the sensation being tested without visual compensation. * Each stimulus or test position should be maintained for several seconds and not just applied instantaneously. * **allowing sufficient time for central processing and response.** * **Do not move too quickly from one test site to the next**, especially if it is an adjacent area. * This may interfere with **central processing and verbal response** and may have a summation effect as a previous stimulus may reinforce the current stimulus. * **If the patient is unable to respond verbally**, you will need to develop an alternative method for patient response such as, "Blink your eyes if 'dull,' or open your eyes wide if 'sharp." * If **cognitive deficits prevent accurate responses** (also in pediatric patients), the therapist may have to infer sensibility based on the patient's nonverbal and motor response to introduced stimuli. * All parts of the sensory examination (superficial, deep, and discriminative senses) **should be performed bilaterally for comparison** of specific locations on right and left sides. * The **sequence of specific locations tested** is different depending on whether you are doing superficial or deep sensation testing. ## Sequence of Sensory Testing * Testing modalities of superficial sensation is best organized around dermatomes. * It is important to remember the top half of one dermatome overlaps with the lower half of the dermatome above it, and the bottom half of a dermatome overlaps with the top half of the dermatome below it, as shown in Figure 5-4. * Also remember that C5-T1 roots supply the brachial plexus to serve the upper extremity, and L2-S3 roots contribute to the lumbosacral plexus for the lower extremity. Therefore, T2-L1 roots are dedicated to trunk dermatomes alone. * Some of the key surface landmarks associated with dermatome levels are summarized in Table 5-2 * The skin of the face & cheek mucosa is actually supplied by the Trigeminal nerve, and full assessment of this cranial nerve * testing modalities of superficial sensation is best organized around dermatomes. * For sensory evaluation of the body, it will **enhance consistency** if you always test the dermatomes in a systematic order. * **For example, you could test top to bottom,** * for example, top and back of head for C1-2; * back of neck and upper trunk for C3-4; * circumferentially around each arm and forearm and across the fingertips of first, third, and fifth digits for C5-T1; * paramedian along the anterior trunk for T2-L1 and * circumferentially around lower extremity beginning with anterior iliac crest and including the superior surface of the foot for L2-S3. * Testing anteriorly on the trunk will reveal peripheral nerve lesions there that you may miss if you test on the posterior trunk only. **Figure 5-4** **Figure 5-5** ## Table 5-2 Key Surface Landmarks for Sensory Testing | Dermatome | Skin Over This Surface Structure | |---|---| | C2 | Posterior half of skull| | C3 | Medial end of clavicle| |C4|Medial acromion and below clavicle | |C5|Lateral elbow (and lateral acromion)| |C6|1st digit (and 2nd digit)| |C7|3rd digit| |C8|5th digit (and 4th digit)| |TI|Medial elbow| |T2|Anterior axilla| |T4|Nipple line | |T6 or T7|Xiphoid process| |TIO|Umbilicus| |T12|Anterior iliac crest/pubic symphysis | |LI|Inguinal region (upper medial thigh)| |L2|Medial thigh-mid-distance| |L3|Medial knee| |L4|Medial malleolus| |L5|Base of great toe (and lateral aspect leg/plantar aspect to heel)| |SI|Lateral heel (base of 5th digit, fibula head, lateral malleolus, little toe) | |S2|Posterior knee| |S3|Ischial tuberosity| ## Sequence of Sensory Testing (discriminative and deep sensations) * The testing sequence for discriminative and deep sensations is not organized around dermatomes but **joints & body regions**. * Because these tests are performed more globally than superficial sensation tests, a chart organized by body region is ideal for documentation of these sensations. * The testing sequence for discriminative and deep sensation testing as part of a comprehensive sensory evaluation therefore includes: * Areas of the face (forehead, cheek, lips) and, * For proprioception, joint regions including jaw, neck, shoulder, elbow, wrist, interphalangeal (IP) joints, spine, hip, knee, ankle, and toes. ## Parameters of Sensory Impairment to Investigate * Based on the medical diagnosis of the patient + an understanding of the related pathophysiology, the therapist will have some idea of possible sensory deficits and their expected body distribution even before starting the examination. * When a sensory impairment is identified in a particular patient, the next step is to determine the parameters or characteristics of the identified sensory impairment including * Quantity of the sensory impairment * Quality of the sensory impairment. ## Quantity of Sensory Impairment * Includes all characteristics related to the extent, size, and regional dimensions of the deficit (five possible distribution patterns): . * Sensory deficits associated with cerebral or brainstem pathology (central nervous system) usually occur in a **unilateral distribution** * (often involving both the arm and leg on the side of the body contralateral to the central nervous system pathology). * Either a **paraplegic distribution** (Fig. 5-5B) (involvement of lower extremities and trunk, but arm function is unimpaired). a **tetraplegic (quadriplegic) distribution** (lower extremities and upper extremities) of sensory loss is associated with spinal cord injury with sensory loss only in tissues innervated from below the injury level. * **Dermatomal distribution** of sensory symptoms is related to nerve root lesions resulting in band-like areas of sensory loss as shown earlier in the dermatomal maps (Fig. 5-4). A peripheral nerve lesion will result in a peripheral nerve distribution of sensory loss characteristic of the **particular cutaneous nerve distribution for the lesioned nerve** (Fig. 5-5C). * A general peripheral distribution of sensory deficits, also described as **"stocking/glove distribution,"** occurs generally in the distalmost parts of the limbs (feet and hands). Figure 5-5D * Most commonly with peripheral neuropathy, especially chronic diabetes and other metabolic conditions. For comparison, an L5 dermatomal distribution of sensory loss is shown in Figure 5-5E. * A distribution of sensory deficits sometimes occurs that follows no pattern and is termed a **sporadic distribution**. A sporadic distribution is usually **asymmetrical**, perhaps affecting both sides but different regions on each side (see Fig. 5-5F). ## Figure 5-5 ## Table 5-3 Clinical Significance of a Variety of Semmes-Weinstein Monofilaments | Semmes-Weinstein Filament | Force Applied With Filament | Clinical Significance | |---|---|---| | 1.65 | 4.5 mg | The smallest filament in the complete set <br/> Useful predictor of normal in females because of a lower threshold for pressure sensitivity (Bell-Krotoski, 1993) | | 2.44 | | | | 2.83 | | Considered "within normal limits" <br/> Useful to screen for sensory abnormality anywhere in the upper extremity (Bell-Krotoski, 1993;Van Deusen, 1997) <br/> Suprathreshold for the face, subthreshold for foot callous areas (Bell-Krotoski, 1993) | | 3.22 | 166 mg | Threshold mapping at this level indicates an area with less than normal sensitivity (Bell-Krotoski, 1993) | | 3.61 | 200 mg | Pressure threshold at this level is associated with some loss of graphesthesia and texture recognition (Bell-Krotoski, 1993) | | 3.84 | 500 mg | Pressure threshold at this level is associated with diminished protective sensation, impaired stereognosis, and usually loss of two-point discrimination (Bell-Krotoski, 1993) | | 4.17|1 gram|Normal sensation| | 4.31 | 4 grams | Pressure threshold at this level is associated with absent stereognosis + protective sensation (Bell-Krotoski, 1993) | | ≥4.56 | >4 grams | These larger filaments simply measure degrees of deep-pressure sensation (Bell-Krotoski, 1993) <br/> One author reported, from clinical experience only, that patients who responded only to these larger filaments may have response to pinprick, but not enough protective sensation to respond to stimuli such as a hot cup fast enough to prevent injury (Bell-Krotoski, 1993) | | 5.07 | 10 grams | Useful to screen for sensory abnormality in the feet (Mueller, 1996; Sloan, 1998) <br/> Pressure threshold at this level is the best indicator of protective sensation in the feet (Birke, 1985). Another study concluded that 4.21 was the threshold to differentiate risk of foot ulcers (Sosenko, 1990). | | 6.10 | 75 grams | Useful as a predictor of foot ulceration in patients with noninsulin-dependent diabetes mellitus (compared with a neurometer, which was optimal at 2,000 Hz with high sensitivity (92.9%) and low false-positive rate (26.2%). (Olmos, 1995) | | 6.65 | 447grams | Marked sensory loss if unable to feel this monofilament <br/> The largest filament in the complete set | ## Quality of Sensory Impairment * Includes characterization of the degree of sensory dysfunction. * If sensation is unimpaired or meets some established norms for sensory function, terms like normal or intact are used in the documentation. * If sensation is completely lost and the individual has no sensibility in the affected region, the term absent is used. * If all sensory modalities are lost, the term anesthesia is used. * In between these two extremes are the cases where there is some degree of sensation detected in the affected region, but subjectively the patient reports a decrease in intensity compared with what is typically felt for that region or the person is less consistent in the report or performance used to demonstrate the sensory ability. In this case, the sensation is categorized as impaired. * Several terms are used to describe abnormalities of sensory integrity (impaired): * **Hypoesthesia or hypesthesia** is a decrease in sensibility or awareness. * **Hyperesthesia or hypersensitivity** is an excessive or increased sensitivity to sensory stimuli. * **Dysesthesia**, literally "difficult sensation," occurs when an ordinary stimulus results in a disagreeable sensation, and * **Allodynia** is an exaggerated or painful response to a stimulus that should not be painful. * **Paresthesia** is an abnormal negatively perceived sensation that may include burning, pricking, tickling, tingling, or numbness without apparent cause, even in the absence of a known stimulus. ## Keep in Mind * impaired sensation from injury to a single nerve root will not result in absence of sensation in the affected dermatome, but rather hypoesthesia because of the overlap with dermatomes above and below. ## Specific Sensory Examinations * The sensory evaluation is usually performed in a logical order, including * Tests of superficial or tactile sensibility, * Discriminative sensibility, and * Proprioceptive sensibility. ### Superficial (Tactile) Sensation * Includes modalities of: * Sharp/dull (pain), * Temperature, * Light touch, and * Pressure touch. ### Testing Sharp/Dull Discrimination * Sharp/dull testing is used to assess integrity of the "pain" pathway (lateral spinothalamic tract). * **Equipment:** There are several instruments with both a sharp and a dull end that can be used (see Fig. 5-6): * An opened safety pin with partially sanded point (using rounded cap for dull). * A partially opened paperclip (using the curved end for dull). * The pin in the handle of a commercially available neurological reflex hammer. * **Method:** * In each instrument, there is a pointed end for sharp input to the skin and a flat or rounded end for dull input. * Care must be taken when using safety pins, gently sanding the points, as to not pierce the skin. * For infection control of bloodborne pathogens, the safety pin or paperclip should be discarded after each patient and use of reflex hammer pins is discouraged. * **Figure 5-6** * Regardless of the instrument used, deliver the inputs of sharp and dull in a variable order following a systematic dermatomal sequence as previously described. * After demonstrating the sensations to be felt for the patient, the specific method and guidelines for sharp/dull testing are: * Apply the pinpoint with enough force to indent the skin but with very slight or no blanching seen in the adjacent skin. * Hold the pinpoint in place, maintaining the stimulus for several seconds to allow time for central processing and response. * For each input, ask the patient to respond to the question, "Does it feel sharp or dull?" * Each time a stimulus is felt, the patient should respond "sharp," "dull,” or “can't tell.” ### Testing Temperature Sensation * Temperature sensation, carried by the same afferent pathway as pain sensation (lateral spinothalamic tract), is typically evaluated using test tubes of cold and hot water (Cooke, 1991; Harlowe, 1985). * If your evaluation purpose is to test the integrity of the lateral spinothalamic system, there is no need to test both pain sensation and temperature sensation, and most therapists would test for sharp/dull sensation. * Temperature sensation is not frequently tested as part of the neurological evaluation. * **Equipment:** There is sophisticated equipment that has been described for use in testing temperature sense (Horch, 1992; Waylett-Rendall, 1988). In the typical clinical setting, the test is accomplished with much simpler and less expensive equipment: * Two test tubes with stoppers: * One filled with hot water, 104°F to 113°F (40°C to 45°). * One filled with crushed ice and water, 41°F to 50°F (5°C to 10°C). * Exceeding these temperature limits may cause a pain response that would interfere with the validity of the testing (Schmitz, 1994). * **Method:** * If temperature sensation is tested as part of the neurological examination to determine distribution and severity of sensory impairment, the dermatomal sequence and general procedure for tactile sensations should be followed but with hot and cold stimuli as described: * First, test the temperature of the water-filled tubes on your own skin to assure safety. * Then apply hot and cold randomly following the dermatomal sequence, maintaining each contact for several seconds. * The patient is asked to verbally respond for each contact they detect with either "hot," "cold," or "can't tell." ### Testing Light-Touch Sensation * Little research has been published regarding the technique of light-touch evaluation except the Semmes-Weinstein monofilament (SWM) test * **Equipment:** Several options exist clinically for light touch: * A wisp pulled from a cotton ball is most often used. * A thin piece of facial tissue or Kleenex. * A camel hair brush. * **Method:** * Following the general procedure and sequence for superficial sensation: * Apply the selected light-touch sensory input to the skin by very lightly and slowly stroking the surface at one small location. * Ask the patient to respond each time they feel the sensation with an affirmative response such as "O.K." or "now." * To introduce variability in testing, either alter the time interval between applications to prevent patient prediction of the next application or by asking the patient, "Do you feel anything?" at times when you are not applying a light-touch stimulation. * In skin with hair, even the fine hairs on the back of the hand and fingers, the stimulus does not have to be applied directly to the skin surface itself but lightly across the hairs only. * The light-touch receptors wrapped around the base of each hair follicle are exquisitely sensitive. * In glabrous or hairless skin like the palm and sole, the wisp is lightly applied to the surface of the skin. ### Testing Pressure Touch Sensation * Often assessed grossly using pressure through a pencil eraser or pushing deeply with a finger and asking the patient to distinguish between touch of deep and light pressures by responding to each touch with either "deep" or "light." * Pressure touch has been evaluated more objectively using a system of graded weights (Sieg, 1986) but has not gained widespread clinical use. * Weights of 0.5, 1, and 2 ounces were placed in a metal capsule with the blunt end placed on the skin surface to be tested. * You would ask the patient to distinguish between the different weights. * A more objective method for evaluating both light touch and deep pressure uses the SWM aesthesiometer, which has been widely researched (Birke, 1985; Waylett-Rendall, 1988; Weinstein, 1993; Mueller, 1996; Sloan, 1998). * It is most commonly used in populations where more specific measures of sensibility need to be monitored for change, particularly hand injuries including nerve damage, reattachments, or in peripheral neuropathies such as diabetic neuropathy. * **Figure 5-7** * Each aesthesiometer consists of a nylon monofilament (like fishing line) embedded near the end of a plastic rod and emerging at a right angle. * Standardization of each filament by generating a reproducible buckling stress allows quantification of applied forces (Mueller, 1996). * The color-coded number engraved on the rod, ranging from 1.65 to 6.65 (see Table 5-3), represents the logarithm to the base 10 of the force in milligrams required to bow the filament (Waylett-Rendall, 1988). * The higher the assigned number, the more force is required for the filament to bend. * **Equipment:** Depending on the purpose of evaluation, there are several SWM sets commercially available: * A full set consists of 20 filaments (ranging from 1.65 to 6.65), each with a different strength related to length and thickness of the monofilament. * The smaller kit with five varied filaments has been reported as time-efficient and adequate for most clinical settings (Bell-Krotoski, 1993). * The single 2.83 filament can be used alone for upper extremity screening (Bell-Krotoski, 1993; Van Deusen, 1997). This 2.83 filament has also been supported as “suitable for testing most of the body” (Bell-Krotoski, 1993). * A single 5.07 filament, calibrated to bend at 10 grams of force, has been suggested as the best indicator of protective sensation in the feet. (Birke showed that no patient with neuropathic ulcer was able to sense the 5.07 monofilament) (Birke, 1985; Sloan, 1998; Boyko, 1999). * Callous formation on the plantar surface of the foot may cause increased pressure thresholds (Bell-Krotoski 1997). * **Method:** * Have the patient seated or lying and follow the general procedures previously described (including blocking vision). * One possible exception to the testing sequence is that testing may be applied from distal to proximal if the expected impairment is likely in a peripheral distribution. The method can be divided into the following steps: * Apply the filament at 90° to the skin surface with enough force to make the filament bend slightly or buckle (see Fig. 5-7) and maintain for approximately 1 second (Birke, 1985) to 1.5 seconds (Bell-Krotoski, 1997) but not at predictable intervals. A slight adaptation of the application technique shown in Table 5-4 has been suggested depending on the grade of the filament used (Waylett-Rendall, 1988). * Instruct the patient to say "yes" each time sensation of the application of the filament is perceived ("yes-no" method). * At least five trials are recommended at each site before progressing to the next location (Mueller, 1996). * Response must be correct for 80% of the trials (4/5 trials) at a site to be graded with that SWM value at that site (Mueller, 1996). A ratio of two correct responses out of three has also been suggested to be considered intact in that area (Waylett-Rendall, 1988). * If a patient senses less than 80% of trials at a site, proceed to test that area with the next stronger monofilament (the next higher number). * Compare results to normative data (see Box 5-1), especially if cerebral damage has taken place even if unilateral because of a likelihood that both hands are affected (Dannenbaum, 1993). ## Box 5-1 Expected Pressure Sensibility Ranges by Body Regions * Hand localizes pressure between probes 2.44 to 2.83 (Waylett-Rendall, 1988) * Proximal upper extremity localizes between 4.08 to 4.17 (Waylett-Rendall, 1988) ## Table 5-4 ## Discriminative Senses * They are the group of sensations carried by the lemniscal system. * These sensations require cortical processing and integrating information from more than one type of tactile sensory modality to perceive qualities of the object being explored by touch. * Discriminative sensibility has been defined as the capacity for precise interpretation of sensation (Omer, 1983).