The sensory modalities

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From the clinical viewpoint, the important sensory modalities are joint position sense tproprioception), light touch, pin prick, vibration, temperature and two-point discrimination. Other sensory functions are important but will be covered under the section on the cortical examination (see Table 6.24). It is unusual for a patient to experience only one sensory symptom. The aims of sensory testing are:

■ to determine if any modalities are impaired • to determine the site of any lesion from the topographic pattern of dysfunction (e.g. dermatomal distribution, peripheral nerve distribution).

When performing these tests it is important to avoid inflicting unnecessary discomfort upon the patient and to explain what is being performed. If physical signs arc present, the examination should also cover a search for the underlying cause (see Fig, 6.47),

TABLE 6,24 Tests of sensation

Modality

Proprioception

Vibration

Two-point discrimination

Large fast-conducting axons Dorsal columns Medial lemniscus

Pinprick (superficial pain) i Deep pain Temperature

Smaller slower-conducting axons Spinothalamic tracts

Stereognosis Graphaesthesia Two-point discrimination

Parietal cortex (only valid if peripheral sensory function intact)

Sural Nerve Innervation

Supraclavicular nerve Circumflex nerve Lateral cutaneous nerve of arm Medial cutaneous nerve of arm

Musculo-culaneous nerve Sural nerve Anterior tibial nerve

Saphenous nerve

Medial cutaneous nerve of forearm

Lateral cutaneous nerve of forearm

Radial nerve Ulnar nerve Median nerve

Fig. 6.45 Segmental and peripheral nerve innervation and points for testing anterior cutaneous sensation of limbs. By applying stimuli at the points marked, both the dermatomal and main peripheral nerve distribution are tested simultaneously.

Supraclavicular nerve Circumflex nerve Lateral cutaneous nerve of arm Medial cutaneous nerve of arm

Musculo-culaneous nerve Sural nerve Anterior tibial nerve

Saphenous nerve

Medial cutaneous nerve of forearm

Lateral cutaneous nerve of forearm

Radial nerve Ulnar nerve Median nerve

12th thoracic nerve

Lateral cutaneous nerve of thigh

Femoral branch of genitofemoral nerve llio-lnguinal nerve

Medial and intermediate cutaneous nerve of thigh

Obturator nerve

Lateral cutaneous nerve of calf

Fig. 6.45 Segmental and peripheral nerve innervation and points for testing anterior cutaneous sensation of limbs. By applying stimuli at the points marked, both the dermatomal and main peripheral nerve distribution are tested simultaneously.

Examination sequence

Touch

□ Ask the patient to close the eyes and to respond verbally to each touch.

□ Touch the skin with a small piece of cotton wool; tissue paper and light digital touch are alternative stimuli.

□ Avoid regularly timed-stimuli so that the patient does not anticipate the test.

□ Examine the spinal segments sequentially (e.g. in the upper limb start on the outer border of the arm (C5). then proceed downwards to the lateral border of the forearm and thumb (Cb). index finger (C7). etc.).

□ Compare sensation on each limb for symmetry.

□ Outline the borders of any abnormal area of sensation by testing from the hypoaesthetic area towards normal.

□ If the patient complains of dysaesthesia (an uncomfortable or abnormal feeling) map from the normal to the abnormal area.

Pain

□ Because of the risk of transmitted hepatitis and HIV, use a new dressmaking pin or a dedicated disposable pin. Avoid using a hypodermic needle, which is too sharp.

□ Establish a baseline for sharpness (c.g, sternal area) before examining the limb.

Peripheral Nerve Leprosy

Supraclavicular nerve

Tibial and lateral plantar nerves Medial plantar nerve

Saphenous nerve

Fig. 6.46 Segmental and peripheral nerve innervation and points for testing posterior cutaneous sensation of limbs. By applying stimuli at the points marked, both the dermatomal and main peripheral nerve distribution are tested simuitaneously.

Supraclavicular nerve

Tibial and lateral plantar nerves Medial plantar nerve

Circumflex nerve Lateral cutaneous nerve of arm Posterior cutaneous nerve of arm Medial cutaneous nerve of arm Medial cutaneous nerve of forearm

Posterior cutaneous nerve of forearm Lalera! cutaneous nerve of forearm

Radial nerve Ulnar nerve

Median nerve Lumbar nerves Sacral nerves Obturator nerve

Posterior cutaneous nerve of thigh Lateral cutaneous nerve of thigh Lateral cutaneous nerve of calf Sural nerve

Saphenous nerve

Fig. 6.46 Segmental and peripheral nerve innervation and points for testing posterior cutaneous sensation of limbs. By applying stimuli at the points marked, both the dermatomal and main peripheral nerve distribution are tested simuitaneously.

□ Test pin prick sensation down cach limb and over the trunk.

□ Ask the patient to report if the quality of sensation changes, either becoming blunter fhypoaesthesia) or feeling sharper or more painful (hyperesthesia).

□ Test each dermatome in turn, but also bear in mind peripheral nerve distributions.

□ Map out the boundaries of any abnormal area as described for light touch.

Deep pain

□ Squeeze muscle bellies (e.g. calf, biceps or triceps) or apply firm compression over the patient's fingernail and toenail beds.

□ Ask the patient to report as soon as the sensation becomes painful.

Temperature

□ Touch the patient with a cold object (e.g. a tuning fork) and ask the patient about the quality of the temperature sensation. This can be performed on face, forearms, hands, trunk and legs.

□ For improved discrimination fill two plastic containers (e.g. serum bottles) one with warm and the other with

Ask about: Diabetes Alcohol

Drug consumption, e.g. amiodarone, vincristine

Renal symptoms Travel Weight loss

Diet, e.g. folate deficiency

Sensory Testing Big Toe

Fig. 6.49 Testing for position sense in the big toe.

Fig, 6.47 General assessment of a perl pheral neuropathy.

cool water. Ask the patient to ciose the eyes and to distinguish between warm and cool while applying the containers to the skin in a random sequence.

Joint position sense (JPS)

□ Test this sensation initially ai the most distal part of the limb, in the upper limb, first test at the distal interphalangeal joint of the index finger.

□ Show the patient the intended movements of the joint and name them (e.g. 'that's up' and "that's down").

□ Ask the patient to close the eyes and to avoid guessing.

□ Grasp the proximal phalanx of a linger with one hand while holding the medial and lateral borders of the distal phalanx of the same finger with the other1 thumb and finger.

□ Move the patient's distal phalanx up and down.

□ Ask the patient to identify the direction of movement during a random sequence of small movements (e.g. up, down, down, up).

□ Then test the contralateral limb.

□ If there is any abnormality of JPS at the distal

Fig. 6.49 Testing for position sense in the big toe.

interphalangeal joint, test at the proximal interphalangeal joint and, if necessary, at the metacarpophalangeal joint, progressing to the wrist and elbow if JPS remains impaired.

□ In the lower limb start at the interphalangeal joint of the big toe. holding the proximal phalanx in the other hand (Fig. 6.48).

□ Take care to ensure thai the examiner's fingers do not rub against the patient's other toes.

□ If there is impairment proceed to examine the metatarsophalangeal joint and, if necessary, the ankle and knee.

Vibration sense

□ Examine the patient with his or her eyes closed.

□ First hold the vibrating tuning fork (128 Hz) over the sternum so that the patient identifies the sensation.

□ in the lower limbs lest the big toe (Fig. 6.49A), If necessary, next move proximally in turn to the ankle (Fig. 6.49B), tibial shaft and tuberosity and the anterior iliac crest.

□ In the upper limbs test the interphalangeal joint of the forefinger: if impaired, proceed to the metacarpophalangeal joint and then more proximal bony prominences.

□ If in doubt, ask the patient to identify as soon as the tuning fork stops vibrating when 'stopped' by the examining lingers.

Two-point discrimination

□ Use a two-point discriminator if one is available, or an opened-out paper clip.

□ Perform the test with the patient's eyes closed.

Distal muscle wasting

Two Point Discrimination

Ulcers

Finger clubbing

Burns/ulcers Vascular bruits

Diabetic retinopathy Butterfly rash Smooth tongue Goitre

Carcinoma of the bronchus

Liver and spleen

Nerve thickening (leprosy)

Small kidneys

Bone marrow (dysfunction)

Ulcers

Finger clubbing

Distal muscle wasting

Burns/ulcers Vascular bruits m

Fig. 6.49 Testing vibration sensation at [3 the big toe and [H the ankle.

Fig. 6.49 Testing vibration sensation at [3 the big toe and [H the ankle.

□ Hold the patient's index finger and apply either one or two of the test object points to the linger pulp.

□ Ask the patient lo determine if one or two stimuli were applied.

□ Then determi ne the minimum distance at which two points are fell lo be separate.

□ Perform the test 011 the pulp of both index fingers and thumbs.

□ Repeat the test several times during the course of the clinical examination lo determine variation in two-point discriminatory distance.

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  • Rudigar
    What are the 6 sensory modalities?
    6 years ago

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