Small Joint Position Sense Test And B12 Deficiency

Here all sensation in the hand is lost. Repetitive testing in a proximal direction reveals a gradual change to normal sensation at the wrist. This pattern fits neither a peripheral nerve nor a dermatome (see pp. 542-546). If bilateral, it suggests the "glove and stocking" sensory loss of a polyneuropathy, often seen in alcoholism and diabetes.

Analgesia refers to absence of pain sensation, hypalgesia to decreased sensitivity to pain, and hyperalgesia to increased sensitivity.

Anesthesia is absence of touch sensation, hypesthesia is decreased sensitivity, and hyperesthesia is increased sensitivity.

Vibration sense is often the first sensation to be lost in a peripheral neuropathy. Common causes include diabetes and alcoholism. Vibration sense is also lost in posterior column disease, as in tertiary syphilis or vitamin B12 deficiency.

Testing vibration sense in the trunk may be useful in estimating the level of a cord lesion.

By identifying the distribution of sensory abnormalities and the kinds of sensations affected, you can infer where the causative lesion might be. Any motor deficit or reflex abnormality also helps in this localizing process.

Before each test below, show the patient what you plan to do and what responses you want. Unless otherwise specified, the patient's eyes should be closed during actual testing.

Pain. Use a sharp safety pin or other suitable tool. Occasionally, substitute the blunt end for the point. Ask the patient, "Is this sharp or dull?" or, when making comparisons, "Does this feel the same as this?" Apply the lightest pressure needed for the stimulus to feel sharp, and try not to draw blood.

To prevent transmitting a blood-borne infection, discard the pin or other device safely. Do not reuse it on another person.

Temperature. (This is often omitted if pain sensation is normal, but include it if there is any question.) Use two test tubes, filled with hot and cold water, or a tuning fork heated or cooled by water. Touch the skin and ask the patient to identify "hot" or "cold."

Light Touch. With a fine wisp of cotton, touch the skin lightly, avoiding pressure. Ask the patient to respond whenever a touch is felt, and to compare one area with another. Calloused skin is normally relatively insensitive and should be avoided.

vibration sense is impaired, proceed to more proximal bony prominences (e.g., wrist, elbow, medial malleolus, patella, anterior superior iliac spine, spinous processes, and clavicles).

Position. Grasp the patient's big toe, holding it by its sides between your thumb and index finger, and then pull it away from the other toes so as to avoid friction. (These precautions prevent extraneous tactile stimuli from revealing position changes that might not otherwise be detected.) Demonstrate "up" and "down" as you move the patient's toe clearly upward and downward. Then, with the patient's eyes closed, ask for a response of "up" or "down" when moving the toe in a small arc.

Repeat several times on each side, avoiding simple alternation of the stimuli. If position sense is impaired, move proximally to test it at the ankle joint. In a similar fashion, test position in the fingers, moving proximally if indicated to the metacarpophalangeal joints, wrist, and elbow.

Discriminative Sensations. Several additional techniques test the ability of the sensory cortex to correlate, analyze, and interpret sensations. Because discriminative sensations are dependent on touch and position sense, they are useful only when these sensations are either intact or only slightly impaired.

Screen a patient with stereognosis, and proceed to other methods if indicated. The patient's eyes should be closed during all these tests.

■ Stereognosis. Stereognosis refers to the ability to identify an object by feeling it. Place in the patient's hand a familiar object such as a coin, paper clip, key, pencil, or cotton ball, and ask the patient to tell you what it is. Normally a patient will manipulate it skillfully and identify it correctly. Asking the patient to distinguish "heads" from "tails" on a coin is a sensitive test of stereognosis.

■ Number identification (graphes-thesia). When motor impairment, arthritis, or other conditions pre-

Loss of position sense, like loss of vibration sense, suggests either posterior column disease or a lesion of the peripheral nerve or root.

The inability to recognize numbers, like astereognosis, suggests a lesion in the sensory cortex.

When touch and position sense are normal or only slightly impaired, a disproportionate decrease in or loss of discriminative sensations suggests disease of the sensory cortex. Stereognosis, number identification, and two-point discrimination are also impaired by posterior column disease.

Astereognosis refers to the inability to recognize objects placed in the hand.

The inability to recognize numbers, like astereognosis, suggests a lesion in the sensory cortex.

vent the patient from manipulating an object well enough to identify it, test the ability to identify numbers. With the blunt end of a pen or pencil, draw a large number in the patient's palm. A normal person can identify most such numbers.

Lesions of the sensory cortex increase the distance between two recognizable points.

Lesions of the sensory cortex impair the ability to localize points accurately.

With lesions of the sensory cortex, only one stimulus may be recognized. The stimulus on the side opposite the damaged cortex is extinguished.

■ Two-point discrimination. Using the two ends of an opened paper clip, or the sides of two pins, touch a finger pad in two places simultaneously. Alternate the double stimulus irregularly with a one-point touch. Be careful not to cause pain.

Find the minimal distance at which the patient can discriminate one from two points (normally less than 5 mm on the finger pads). This test may be used on other parts of the body, but normal distances vary widely from one body region to another.

■ Point localization. Briefly touch a point on the patient's skin. Then ask the patient to open both eyes and point to the place touched. Normally a person can do so accurately. This test, together with the test for extinction, is especially useful on the trunk and the legs.

■ Extinction. Simultaneously stimulate corresponding areas on both sides of the body. Ask where the patient feels your touch. Normally both stimuli are felt.

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