2. Segmentary type: ganglionary, radicular and segmental-dissociated.
3. Central: conduction, central, cortical.
4. Symptoms of loss and irritating signs (sensitive "Jackson").
Examination. Somatic sensation is tested with the patient’s eyes closed and on the symmetrical parts of body. The appreciation of sense of light touch is evaluated with a wisp of cotton wool, which is brought down carefully on a small region of skin. The patient lies quietly, with the eyes closed, and makes a signal each time the stimulus is felt. General tactile sensibility is tested by the use of a light stimulus such as a camel's hair brush, a wisp of cotton, a feather, a piece of tissue paper, or even a very light touch with a fingertip. Touch is tested along with pain by stimulating alternately (but not in an even rhythm) with the sharp and blunt portions of a pin. The stimulus should be so light that no pressure on subcutaneous tissues is produced. Allowance must be made for thicker skin on the palms and soles and the especially sensitive skin in the fossae. The patient is asked to say «Now» or «Yes» when he feels the stimulus and to name or point to the area stimulated and state the nature of the stimulus. Similar stimuli are used for evaluating discriminatory tactile sensation but this is best tested on the hairless skin, since motion of the hairs must be avoided. It is also tested by noting the patient's ability to localize the stimuli accurately and by investigating two-point discrimination. Topoanesthesia may be used to indicate loss of tactile localization. Graphanesthesia is the inability to recognize numbers or letters written on the skin. Pressure sensation, or touchpressure, may be regarded as a distinct type of tactile sensation, involving more gross pressure from the skin. Pressure sense is tested by firm touch upon the skin with a finger or a blunt object, and by pressure on the subcutaneous structures, such as the muscle masses, the tendons, and the nerves themselves, either by the use of a blunt object or by squeezing between the fingers, and one tests both the appreciation and the localization of pressure. Two-point, or spatial, discrimination is the ability to differentiate cutaneous stimulation by one blunt point from stimulation by two points. A compass or a calibrated two-point esthesiometer is used, and the patient is stimulated randomly by a single point and by two points. The distance varies considerably in different parts of the body. Two points can be differentiated from one at a distance of 1 mm on the tip of the tongue, at 2 - 4 mm on the fingertips, at 4 - 6 mm on the dorsum of the fingers, at 8-12 mm on the palm, and at 20 - 30 mm on the dorsum of the hand. Two-point discrimination is a highly discriminatory tactile sensibility, carried mainly through the posterior columns (dorsal funiculi). Loss of two-point discrimination with preservation of other discriminatory tactile and proprioceptive sensation may be the most subtle sign of a lesion of the opposite parietal lobe. Barognosis is the recognition of weight, or the ability to differentiate between weights. It is tested by the use of objects of similar size but of different weights, such as a series of plastic or wooden balls, or blocks loaded with different weights, which are appraised by holding them in the hand, either unsupported or resting on a table, but preferably the former. The senses of motion and position should be intact. Pinprick appreciation is tested by asking the patient to indicate whether the point of a pin feels sharp or blunt. Appreciation of sense of pressure or sense of touch by the pinpoint must not be confused with the appreciation of sharpness. Temperature sensation is evaluated by application to the skin of containers of hot or cold water or, better, by the use of cold or warm metal tubes or other metal objects. The patient is asked to respond by saying «hot» or «cold». Changes in temperature sensibility are recorded by the terms thermanesthesia, thermhypesthesia, and thermhyperesthesia, modified by the adjectives hot and cold. Deep pressure sensibility is evaluated by pressure on the tendons, such as the Achilles tendon at the ankle. Sense of vibration is evaluated with a tuning fork (128 Hz) that is set in motion and then placed over a bony prominence; the patient is asked to indicate whether vibration, rather than simple pressure, is felt. Joint position sense is tested by asking the patient to indicate the direction of small passive movements of the terminal interphalangeal joints of the fingers and toes.
Sensations of motion and position may also be tested by placing the fingers of one of the patient's hands in a certain position while his eyes are closed, then asking him to describe the position or to imitate it with the other hand. The foot may be passively moved while the eyes are closed, and the patient asked to point to his great toe or his heel. The patient may be asked to hold his hands outstretched; with loss of position sense one hand may waver or droop. One of the outstretched hands may be passively raised or lowered while the patient's eyes are closed, and the patient is asked to place the other extremity at the same level. One of the hands may be passively moved while the eyes are closed, and the patient asked to grasp the thumb or forefinger of that hand with the opposite hand. These latter tests, however, do not denote the side of involvement when a unilateral lesion is present.
Certain tests for ataxia, such as the finger-to-nose test and the heel-to-knee-to-toe test, are methods for examining the senses of motion and position if they are executed while the eyes are closed, assuming the tests are normal when the eyes are open. The senses of motion and position are also examined by observation of the station and gait. A patient with significantly disturbed sensations of movement and of position in the lower extremities is not aware of the position of his feet or of the posture of his body. A patient can assume a stable, erect posture when standing with his eyes open, but when his eyes are closed he tends to sway and fall; he can walk fairly well when his eyes are open, but when his eyes are closed he throws out his feet, staggers, and may fall (sensory ataxia). The Romberg sign is positive when the patient is able to stand with his feet together while his eyes are open, but sways or falls when they are closed; it is one of the earliest signs of posterior column disease.
Figure 3.2 Segmental innervation of the skin (A.A. Skoromets,1995)
