In the axonal polyneuropathies, sensation is affected symmetrically in the distal segments of the limbs and more in the legs than in the arms, owing to the length-dependent nature of most diseases that affect peripheral nerves. In most types, all sensory modalities (touch-pressure, pain and temperature, vibratory and joint position senses) are impaired or eventually lost, although one modality is often affected disproportionately to the others; for example, temperature sensation (small afferent fibers) may be impaired more than joint position and vibration (larger fibers). As an axonal neuropathy worsens, there is spread of sensory loss from the distal to more proximal parts of the limbs and eventually, to the anterior abdomen, thorax, and the face. An “escutcheon” pattern of sensory loss over the anterior abdomen and thorax in severe axonal neuropathy may be mistaken for the sensory level of a spinal cord lesion if the back is not examined. Another characteristic form of sensory loss affects the trunk, scalp, and face and later, the trunk and limbs; this is the pattern of a sensory ganglionopathy that is the result of simultaneous dysfunction of all parts of the sensory nerve.
Most often, universal sensory loss is attributable to an acquired disease affecting the sensory ganglia (sensory neuronopathy); a paraneoplastic process or certain toxic or immune diseases are usually responsible (e.g., Sjögren disease, scleroderma).
Paresthesias, Pain, and Dysesthesias
These symptoms were described in Chaps. 7 and 8. Sensory symptoms tend to be especially marked in the hands and feet. “Pins and needles,” “falling asleep,” “stabbing,” “tingling,” “prickling,” “electrical,” and “Novocain-like” are the adjectives chosen by patients to describe these positive sensory experiences. In some neuropathies, paresthesias and numbness are the only symptoms and objective sensory loss is lacking or minimal. Certain neuropathies characteristically cause pain, which is described as burning, aching, sharp and cutting, or crushing and at times may resemble the lightning pains of tabes dorsalis. Perversion of sensation (allodynia) is also commonplace in some polyneuropathies—for example, tingling, burning, stabbing pain, or just an uncomfortable dysesthesia is induced by tactile stimuli. Under these conditions a stimulus induces not only an aberrant sensation but also one that radiates to adjacent areas and persists after the stimulus is withdrawn. As remarked in Chap. 8, the reactions of a patient with allodynia may seem to indicate hypersensitivity (“hyperesthesia”), but more often the sensory threshold is actually raised and it is the sensory experience or response that is exaggerated (hyperpathia).
Painful paresthesias and dysesthesias are particularly common in diabetic, alcoholic–nutritional, and amyloid neuropathies. Mainly they affect the feet (“burning feet”) and less often the hands. In herpes zoster, they are confined to dermatomal regions of the body. A particularly intense form of burning pain typifies the causalgia of a partial nerve lesion (usually traumatic) of the ulnar, median, posterior tibial, peroneal, or occasionally some other nerve (see Chap. 7 and further on in this chapter).