Patients may complain of either lost or abnormal sensations. The term "numbness" is often used by patients to denote loss of feeling, but the word also has other meanings and the patient's intention must be clarified. Abnormal spontaneous sensations are generally called paresthesias, and unpleasant or painful sensations produced by a stimulus that is usually painless are called dysesthesias.
Sensory symptoms may be due to disease located anywhere along the peripheral or central sensory pathways (eFigure 24–1). The character, site, mode of onset, spread, and temporal profile of sensory symptoms must be established and any precipitating or relieving factors identified. These features—and the presence of any associated symptoms—help identify the origin of sensory disturbances, as do the physical signs as well. Sensory symptoms or signs may conform to the territory of individual peripheral nerves or nerve roots. Involvement of one side of the body—or of one limb in its entirety—suggests a central lesion. Distal involvement of all four extremities suggests polyneuropathy, a cervical cord or brainstem lesion, or—when symptoms are transient—a metabolic disturbance such as hyperventilation syndrome. Short-lived sensory complaints may be indicative of sensory seizures or cerebral ischemic phenomena as well as metabolic disturbances. In patients with cord lesions, there may be a transverse sensory level. Dissociated sensory loss is characterized by loss of some sensory modalities with preservation of others. Such findings may be encountered in patients with either peripheral or central disease and must therefore be interpreted in the clinical context in which they are found.
Sensory pathways conveying touch, pressure, vibration, joint position, pain, and temperature sensation. (Reproduced, with permission, from Simon RP, Aminoff MJ, Greenberg DA. Clinical Neurology, 4th ed. Originally published by Appleton & Lange. Copyright © 1999 by The McGraw-Hill Companies, Inc.)
The absence of sensory signs in patients with sensory symptoms does not mean that symptoms have a nonorganic basis. Symptoms are often troublesome before signs of sensory dysfunction have had time to develop.