Functional sensory symptoms

Functional (psychogenic) sensory symptoms are those in which the patient genuinely experiences alteration or absence of normal sensation in the absence of neurologic disease. The hallmark of functional sensory symptoms is the presence of internal inconsistency revealing a pattern of symptoms governed by abnormally focused attention. In this chapter we review the history of this area, different clinical presentations, diagnosis (including sensitivity of diagnostic tests), treatment, experimental studies, and prognosis. Altered sensation has been a feature of "hysteria" since descriptions of witchcraft in the middle ages. In the 19th century hysteric sensory stigmata were considered a hallmark of the condition. Despite this long history, relatively little attention has been paid to the topic of functional sensory disturbance, compared to functional limb weakness or functional movement disorders, with which it commonly coexists. There are recognizable clinical patterns, such as hemisensory disturbance and sensory disturbance finishing at the groin or shoulder, but in keeping with the literature on reliability of sensory signs in neurology in general, the evidence suggests that physical signs designed to make a positive diagnosis of functional sensory disorder may not be that reliable. There are sensory symptoms which are unusual but not functional (such as synesthesia and allochiria) but also functional sensory symptoms (such as complete loss of all pain) which are most unusual and probably worthy of independent study.