On the nature of nondermatomal somatosensory deficits.

OBJECTIVES: Nondermatomal somatosensory deficits (NDSDs) not conforming to the distribution of peripheral nerves or dermatomes, and often present after a minor injury or with no known inciting event, have long been associated with "hysteria." This article reviews the modern literature concerning NDSDs associated with chronic pain with regard to their prevalence, phenomenology and clinical presentation, clinical assessment, etiology and pathophysiology, relationship with Conversion Disorder and psychological factors, and their treatment and prognosis.

METHODS: Past research and relevant literature concerning NDSDs are reviewed and summarized. Clinical case reports are presented to illustrate the salient features of NDSDs.

RESULTS: The prevalence of NDSDs varies between 25% and 50% in samples of chronic pain populations. We describe the temporal, spatial, qualitative, motor, sensory, and behavioral characteristics of NDSDs. Illustrative case reports show the remarkable NDSD phenomenology, variability, and reversibility. NDSDs represent intensely dynamic phenomena that are likely associated with supraspinal mechanisms. Recent functional imaging findings show significant alterations in brain activation patterns in these patients. Similar but spatially and temporally restricted phenomena have been shown in experimental studies with healthy controls and pain patients. NDSDs are associated with certain demographic variables, and possibly psychological factors seem to constitute a poor prognostic sign for response to treatment and return to work and can coexist with structural musculoskeletal or nervous system abnormalities.

CONCLUSIONS: NDSDs are important and prevalent clinical phenomena associated with chronic pain. Their prevalence in the general population, primary care settings, and non pain patients is unknown. Research needs to be carried out to elucidate these important phenomena.