The role of polysomnography in the differential diagnosis of chronic insomnia.

The authors examined the accuracy of the differential diagnosis of chronic insomnia with and without sleep laboratory studies in a consecutive series of 123 patients. All patients were evaluated by means of a sleep/wake log, a sleep habits questionnaire, structured psychiatric and clinical interviews, and a minimum of two consecutive nights of polysomnography. Notwithstanding a high rate of Research Diagnostic Criteria (RDC)-diagnosed psychopathology (63%) in this sample, the major finding was that in 49% of the patients laboratory results added to, refuted, and/or failed to support the clinical impression. This resulted in substantial modification of the initial diagnostic formulation and therefore in increased specificity of diagnosis.