The role of nocturnal penile tumescence in differentiating between organic and psychogenic impotence: the first stage of validation.

A study was conducted to assess the validity of nocturnal penile tumescence (NPT) as a means of distinguishing between psychogenic and organic erectile failure (impotence). On the basis of independent clinical criteria, patients were assigned to one of four diagnostic categories--organic impotence, psychogenic impotence, mixed etiology, and uncertain etiology. The NPT characteristics of the patients in the organic and psychogenic groups were compared and decision rules formulated in order to provide optimal discrimination between the two diagnostic categories. A decision rule based on the maximum erectile response observed for each patient led to the correct diagnosis in 80% of cases. Accuracy was increased to 95% when a decision rule based on the maximum frequency of nocturnal erections was employed. The clinical value and limitations of NPT as a diagnostic procedure are discussed.