Theoretical and technical problems in the measurement of nocturnal penile tumescence for the differential diagnosis of impotence.

Theoretical and technical problems in using Nocturnal Penile Tumescence (NPT) measurements for the differential diagnosis of impotence are discussed and possible solutions are offered: 1) The basic assumption that NPT measurements can distinguish psychogenic from organic impotence has never been demonstrated in patients shown to be psychogenically and organically impotent independent of the NPT measurements themselves. Studies attempting to do this are necessary to determine definitively the limits of the clinical applicability of this important diagnostic tool. 2) Evidence is presented showing that though a direct observation of one of the patient's fullest erections is required for an adequate NPT evaluation, this is not always done. The danger of misdiagnosis if this step is omitted is illustrated with a case report. 3) Disagreements in the literature about NPT criteria for diagnosing psychogenic impotence are discussed and criteria are suggested that are based on demonstrating the intactness of the physiological mechanisms required for erection rather than on values recorded in normal subjects.