Relationship between penile thermal sensory threshold measurement and electrophysiologic tests to assess neurogenic impotence

Objectives. Erectile function is usually assessed by neurophysiologic tests such as the bulbocavernosus reflex or pudendal nerve somatosensory evoked potentials. These tests investigate only large nerve fibers, although erect ion depends on autonomic nerve fibers, which are of small diameter. Warm an d cold sensory fibers have similar calibers as the autonomic nerve fibers, and their integrity can be reliably evaluated by the measurement of thermal sensory thresholds. We studied penile thermal sensory testing in parallel with standard electrophysiologic tests to assess their sensitivity in the d iagnosis of penile neuropathy. Methods. Twenty-five normal male subjects without erectile dysfunction or e vidence of diffuse neuropathy (group 1) and 35 diabetic patients who compla ined of impotence (group 2) were studied. Erectile function was quantitated using the erectile dysfunction symptom score. Warm, cold, and vibratory se nsory thresholds were assessed on the dorsal aspect of the penis. In additi on, penile sympathetic skin responses and pudendal nerve somatosensory evok ed potentials were recorded. Results. We found a significant difference between the two groups in the er ectile dysfunction symptom score (P < 0.0001), cold threshold (P = 0.0007), and warm threshold (P = 0.0025), but not for the other parameters. The ere ctile dysfunction symptom score correlated with the penile warm and cold th resholds (P = 0.0006 and 0.002, respectively). Conclusions. Thermal thresholds assess small nerve fiber damage, which can indirectly reflect autonomic disturbances, particularly in the context of a diffuse neuropathy such as diabetic polyneuropathy. Penile thermal sensory testing correlated strongly with the clinical evaluation of erectile funct ion and is a new and promising tool for the diagnosis of neurogenic impoten ce. UROLOGY 57: 306-309, 2001. (C) 2001, Elsevier Science Inc.