[Usefulness of electromyographic techniques of the bulbocavernosus muscle in the diagnosis of neurogenic impotence].

OBJECTIVE: To analyze the utility of electromyographic study of the bulbocavernosus muscle.

METHODS: 126 impotent patients were evaluated by physical examination and neuroandrologic profile. The physical examination consisted in an exploration of the anal tone and the bulbocavernosus reflex. The neuroandrologic profile consisted in selective electromyography of the bulbocavernosus muscle, the determination of the S2-S4 evoked potentials, somatosensory potential of the pudenal nerve, electromyography of cavernous smooth muscle (SPACE) sympathetic skin response and cystometry.

RESULTS: The results of the bulbocavernosus electromyography and S2-S4 evoked potentials were different from the data obtained from the physical examination of the anal tone and the bulbocavernosus reflex. Selective bulbocavernosus electromyography showed a sensitivity of 57% and a specificity of 84%. The S2-S4 evoked potentials showed a sensitivity of 61% and a specificity of 100%. The diagnostic value of the S2-S4 evoked potentials increased at 39 msec cutoff (sensitivity = 66%; specificity = 95%). Exploration of the anal tone is very specific for neurologic lesion in impotence (93%), but has a low sensitivity (30%). The clinical bulbocavernosus reflex showed a good specificity (85%) and sensitivity (75%) in the diagnosis of pudendal efferent lesion, but is less useful in the diagnosis of neurogenic impotence.

CONCLUSIONS: The highest diagnostic value was obtained with the S2-S4 evoked potentials. Selective electromyography of the bulbocavernosus muscle showed a moderate diagnostic value. Physical examination of peripheral pudendal innervation does not appear to be useful for screening for neurologic lesion in impotence because of its low sensitivity, which may be due to existing incomplete nervous lesions.