Combined uroflowmetry and external sphincter electromyography studies were done both preopera- tively and postoperatively in patients with benign prostatic hyperplasia. In 56 patients preoperative electromyography during voiding showed silent or markedly suppressed activity in 41 patients (73.2%), while the remaining 15 patients (27.8%) revealed active electromyography. In the postoperative studies, 12 patients revealed active electromyography even after the release of obstruction. The urine flow rate following operation was not drastically improved in the active electromyography group compared to the silent electromyography group. We suppose that long-term urethral obstruction with prostatic adenoma could influence the function of relaxation of the external sphincter muscle in some patients with benign prostatic hyperplasia.
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