Electromyography of the external urethral sphincter in patients with prostatic hyperplasia.

We analyzed quantitatively the action potential of external urethral sphincter muscles by electromyography in 9 patients with benign prostatic hyperplasia and in 13 patients without micturition disturbances. In patients with benign prostatic hyperplasia the motor unit potentials had a mean amplitude of 290 plus or minus 40 microV., duration 5.0 plus or minus 0.1 msec. and phases 3.9 plus or minus 0.1. The control group values were 310 plus or minus 20 microV., 5.5 plus or minus 0.1 msec. and 3.8 plus or minus 0.1, respectively. There was a significant difference in duration, which was probably due to the difference in age of the 2 groups. An inverse relationship between age and duration was proved in the patients examined.