INVOLVEMENT OF THE EXTERNAL ANAL-SPHINCTER IN AMYOTROPHIC-LATERAL-SCLEROSIS

In amyotrophic lateral sclerosis the striated pelvic floor sphincter m uscles are functionally uninvolved, and pathological studies have conf irmed the relative resistance of the Onuf nucleus motor neurons. We ha ve evaluated the external anal sphincter (EAS) muscle in 16 patients w ith ALS using single fiber EMG, and compared the results with the find ings in the semimembranosus-semitendinosus (SM-ST) muscles that have i nnervation from the L-5, S-1, and S-2 segments. The results were compa red with a group of controls matched for age and sex. None of the pati ents or controls had symptomatic sphincter involvement and none of the 4 women studied were parous. Eight patients with ALS showed an increa sed fiber density in the EAS; 6 had an abnormal neuromuscular jitter. In 1 there was fibrillation in the EAS. In the SM-ST muscle 11 patient s showed an increased fiber density, and 7 had an abnormal neuromuscul ar jitter. In 3 patients with ALS in whom there were abnormal findings in the EAS the bulbocavernosus reflex and pudendal nerve evoked poten tials were normal. Neurogenic change was more marked in the SM-ST than in the EAS muscle. These findings show that the EAS is not normal in ALS. However, the relative resistance of the EAS to ALS is sufficient to prevent incontinence, even in the longer-surviving older patients. (C) 1995 John Wiley and Sons, inc.