Anal sphincter electromyography: Needle examination in the diagnosis of fecal incontinence

Introduction: Fecal incontinence is usually attributed to pelvic floor denervation of striated muscle or direct sphincter trauma. Diagnosis of the anal sphincter defects are usually made by palpation and confirmed either by supportive evidence from manometry, anal endosonography, or more directly by electromyography (EMG).

Objectives: The EMG examination of the external anal sphincter (EAS) muscles is helpful in diagnosing the extent of neurogenic involvement. This technique was applied in a systematic quantitative manner in our department, and it is a very practical examination in any EMG laboratory.

Methods: Fifty-six patients with fecal incontinence were studied. A group of 33 women and 23 men participated in this study. Their mean age was 53 years (range, 36–78 years). Conventional nerve conduction studies of the posterior tibial and sural nerves, H reflex (S1), and F waves were performed. Quantitative EMG of the lower limbs muscles was performed before the EAS muscles. In some cases, Strumpell phenomenon was a helpful tool in pyramidal syndrome diagnosis. EAS motor unit action potentials (MUAPs) and interference pattern were analyzed.

Results: Previous studies had shown that a mean prolongation of the MUAPs duration is the most important measurement to identify changes of chronic reinnervation in the sphincter.

Conclusions: The results suggest that anal sphincter EMG, when performed together with the nerve conduction study protocol used by our department, including the Strumpell phenomenon, is an accessible method to evaluate not only lower sacral segments but other systemic disorders.

M.R. Kai and J.L. Alonso Nieto
São Paulo, Brazil