Interference pattern in perineal muscles. A quantitative electromyographic study in patients with faecal incontinence.

The aim of this study was to investigate the possibility of neuromuscular dysfunction in patients with faecal incontinence by measuring interference patterns in the external anal sphincter and puborectalis muscles with quantitative electromyography. The design was an open study including 20 patients with faecal incontinence; in 14 the aetiology was idiopathic and 6 had rupture of the external anal sphincter. Electromyographic interference patterns (turns/amplitude analysis) measured at rest and during maximum voluntary contraction in all patients were recorded together with fibre density measured by single fibre electromyography (n = 10) and anal pressure measured at rest and at maximum contraction (n = 17). A comparison was made with results of a previously published series of reference values taken from normal volunteers. The density of the interference pattern on maximum contraction of the puborectalis muscle was significantly lower among the patients with idiopathic faecal incontinence than among the reference group (137 compared with 241 turns/second, p < 0.01). There was also a significant difference on maximum contraction of the anal sphincter muscle among the group in whom it was ruptured compared with the reference group (76 compared with 165 turns/second, p < 0.05). Fibre density increased with age and was significantly higher among those with idiopathic incontinence (1.64 (0.2) compared with 1.33 (0.1) in the reference group, p < 0.01). There were no significant differences in anal manometry measurements between the groups. In conclusion, in patients with faecal incontinence the role of central activation of the perineal muscles is important, though other factors may play a part.