The internal anal sphincter in systemic sclerosis

Fecal incontinence in systemic sclerosis can occur secondary to fibrous replacement of the internal sphincter or ischemic myopathy of internal anal sphincter from vasculitis. Both lead to morphologic changes of the internal anal sphincter on endoanal ultrasound. This study documents the morphologic changes that can occur.

A retrospective study of consecutive patients with systemic sclerosis and fecal incontinence was performed. Endoanal ultrasound was performed by using a 10 MHz Bruel and Kjaer endoprobe. Internal anal sphincter thickness and echogenecity were assessed at mid anal canal using prospectively collected images. Sphincter thicknesses were measured at 3, 6, 9, and 12 o'clock positions and averaged. Sphincter quality was assessed as homogeneous or heterogeneous and hyperechoic or hypoechoic by an experienced colorectal surgeon. Sphincter thickness was compared with sex- and age-matched controls by using Wilcoxon's signed-rank test.

There were 11 patients (all women). Two distinct morphologic changes were observed where patients had a thickened, homogeneous, and hypoechoic internal anal sphincter, or a thinned, difficult to discern, and hyperechoic internal anal sphincter. Average sphincter thickness was 1.6 (range, 0.8-4) mm, which was significantly different from control subjects (P = 0.028).

Available literature suggest that internal anal sphincter in systemic sclerosis is invariably thinned and hyperechoic. This series suggests that two distinct morphologic changes are possible.