The relationship between internal rectal prolapse and internal anal sphincter function

Aim Faecal incontinence is commonly seen in patients with internal rectal prolapse (IRP), although the mechanism is not clear. This study assessed the relationship between IRP and anal sphincter function. Method Patients both with IRP diagnosed on proctography and those with external rectal prolapse (ERP) were identified from a prospective database generated from a tertiary referral pelvic floor clinic. The results of anorectal manometry were analysed, and the relationship between sphincter pressure and grade of prolapse was assessed. Results A total of 515 patients were identified with clinical evidence of ERP or proctographic evidence of internal and external prolapse. There were 88 with grade 5 or external prolapse [mean maximal resting pressure (MRP) 28.5 (standard error 2.1) mmHg], 156 with grade 4 prolapse [44.0 (1.8) mmHg], 153 with grade 3 prolapse [49.2 (1.6) mmHg], 88 with grade 2 prolapse [56.2 (2.1) mmHg] and 29 patients with grade 1 rectal prolapse [56.8 (4.5) mmHg]. There was a significant reduction in the mean MRP with increasing grade of prolapse from grade 2 to 5. By contrast, there was no relationship between prolapse grade and mean maximal squeeze pressure, except in patients with ERP, in whom the squeeze pressure was significantly lower compared with patients with IRP. Conclusion This is the first large-scale study to show the relationship between internal prolapse and MRP. The observation that squeeze pressure is unchanged suggests that the effect of internal prolapse on continence occurs mainly through a reduction in internal anal sphincter tone.