Anismus, also known as puborectalis syndrome, is paradoxical contraction of the external anal sphincter during attempted defecation, leading to fecal retention and a complaint of constipation. This may occur as an idiopathic condition in isolation, or as a feature of the off periods of idiopathic Parkinson’s disease. It is thought to represent a focal dystonia, and may be helped by local injections of botulinum toxin.
Jost WH, Muller-Lobeck H, Merkle W. Involuntary contractions of the striated anal sphincters as a cause of constipation: report of a case. Diseases of the Colon and Rectum 1998; 41: 258-260