Anismus

What is anismus?
Anismus is known by a number of other medical names including pelvic floor dyssynergia and paradoxical puborectalis contraction. It refers to a condition in which the external anal sphincter and the puborectalis muscle contracts rather than relaxes during an attempted bowel motion. It is one of the causes of obstructed defaecation syndrome (ODS).

What causes anismus?
It is not completely clear why anismus occurs in patients. It is probably a specific voluntary sphincter muscle abnormality.

What symptoms does anismus cause?
Patients often report symptoms of constipation. They often have to strain when trying to pass a stool and that they get a sensation of a blockage or resistance to passing a stool.

How is it diagnosed?
The diagnosis of anismus is based on clinical examination, anorectal physiology and proctography. More sophistication evaluation (simultaneous needle electromyography and defaecating proctography) is said to be needed for the diagnosis but we believe this to be questionable. Probably the best diagnostic test for anismus is a positive response to botulinum toxin.

How is anismus treated?
Some patients will report improvement in their symptoms with biofeedback, which retrains the muscles, helping the patient to relax the sphincter muscle during defaecation. We usually recommend an injection of botulinum toxin into the sphincter muscle after giving a local anaesthetic block to numb sensation. If successful, the initial injection relieves symptoms for about 6 weeks then begins to wear off. The injection can be repeated and the second injection usually lasts longer and may be permanent. If the botulinum toxin fails, there is usually underlying prolapse not shown on proctography, and an examination under anaesthetic will be arranged to confirm this.