Anismus is known by a number of other medical names including ‘pelvic floor dyssynergia’ and ‘paradoxical puborectalis contraction’.

During a bowel motion, the external anal sphincter (the voluntary muscle at the anus that you can control) and the puborectalis muscle (an internal muscle which forms part of the pelvic floor) should relax, allowing stool to pass. In people with anismus these muscles do not relax and bowel opening is not properly co-ordinated. This can cause severe difficulty in initiating bowel movements, feelings of incomplete emptying and is one of the causes of obstructed defaecation syndrome.


It is often not completely clear why anismus occurs. It can be due to spasms as a result of fissure, trauma to the anus, haemorrhoids or rectal prolapse. Very occasionally there can be an abnormality of the external sphincter muscle. Often no apparent physical cause is found. Stress is a very important aggravating factor in anismus.


The diagnosis of anismus is based on clinical examination, anorectal physiology and defaecating proctography

Probably the best diagnostic test for anismus is a positive response to injection of botulinum toxin.


Some patients report improvement in their symptoms with pelvic floor retraining. This treatment, which combines tailored lifestyle and dietary advice together with muscle retraining (help to improve co-ordination of muscles during defecation) can be of great benefit, though not everybody finds it useful.

Surgical treatment can often be helpful, and we usually recommend an injection of botulinum toxin into the pelvic floor muscles. This causes a temporarily relaxation of the muscles, allowing normal bowel opening to be regained. If successful, the initial injection can relieve symptoms up to twelve weeks. The injection can be repeated and the second injection usually lasts longer and may be permanent.

If the botulinum toxin fails, there may be an underlying prolapse. During an examination under anaesthetic your surgeon will be able to exclude or confirm this, and treatment of underlying problems will be recommended.

Please be advised that the information on this website is not a substitute for professional medical advice, diagnosis or treatment