Anismus is a medical condition that involves the malfunction of the external anal sphincter and the puborectalis muscle, whereby they experience a paradoxical, or extreme, contraction. Such a defect of these muscular fibers hampers defecation, which is the final stage of digestion, involving expelling feces through the anus. Anismus is known by five other terms: anal sphincter dyssynergia, dyssynergic defecation, paradoxal puborectal contraction, pelvic floor dyssynergia and spastic pelvic floor syndrome. Anismus is most common in women and young children.
The external anal sphincter, also known as the sphincter ani externus, is an egg-shaped structure usually measuring about 3 inches (8 cm) or 4 inches (10 cm). Positioned about 1 inch (approximately 2.5 cm) from the anus, it contributes to the protection of the opening's margins. A few inches above it is the puborectalis, or sphincter recti, which helps to form a sling around the final part of the intestine before it terminates at the part of the anus called the rectum. Its relaxation, along with other parts such as the external anal sphincter, cuts down the angle between the rectum and anus to permit defecation.
Currently, medical researchers offer a variety of reasons for the occurrence of anismus. The condition shows up in people who have Parkinson's disease. This led to a 1988 report published in the Journal of Neurology, Neurosurgery, and Psychiatry that theorizes that anismus can be classified as focal dystonia. This means that it can be caused by a neurological condition characterized by involuntary muscular contraction. Others suggest that anismus can be blamed on sexual abuse, specifically, intercourse by inserting the penis in the anus instead of the vagina.
Moreover, anismus is more likely to appear in people with certain rectal problems. This includes rectal ulcers, or sores; and rectal prolapse, which involves protrusion of the rectum through the anus. With women in particular, the condition could show up with rectocele, which is characterized by a tear in the thin structure separating the rectum and vagina called the rectrovaginal septum.
Some medical professionals, however, have questioned the clinical significance of anismus. Many people with malfunction of the external anal sphincter do not develop the condition. Moreover, a 1998 report, the result of a study conducted at University Hospital Rotterdam-Dijkzigt in the Netherlands, discounted the malfunction of the puborectalis muscle as a major cause of anismus. Without addressing the issue, however, with medical techniques such as surgical resection, biofeedback training or Botox injections, anismus can cause constipation. This often leads to an enlargement of the rectum brought about by fecal impaction, which involves the trapping of hardened feces in the organ. In some cases, patients may experience encopresis, which is involuntary fecal passing.