D2I2.
common

Anismus

Anismus or dyssynergic defecation is the failure of normal relaxation of floor muscles during attempted defecation. It can occur in both children and adults, and in both men and women. It can be caused by physical defects or it can occur for other reasons or unknown reasons. Anismus that has a behavioral cause could be viewed as having similarities with parcopresis, or psychogenic fecal retention.

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Plain-language summary adapted from Wikipedia. Not medical advice.