A 74-year-old man comes to the office due to chronic constipation. Bowel movements occur once every 3 days and are hard and pellet-like. The patient frequently strains when he tries to defecate and never feels completely evacuated. The constipation is occasionally so severe that he uses his fingers to remove stool from the anorectal vault. Medical history is significant for Parkinson disease, for which he takes carbidopa-levodopa. Vital signs are unremarkable. A resting tremor is present on physical examination. The abdomen is distended but nontender to palpation. This patient's condition is most likely due to inadequate relaxation of which of the following muscles during defecation?

Question

A 74-year-old man comes to the office due to chronic constipation.  Bowel movements occur once every 3 days and are hard and pellet-like.  The patient frequently strains when he tries to defecate and never feels completely evacuated.  The constipation is occasionally so severe that he uses his fingers to remove stool from the anorectal vault.  Medical history is significant for Parkinson disease, for which he takes carbidopa-levodopa.  Vital signs are unremarkable.  A resting tremor is present on physical examination.  The abdomen is distended but nontender to palpation.  This patient's condition is most likely due to inadequate relaxation of which of the following muscles during defecation?

Quizplus · Accepted Answer

Stool continence is largely maintained by tonic contraction of the internal and external anal sphincter and the puborectalis muscle, which forms a muscular sling around the rectum and squeezes it into a narrow angle to prevent stool leakage. Defecation requires the coordinated relaxation of these muscles, which occurs as follows: Distension of the rectal vault activates mechanoreceptors that cause involuntary relaxation of the internal anal sphincter (rectosphincteric reflex) and an urge to defecate. The puborectalis muscle and external anal sphincter are under voluntary control; when defecation is desired, the muscles relax and the rectum contracts, expelling feces. The abdominal muscles contract to increase the pressure gradient of the rectum and aid in the rapid expulsion of feces. If the internal or external anal sphincter or, more commonly, the puborectalis muscle fails to relax, stool remains in the rectal vault despite attempts to initiate bowel movements (dyssynergia), resulting in chronic constipation. Patients often strain for a long time only to pass small amounts of stool, and manual disimpaction may be required. Dyssynergic defecation is usually considered a functional disorder and occurs more commonly in the elderly; however, it can occur with certain neurologic disorders (eg, Parkinson disease, multiple sclerosis) or trauma. (Choice A) The bulbospongiosus is a superficial perineal muscle that enables penile erection and ejaculation in men and facilitates both vaginal canal closure and orgasm in women. Its dysfunction would lead to sexual impairment but not defecatory dysfunction. (Choices B and C) The obturator internus and externus and the piriformis contribute to lateral hip rotation. Dysfunction in these muscles would result in motor impairment and gait abnormalities, not defecatory dysfunction. (Choice E) The rectus abdominis consists of 2 large, paired muscles that run vertically along the anterior abdominal wall. Contraction of abdominal muscles increases the pressure gradient of the rectum and aids in the rapid expulsion of feces; failure of this muscle to relax would not result in constipation. Educational objective: Dyssynergic defecation occurs when the puborectalis muscle or the internal or external anal sphincter fails to relax during defecation, leading to chronic constipation. Dyssynergic defecation is usually considered a functional disorder and occurs more commonly in the elderly but may also occur with certain neurologic disorders (eg, Parkinson disease, multiple sclerosis) or trauma. __________ References: Constipation in neurological diseases. (http://www.ncbi.nlm.nih.gov/pubmed/12486259) Management of constipation in patients with Parkinson's disease. (http://www.ncbi.nlm.nih.gov/pubmed/29560414)

A 74-Year-Old Man Comes to the Office Due to Chronic