A 72-year-old man comes to the emergency department due to a 24-hour history of progressive lower abdominal discomfort and difficulty voiding. The patient has never had urinary difficulty in the past. He has a history of hypertension, ischemic stroke with mild left-sided residual weakness, and a recent episode of abdominal shingles. The patient also reports several days of non-productive cough and has been taking over-the-counter diphenhydramine for 2 days. He is a former smoker and does not drink alcohol. Temperature is 36.7 C (98 F), blood pressure is 150/80 mm Hg, and pulse is 105/min. The patient appears restless. Bilateral breath sounds are normal with no added sounds. Cardiac examination reveals regular rhythm. Previous area of shingles on the abdominal wall has no active lesions but the area is hyperesthetic. There is suprapubic fullness and tenderness. A mildly enlarged, nontender prostate is palpated on the rectal examination. Which of the following is the most likely cause of this patient's current condition?

Question

A 72-year-old man comes to the emergency department due to a 24-hour history of progressive lower abdominal discomfort and difficulty voiding.  The patient has never had urinary difficulty in the past.  He has a history of hypertension, ischemic stroke with mild left-sided residual weakness, and a recent episode of abdominal shingles.  The patient also reports several days of non-productive cough and has been taking over-the-counter diphenhydramine for 2 days.  He is a former smoker and does not drink alcohol.  Temperature is 36.7 C (98 F), blood pressure is 150/80 mm Hg, and pulse is 105/min.  The patient appears restless.  Bilateral breath sounds are normal with no added sounds.  Cardiac examination reveals regular rhythm.  Previous area of shingles on the abdominal wall has no active lesions but the area is hyperesthetic.  There is suprapubic fullness and tenderness.  A mildly enlarged, nontender prostate is palpated on the rectal examination.  Which of the following is the most likely cause of this patient's current condition?

Quizplus · Accepted Answer

This elderly patient with difficulty voiding and a palpable lower abdominal mass (likely representing an overfilled bladder) has acute urinary retention due to an adverse effect of diphenhydramine. First-generation H1-antihistamines (eg, diphenhydramine, chlorpheniramine, hydroxyzine) also have significant anticholinergic effects (eg, at muscarinic receptors of the parasympathetic nervous system), which can manifest as dryness of the eyes, dryness of the oral mucosa and respiratory passages, or urinary retention. Urinary retention caused by anticholinergic agents results from impaired detrusor muscle contraction and, to a lesser extent, impaired internal sphincter relaxation, both of which are controlled by parasympathetic input from the pelvic splanchnic nerves. Elderly men, who are likely to have some degree of underlying urinary obstruction due to benign prostatic hyperplasia (BPH), are at increased risk of developing urinary retention due to anticholinergic agents. (Choice A) The abdominal musculature may be used in an accessory fashion to increase intraabdominal pressure and facilitate urination or defecation; however, a solitary defect in the strength of the abdominal musculature would be insufficient to cause urinary retention. (Choices B and D) Spinal cord injury or stroke can lead to urinary retention due to motor nerve injury (neurogenic bladder) or due to spasm of the internal urethral sphincter. This patient's acute-onset urinary retention following diphenhydramine ingestion makes anticholinergic-induced impairment of detrusor contraction more likely. Shingles (varicella-zoster virus reactivation) typically involves sensory nerves and motor nerve involvement would be unusual. (Choice E) Extrinsic compression of the urethra commonly occurs in older men due to BPH. Common symptoms include urinary urgency, difficulty with initiating and maintaining urinary stream, and feeling of incomplete bladder emptying. This patient likely has some component of BPH-related obstruction; however, he had not been having difficulty voiding until taking diphenhydramine. Educational objective: First-generation H1-antihistamines have potent anticholinergic effects and may cause eye and oropharyngeal dryness as well as urinary retention. Due to a high prevalence of benign prostatic hyperplasia, elderly men are at increased risk of urinary retention due to anticholinergic activity. References: Adverse effects of medications on urinary symptoms and flow rate: a community-based study. (http://www.ncbi.nlm.nih.gov/pubmed/8622001)

A 72-Year-Old Man Comes to the Emergency Department Due to a 24-Hour