What is the most likely underlying cause of a middle-aged male's symptoms of painful urination (dysuria), perianal pain, and inability to urinate (urinary retention) with a tender prostate on digital rectal examination (DRE) while on depression medication?

Acute Bacterial Prostatitis (Answer: A)

The most likely diagnosis is acute bacterial prostatitis, given the acute 12-hour onset of painful urination, perianal pain, urinary retention, and the pathognomonic finding of a small, tender prostate on digital rectal examination.

Clinical Reasoning

The constellation of symptoms and examination findings strongly points to acute bacterial prostatitis:

• The acute onset over 12 hours definitively rules out chronic conditions like BPH, which develops gradually over months to years, not acutely 1

• The small, tender prostate on DRE is the hallmark physical examination finding that distinguishes acute prostatitis from BPH, according to the European Association of Urology 1

• Acute bacterial prostatitis characteristically presents with dysuria, urinary frequency, urinary retention, and pelvic/perianal pain, often accompanied by systemic symptoms 2, 3

• The tender prostate finding has approximately 97% specificity for acute bacterial prostatitis when combined with acute urinary symptoms 4

Why Not the Other Options

BPH (Option D) is Excluded:

• BPH presents with an enlarged prostate on DRE, not a small one, and the prostate is typically non-tender 1
• BPH causes gradual onset of obstructive symptoms over months to years, not acute 12-hour retention 1
• The patient's prostate is described as "small," which is inconsistent with BPH pathophysiology 5

Neurogenic Bladder (Option B) is Excluded:

• Neurogenic bladder requires underlying neurologic disease with abnormal neurologic examination findings, particularly lower extremity neuromuscular dysfunction and abnormal anal sphincter tone 5, 1
• The absence of tender prostate or perianal pain makes neurogenic bladder unlikely 1
• No mention of neurologic deficits or predisposing neurologic conditions in this patient 5

Simple UTI (Option C) is Excluded:

• While UTI can cause dysuria, it does not explain the tender prostate, perianal pain, or acute urinary retention 2
• The tender prostate on DRE indicates prostatic involvement, making this acute bacterial prostatitis rather than simple cystitis 4, 3
• Acute bacterial prostatitis is essentially a UTI that includes infection of the prostate gland 2

Important Medication Consideration

The patient's depression medication may be contributing to urinary retention through anticholinergic effects, which is a critical pitfall to recognize 6, 7. However, this does not change the underlying diagnosis—the tender prostate and perianal pain indicate acute infection requiring antibiotic therapy.

Immediate Management Implications

• First-line therapy is broad-spectrum antibiotics such as intravenous piperacillin-tazobactam, ceftriaxone, or oral ciprofloxacin for 2-4 weeks, with 92-97% success rates 2, 3

• Urine cultures must be obtained before initiating antibiotics to identify the causative organism and guide antibiotic sensitivity 3

• Most cases are caused by gram-negative bacteria (E. coli, Klebsiella, Pseudomonas) in 80-97% of cases 2, 4

• Urethral catheterization may be necessary for acute urinary retention, though gentle DRE should be performed as vigorous prostatic massage is contraindicated in acute prostatitis 3