A 72-year-old man with benign prostatic hyperplasia is being counselled about the natural history and complications of his condition. Which of the following is the most common cause of acute urinary retention in men with BPH?

## Acute Urinary Retention in BPH **Key Point:** Acute urinary retention (AUR) in men with BPH is most commonly triggered by **sudden increase in bladder outlet resistance** from acute prostatic edema, congestion, or inflammation superimposed on chronic obstruction, rather than primary detrusor failure. ### Mechanisms of Acute Urinary Retention in BPH | Mechanism | Frequency | Pathophysiology | Clinical Context | |-----------|-----------|-----------------|------------------| | **Acute prostatic edema/congestion** | Most common | Sudden increase in outlet resistance; loss of compensatory detrusor contraction | Follows UTI, sexual activity, prolonged sitting, cold exposure, anticholinergic drugs | | Acute prostatitis | Common | Inflammatory edema + pain inhibition of voiding reflex | Dysuria, fever, perineal pain; bacterial or abacterial | | UTI-related decompensation | Common | Mucosal irritation + detrusor hyperactivity → decompensation | Dysuria, frequency, urgency preceding retention | | Detrusor failure | Less common | Loss of contractility from chronic high-pressure voiding | Late-stage disease; poor prognosis; may be irreversible | | Medications | Variable | Anticholinergics, sympathomimetics, opioids | Exacerbating factor, not primary cause | **High-Yield:** The distinction is critical: **acute retention is usually reversible** (outlet obstruction) whereas **chronic retention with elevated post-void residual may progress to detrusor failure** (irreversible). ### Clinical Presentation **Clinical Pearl:** A man with known BPH who suddenly cannot void after a UTI, sexual activity, or exposure to cold (causing vasoconstriction and prostatic congestion) is experiencing acute outlet obstruction, not primary bladder failure. This is why catheterization + antibiotics + α-blockers often restore spontaneous voiding. ### Risk Factors for AUR in BPH 1. **Acute infection** (UTI, prostatitis) 2. **Medications** (anticholinergics, decongestants, opioids) 3. **Behavioral triggers** (prolonged immobility, cold exposure, sexual activity) 4. **Bladder overdistension** (high fluid intake, delayed voiding) 5. **Acute inflammation** (from instrumentation, biopsy) **Mnemonic:** **ACUTE** — **A**cute infection, **C**ongestion/edema, **U**reteral/outlet obstruction, **T**riggers (medications, cold), **E**dema from inflammation. ### Why Detrusor Failure Is NOT the Most Common Cause Detrusor failure (chronic retention with elevated post-void residual progressing to overflow incontinence) is a **late-stage complication** of BPH, not the typical presentation of acute retention. Most men with AUR have reversible outlet obstruction and recover normal voiding after relief of the acute precipitant.