A 72-year-old man with BPH presents with acute urinary retention following a course of oral decongestants. After catheter drainage and resolution of retention, he is evaluated for long-term management. His prostate volume is estimated at 45 mL on DRE, and he wishes to avoid surgery. Which investigation is most appropriate to guide pharmacological therapy selection?

Explanation

## Prostate Volume Assessment for Medical Therapy in BPH **Key Point:** Transrectal ultrasound (TRUS) is the most appropriate investigation to accurately measure prostate volume, which is the primary determinant of pharmacological therapy choice in BPH (alpha-blockers vs. 5-alpha reductase inhibitors). ### Why Prostate Volume Matters in Medical Management **High-Yield:** Prostate volume guides drug selection: - **Small-moderate glands (<30–40 mL):** Alpha-blockers (tamsulosin, alfuzosin) are first-line — rapid symptom relief - **Large glands (>40 mL):** 5-alpha reductase inhibitors (finasteride, dutasteride) are preferred — reduce prostate volume and long-term progression - **Very large glands (>50 mL) + retention:** Combined therapy (alpha-blocker + 5-ARI) or consider surgery **Clinical Pearl:** DRE-estimated prostate size is notoriously inaccurate (±50% error). TRUS provides objective measurement (±5 mL accuracy) essential for treatment planning. ### Role of TRUS in BPH Management | Clinical Scenario | TRUS Indication | Why | |---|---|---| | **Medical therapy selection** | **Yes** | Volume determines alpha-blocker vs. 5-ARI choice | | **Surgical planning (TURP, laser)** | **Yes** | Predicts resection time, morbidity, TUR syndrome risk | | **Acute retention** | Consider | Assess for post-void residual, upper tract dilatation | | **Recurrent UTI** | Consider | Rule out stones, diverticula, residual urine | **Mnemonic: TRUS for TURP** — Use TRUS before planning any **T**ransurethral **R**esection of **P**rostate to measure volume and assess feasibility. ### Why Other Options Are Incorrect in This Context **Warning:** Serum creatinine (option A) is important for baseline renal assessment in BPH, but does NOT guide pharmacological choice. Urodynamics (option B) is reserved for equivocal cases or neurogenic bladder, not routine medical therapy selection. Urinalysis (option D) screens for infection/hematuria but does not inform drug selection. [cite:Campbell-Walsh Urology 12e Ch 104]