How do you differentiate between overactive bladder (OAB) and benign prostatic hyperplasia (BPH) in an older adult male patient presenting with urinary symptoms?

Differentiating Overactive Bladder from Benign Prostatic Hyperplasia

The key distinction is that OAB is characterized by sudden, compelling urgency that is difficult to defer as the hallmark symptom, while BPH primarily presents with voiding symptoms (weak stream, hesitancy, straining) alongside storage symptoms, and requires digital rectal examination showing prostatic enlargement. 1

Clinical Symptom Patterns

Overactive Bladder Presentation

• Urgency is the defining feature - a sudden, compelling desire to void that is difficult to defer, which must be present for OAB diagnosis 1
• Storage symptoms predominate: frequency (>7 voids during waking hours), nocturia with small-volume voids, and urgency incontinence 1
• Voiding symptoms are absent - no hesitancy, weak stream, or straining 1
• Symptoms occur in the absence of prostatic enlargement on examination 1

BPH Presentation

• Mixed symptom pattern with both voiding and storage components 1
• Voiding symptoms are prominent: weak stream, hesitancy, intermittency, straining, sensation of incomplete emptying 1, 2
• Storage symptoms (urgency, frequency, nocturia) are secondary to bladder outlet obstruction 1, 3
• Digital rectal examination reveals prostatic enlargement 2

Essential Diagnostic Steps

History Taking

• Document the presence and severity of urgency - if urgency is the predominant, bothersome symptom without voiding complaints, suspect OAB 1
• Assess voiding pattern - hesitancy, weak stream, and straining point toward BPH 1, 2
• Review medications that could cause symptoms (anticholinergics, alpha-agonists) 1
• Evaluate for neurologic conditions that affect bladder function 1

Physical Examination

• Digital rectal examination is mandatory to assess prostate size, consistency, and exclude nodules 2, 1
• Enlarged prostate on DRE strongly suggests BPH as the primary etiology 2
• Normal prostate size with predominant urgency indicates OAB 1
• Assess abdomen for bladder distention and lower extremities for edema 1

Objective Measurements

• Administer the International Prostate Symptom Score (IPSS) - quantifies symptom severity and distinguishes voiding from storage symptoms 1, 2
• Obtain a 3-day bladder diary - differentiates small-volume frequent voids (OAB) from normal/large-volume voids (nocturnal polyuria or BPH with overflow) 1, 2
• Measure post-void residual (PVR) - elevated PVR (>100 mL) indicates bladder outlet obstruction from BPH, while normal PVR suggests OAB 2, 3
• Perform uroflowmetry - maximum flow rate <10 mL/second indicates significant obstruction from BPH 3

Laboratory Testing

• Urinalysis to exclude infection and hematuria in both conditions 1
• PSA testing helps predict BPH progression risk and excludes prostate cancer 2
• Urine culture if urinalysis is abnormal 1

Algorithmic Approach to Differentiation

Step 1: Identify Predominant Symptom

• If urgency is the hallmark symptom with frequency and nocturia, but no voiding symptoms → suspect OAB 1
• If voiding symptoms (weak stream, hesitancy, straining) are present alongside storage symptoms → suspect BPH 1, 2

Step 2: Perform Digital Rectal Examination

• Enlarged prostate → BPH is the primary diagnosis 2, 1
• Normal-sized prostate with urgency → OAB is the diagnosis 1

Step 3: Measure Post-Void Residual

• Elevated PVR (>100 mL) → bladder outlet obstruction from BPH 2, 3
• Normal PVR (<50 mL) with urgency → OAB 1

Step 4: Review Bladder Diary

• Small-volume frequent voids throughout day and night → OAB 1
• Normal/large-volume nocturia with daytime frequency → consider BPH with secondary storage symptoms or nocturnal polyuria 1, 2

Critical Pitfalls to Avoid

• Do not assume all storage symptoms in older men are due to BPH - OAB can coexist or be the primary problem 4
• Do not diagnose BPH without performing digital rectal examination - prostate size assessment is essential 2
• Do not overlook the possibility of both conditions coexisting - approximately 44% of men with BPH have severe OAB symptoms requiring combination therapy 5
• Do not rely solely on symptom questionnaires - objective measures (PVR, uroflowmetry, DRE) are necessary to differentiate 2, 3
• Do not assume nocturia alone indicates OAB - it is multifactorial and can result from nocturnal polyuria, sleep disorders, or BPH 1

When Both Conditions Coexist

• If BPH is confirmed (enlarged prostate, elevated PVR) but storage symptoms persist despite alpha-blocker therapy, consider adding antimuscarinic therapy for concurrent OAB 4, 5
• Combination therapy with alpha-blockers and antimuscarinics is safe and effective for men with BPH and severe OAB symptoms 4, 5