How to differentiate between Benign Prostatic Hyperplasia (BPH) and Overactive Bladder (OAB) in an older adult male patient presenting with urinary symptoms?

Distinguishing Between BPH and Overactive Bladder

The key distinction is that OAB is defined by urgency as the hallmark symptom—a sudden, compelling desire to void that is difficult to defer—while BPH primarily presents with voiding symptoms (weak stream, hesitancy, intermittency, incomplete emptying) though it can secondarily cause storage symptoms through bladder outlet obstruction. 1, 2

Core Diagnostic Features

Overactive Bladder Characteristics

• Urgency is mandatory for diagnosis: The sudden, compelling desire to pass urine which is difficult to defer must be present and bothersome 1
• Storage symptoms predominate: Frequency (>7 voids during waking hours), nocturia with small-volume voids, and urgency incontinence 1
• No obstruction required: OAB can occur without any anatomic obstruction or prostate enlargement 1
• Volume pattern: Nocturia in OAB typically involves small-volume voids, unlike the normal or large-volume voids seen in nocturnal polyuria 1

BPH Characteristics

• Voiding symptoms are primary: Weak urinary stream, intermittency, hesitancy, straining, and sensation of incomplete emptying 2, 1
• Prostate enlargement on exam: Digital rectal examination reveals enlarged prostate 1, 2
• Storage symptoms are secondary: When present, urgency and frequency develop as a consequence of bladder outlet obstruction causing detrusor overactivity 3, 4
• Age-related prevalence: Symptoms typically begin after age 40, affecting 60% by age 60 and 80% by age 80 2

Essential Diagnostic Workup

Mandatory Initial Assessment

• History focusing on symptom type: Specifically distinguish between storage symptoms (urgency, frequency, nocturia) versus voiding symptoms (weak stream, hesitancy, straining) 1
• Digital rectal examination: Assess prostate size and exclude nodules; enlarged prostate suggests BPH rather than isolated OAB 1
• Urinalysis: Rule out urinary tract infection and hematuria in both conditions 1

Additional Discriminating Tests

• Post-void residual (PVR): Elevated PVR (>250-300 mL) suggests bladder outlet obstruction from BPH rather than OAB 1, 3
• Frequency-volume chart: Particularly useful when nocturia predominates; small-volume frequent voids suggest OAB, while normal/large volumes suggest other causes 1, 2
• Symptom questionnaires: AUA-SI or IPSS scores help quantify BPH severity (mild 0-7, moderate 8-19, severe 20-35) 2
• PSA measurement: When life expectancy >10 years, helps assess prostate size and exclude malignancy in suspected BPH 1

Critical Distinguishing Algorithm

Step 1: Identify Predominant Symptom Pattern

• If urgency is the dominant, bothersome symptom with frequency and nocturia → Consider OAB as primary diagnosis 1
• If weak stream, hesitancy, and incomplete emptying predominate → Consider BPH as primary diagnosis 2, 1

Step 2: Assess for Obstruction

• Perform DRE: Enlarged prostate points toward BPH 1
• Measure PVR: Elevated residual (>250 mL) indicates obstruction consistent with BPH 1, 3
• Check uroflowmetry if available: Reduced maximum flow rate (<10 mL/sec) suggests BPH-related obstruction 5

Step 3: Recognize Overlap Scenarios

• BPH can cause secondary OAB symptoms: Bladder outlet obstruction from BPH induces detrusor overactivity, producing urgency and frequency 3, 4
• Both conditions commonly coexist: Older men may have both anatomic BPH and primary OAB 6
• Treatment response helps clarify: Alpha-blockers improve BPH voiding symptoms; antimuscarinics target OAB urgency 6, 7

Common Pitfalls to Avoid

Misattribution of Symptoms

• Do not assume all LUTS in older men are BPH: Isolated urgency without voiding symptoms or prostate enlargement is OAB, not BPH 1, 8
• Do not overlook detrusor underactivity: Chronic BPH can cause impaired bladder contractility, mimicking or complicating the clinical picture 3
• Do not ignore nocturia volume patterns: Large-volume nocturnal voids suggest nocturnal polyuria (cardiac, sleep apnea, diabetes) rather than OAB or BPH 1

Diagnostic Oversights

• Do not skip DRE in men with LUTS: Failure to assess prostate size misses the key physical finding distinguishing BPH from OAB 1
• Do not attribute hematuria solely to BPH: Always exclude bladder stones, bladder cancer, or upper tract pathology 3
• Do not use urodynamics or cystoscopy initially: These are not indicated for uncomplicated presentations of either condition 1

Treatment Implications

• Recognize that treating BPH may not resolve OAB symptoms: Storage symptoms often persist despite alpha-blocker therapy if primary OAB coexists 6
• Consider combination therapy when both present: Alpha-blockers plus antimuscarinics address both BPH obstruction and OAB urgency 5, 6
• Monitor for urinary retention with antimuscarinics: Use caution when PVR is 250-300 mL or higher, as antimuscarinics can worsen retention in obstructed patients 1