What is the differential diagnosis for acute onset swelling of the central part of the prepuce without dysuria or discharge?

Differential Diagnosis for Acute Onset Isolated Prepucial Swelling

The most likely diagnoses for acute onset swelling isolated to the central prepuce without dysuria or discharge are balanoposthitis (inflammation of the glans and foreskin), paraphimosis (retracted foreskin trapped behind the glans), or localized trauma/edema, with balanoposthitis being most common in the absence of a clear history of foreskin manipulation. 1

Primary Differential Considerations

Balanoposthitis (Most Common)

• Bacterial colonization and infection of the prepuce occurs in 4-11% of uncircumcised males and represents the most frequent inflammatory condition 1
• Presents with localized swelling, erythema, and tenderness of the prepuce without necessarily involving urethral symptoms 1
• Can occur without discharge in early stages or with minimal bacterial load 2
• The absence of dysuria helps distinguish this from urethritis-associated conditions 3

Paraphimosis (Surgical Emergency)

• Occurs when retracted foreskin becomes trapped behind the glans penis and cannot be returned to normal position 1
• Creates venous congestion leading to progressive swelling of the prepuce distal to the constriction ring 1
• Requires immediate manual reduction or dorsal slit incision if manipulation fails 1
• Critical pitfall: Delayed recognition beyond 6-8 hours significantly increases risk of tissue necrosis 4

Localized Trauma or Edema

• Isolated preputial injury can occur from direct trauma, even minor mechanisms 5
• Post-inflammatory edema from various causes including allergic reactions or contact dermatitis 6
• Lymphatic obstruction causing localized fluid accumulation without infection 6

Less Common but Important Considerations

Phimosis with Secondary Inflammation

• Pathologic phimosis (inability to retract foreskin due to fibrosis) can lead to trapped secretions and secondary swelling 1
• Distinguished from physiologic phimosis by presence of scarring or balanitis xerotica obliterans 1
• May present acutely if previously asymptomatic phimosis becomes inflamed 2

Early Fournier's Gangrene (Cannot Miss Diagnosis)

• Necrotizing soft tissue infection can present with insidious onset in up to 40% of cases, with initial localized penile/preputial swelling before systemic signs develop 7
• High-risk patients include diabetics, immunosuppressed individuals, and those with recent urogenital procedures 7, 8
• Requires immediate broad-spectrum antibiotics and surgical debridement once suspected 7
• Look for: fever, tachycardia, diaphoresis, crepitus, or skin discoloration beyond simple erythema 8

Sexually Transmitted Infection (STI)-Related

• In sexually active men under 35 years, consider gonococcal or chlamydial infection causing localized inflammation 8
• However, the absence of urethral discharge and dysuria makes classic STI-related urethritis less likely 3
• Epididymitis typically presents with testicular/epididymal tenderness, not isolated prepucial swelling 3

Diagnostic Approach Algorithm

Step 1: Immediate Assessment

• Attempt gentle manual retraction of foreskin to rule out paraphimosis 1
• Assess for systemic signs (fever >38.3°C, tachycardia, altered mental status) suggesting necrotizing infection 7
• Examine for skin changes: simple erythema vs. dusky discoloration, crepitus, or bullae 7

Step 2: Risk Stratification

• If diabetic, immunosuppressed, or recent urogenital procedure → consider Fournier's gangrene and obtain urgent imaging 7, 8
• If sexually active young male → consider STI evaluation despite atypical presentation 8
• If history of foreskin manipulation → paraphimosis more likely 1

Step 3: Imaging When Indicated

• Ultrasound with Doppler is first-line imaging to assess for abscess, fluid collections, or underlying testicular pathology 8, 4
• CT or MRI if Fournier's gangrene suspected to define extent of fascial involvement 7

Step 4: Laboratory Evaluation

• For suspected infection: complete blood count, inflammatory markers (CRP, procalcitonin) 7
• Check glucose and HbA1c to identify undiagnosed diabetes 7
• Urinalysis to assess for pyuria if urinary symptoms develop 3

Treatment Based on Diagnosis

For Balanoposthitis

• Warm soaks, gentle hygiene, topical antibiotics if bacterial etiology suspected 2
• Oral antibiotics if cellulitis extends beyond prepuce 2
• Reevaluate within 3 days; failure to improve requires reassessment for alternative diagnosis 3, 4

For Paraphimosis

• Immediate manual reduction: apply firm compression to glans for 5-10 minutes to reduce edema, then attempt to pull prepuce forward 1
• If unsuccessful, dorsal slit incision followed by circumcision 1
• Do not delay beyond 2-4 hours as tissue viability decreases rapidly 4

For Suspected Necrotizing Infection

• Immediate broad-spectrum antibiotics covering mixed aerobic/anaerobic flora including staphylococci and Pseudomonas 8
• Urgent surgical consultation for debridement 7
• Suprapubic catheter for urinary diversion 7

Critical Pitfalls to Avoid

• Never assume isolated prepucial swelling is benign without assessing for paraphimosis or early necrotizing infection 7, 1
• Do not attribute all genital swelling to STIs; the absence of discharge and dysuria makes urethritis unlikely 3
• In diabetic or immunosuppressed patients, maintain high suspicion for Fournier's gangrene even with minimal external findings 7, 8
• Failure to improve within 72 hours of conservative management mandates imaging and specialist consultation 4