What are the causes and treatments of purple bumps on the shaft of the penis and scrotum?

Purple Bumps on Penis and Scrotum: Diagnosis and Management

The most likely diagnosis for purple bumps on the penile shaft and scrotum in an otherwise asymptomatic patient is angiokeratoma, a benign vascular lesion requiring no treatment unless symptomatic or cosmetically concerning, though urgent evaluation is mandatory to exclude life-threatening necrotizing infection (Fournier gangrene) if systemic symptoms are present.

Immediate Risk Stratification

First, assess for signs of necrotizing infection requiring emergency surgical intervention:

• Systemic toxicity (fever, tachycardia, diaphoresis) indicates possible Fournier gangrene, which requires immediate surgical debridement and broad-spectrum antibiotics 1
• Pain, erythema, swelling, or skin necrosis progressing over 1-2 days suggests necrotizing soft tissue infection 1
• Crepitus or gas in tissue on palpation or imaging is universally present in advanced Fournier gangrene 1
• Fournier gangrene has mean age of onset at 50-60 years and 80% have underlying diabetes mellitus 1

If any concerning features are present, obtain immediate surgical consultation before completing diagnostic workup.

Benign Vascular Lesions (Most Common)

For asymptomatic purple bumps without systemic symptoms, angiokeratoma is the primary consideration:

• Present as dome-shaped papules 0.5-5 mm in size, appearing red, purple, blue, or black along the penile coronal rim and scrotum 2
• Represent ectatic blood vessels in the papillary dermis with overlying acanthosis and hyperkeratosis 2
• Typically occur as idiopathic scrotal tumors (Fordyce angiokeratoma), with rare penile involvement 2, 3
• May present with spontaneous bleeding from individual papules 3
• Biopsy is indicated to exclude melanoma if diagnosis is uncertain, showing dilated thin-walled vascular structures in upper dermis 2
• No treatment required unless symptomatic or cosmetically concerning; laser surgery is an option for multiple coalescing lesions 2

Critical exclusions for angiokeratoma:

• Rule out angiokeratoma corporis diffusum (Fabry syndrome) by excluding intra-abdominal masses, urinary tract tumors, varicoceles, and hernias 3
• Exclude malignant melanoma (nodular type) through biopsy if lesions are atypical 3

Inflammatory/Vasculitic Causes

Henoch-Schönlein purpura can present with purpuric lesions on glans, shaft, and scrotum:

• Typically occurs in children ages 4-7 years but can affect adults 4
• Associated with palpable purpura, glomerulonephritis, arthralgias, and gastrointestinal symptoms 4
• Requires evaluation for renal involvement, which can be progressive and fatal 4

Traumatic purpuric ulcers:

• May result from mechanical trauma (friction during sexual activity or masturbation) 5
• Present as irregularly shaped shallow ulcers over purpuric base 5
• Heal spontaneously within 2 weeks with topical therapy 5

Infectious Causes Requiring Treatment

If sexually active male under 35 years with associated symptoms:

• Gonococcal and chlamydial infections are most common infectious causes, often presenting with urethritis and penile edema 6
• Obtain urethral swab or first-void urine for N. gonorrhoeae and C. trachomatis testing 7
• Treatment for chlamydial/gonococcal urethritis: Ceftriaxone 250 mg IM single dose plus doxycycline 100 mg orally twice daily for 7-10 days 8, 9

For Fournier gangrene (if diagnosed):

• Immediate aggressive surgical debridement to remove all necrotic tissue 1
• Empirical antibiotics: Vancomycin plus coverage for enteric gram-negative bacilli and anaerobes 1
• Mixed aerobic and anaerobic flora including Staphylococcus aureus and Pseudomonas species 1

Diagnostic Algorithm

Step 1: Assess for systemic symptoms (fever, tachycardia, pain, rapidly progressing erythema/necrosis)

• If present → Emergency surgical consultation for possible Fournier gangrene 1

Step 2: If asymptomatic purple bumps without systemic symptoms:

• Ultrasound with Doppler as first-line imaging to assess vascular structures and exclude complications 6
• Consider punch or excisional biopsy to confirm angiokeratoma and exclude melanoma 2

Step 3: If sexually active with associated urethral symptoms:

• Test for N. gonorrhoeae and C. trachomatis 7
• Treat empirically while awaiting results 8, 9

Step 4: If pediatric patient or systemic vasculitic symptoms:

• Evaluate for Henoch-Schönlein purpura with renal function assessment 4

Common Pitfalls

• Delaying surgical consultation when Fournier gangrene is suspected—mortality is high without immediate debridement 1
• Assuming all purple lesions are benign—biopsy is essential to exclude melanoma 2, 3
• Missing Fabry syndrome in patients with angiokeratoma—requires systemic evaluation 3
• Failing to test for STIs in sexually active patients with genital lesions 6, 7
• Not recognizing traumatic etiology—detailed sexual history may reveal mechanical cause 5