What are the causes and treatments of brown spots on the penis?

Brown Spots on the Penis: Causes and Management

Brown spots on the penis require immediate biopsy if they are pigmented, indurated, fixed, or ulcerated, as melanoma of the penis, though rare, carries a very poor prognosis and early diagnosis is paramount. 1, 2

Diagnostic Approach

Immediate Biopsy Indications

The British Association of Dermatologists mandates biopsy for:

• Any pigmented areas to exclude abnormal melanocytic proliferation 1
• Lesions that are indurated, fixed, or ulcerated 3
• Persistent areas of hyperkeratosis, erosion, or erythema 1
• New warty or papular lesions 1
• Disease failing to respond to adequate treatment 1

Dermoscopy should be used systematically for all pigmented penile lesions, as it can reveal characteristic patterns such as prominent, wide, irregular pigment networks that suggest melanoma in situ. 2

Key Differential Diagnoses for Brown/Pigmented Penile Lesions

1. Melanoma (Most Critical)

• Presents as asymptomatic brown macules or patches 2
• Melanoma in situ of the penis is extremely rare but has very poor prognosis if not caught early 2
• Requires urgent referral to specialist urologist for excision and staging 1

2. Bowen's Disease of the Penis (Penile Intraepithelial Neoplasia)

• Appears as red, sometimes slightly pigmented, scaly patches and plaques on keratinized penis 1
• Has malignant transformation potential to squamous cell carcinoma 1
• Risk factors include lack of circumcision, HPV infection, and lichen sclerosus 1
• Early biopsy is clearly indicated before treatment 1

3. Bowenoid Papulosis

• Occurs in younger, sexually active men 1
• Presents as raised papules on glans, shaft, prepuce, and groin 1
• Associated with HPV exposure and has full-thickness dysplasia histologically 1
• Must be distinguished from benign pearly penile papules, which are normal anatomical variants requiring only reassurance 4

4. Lichen Sclerosus with Pigmentation

• Typically presents as porcelain-white plaques but may have pigmented areas 1
• Requires biopsy to exclude abnormal melanocytic proliferation 1
• Associated with increased risk of squamous cell carcinoma, requiring long-term follow-up 1
• Affects prepuce, coronal sulcus, and glans penis 1

5. Seborrheic Keratoses

• Can present as skin-colored papules and verrucoid plaques 5
• Clinically may resemble condyloma acuminatum 5
• Benign but requires histologic evaluation to confirm diagnosis 5

6. Normal Variants

• Penile hyperpigmentation is a normal variant, particularly in darker-skinned individuals 6
• Removal only appropriate for cosmetic purposes 6
• Requires clinical distinction from pathologic lesions 6

Common Pitfalls to Avoid

Critical Errors

• Never confuse pigmented lesions with genital warts and treat with cryotherapy, podophyllin, or imiquimod without biopsy 1, 4
• Do not assume brown spots are benign without proper evaluation, as melanoma can present as asymptomatic brown macules 2
• Avoid dismissing pigmented areas in lichen sclerosus patients without biopsy, as these require exclusion of melanocytic proliferation 1

Diagnostic Confusion

• Bowenoid papulosis can be confused with pearly penile papules, but the former has malignant potential while the latter is entirely benign 4
• Seborrheic keratoses may clinically mimic condyloma acuminatum, requiring histologic differentiation 5

Management Algorithm

Step 1: Clinical Examination

Document the following characteristics:

• Diameter, location, number of lesions 1
• Morphology: papillary, nodular, ulcerous, or flat 1
• Color: brown, pigmented, erythematous, or white 1
• Texture: indurated, fixed, scaly, or verrucoid 1, 3

Step 2: Risk Stratification

High-risk features requiring urgent biopsy and specialist referral:

• Any pigmented lesion with irregular borders or changing appearance 2
• Ulceration, induration, or fixation 3
• Persistent hyperkeratosis or erosion 1
• Failure to respond to treatment 1

Step 3: Biopsy Technique

• Punch, excisional, or incisional biopsy for histologic diagnosis 1
• For suspected melanoma, ensure adequate sampling 2
• Multiple mapping biopsies may be required if extensive abnormality present 1

Step 4: Specialist Referral

• Urgent referral to specialist urologist for lesions highly suspicious of squamous cell carcinoma or melanoma 1
• Multidisciplinary approach with dermatologist and urologist for complex cases 1