What is the differential diagnosis for an elderly black man with three round brownish discolorations (about 8 mm in diameter) on the inside of his bottom lip that have been present for approximately four days?

Differential Diagnosis for Brownish Discolorations on the Lower Lip

The most likely diagnoses for three round, 8mm brownish discolorations on the lower lip present for four days in an elderly Black man are oral melanoacanthoma (most likely given the acute 4-day onset), melanotic macules, or physiologic racial pigmentation, with oral melanoma being a critical but less likely consideration that must be excluded through biopsy.

Primary Differential Considerations

Oral Melanoacanthoma (Most Likely)

• Oral melanoacanthoma is a rare, benign, reactive pigmented lesion characterized by rapid onset, which aligns with the 4-day presentation described 1, 2
• The lesions typically appear as brown-to-black macules or patches, commonly affecting the buccal mucosa, lip, and palate 1, 2
• The average age of presentation is 28-38 years, with a strong female predilection (2.6:1) and predominance in Black patients 1, 2
• The clinical behavior suggests a reactive origin, and lesions are characteristically asymptomatic 2
• Duration ranges from one week to twelve months in reported cases, making the 4-day timeline consistent with this diagnosis 2

Melanotic Macules

• Oral melanotic macules are small, well-circumscribed brown-to-black macules occurring on lips and mucous membranes 1, 3
• The average age of presentation is 43 years with female predilection, and they may represent a physiologic or reactive process 1
• These lesions are typically smaller (often <1cm) and more chronic in nature, making the acute 4-day onset somewhat atypical 4

Physiologic Racial Pigmentation

• Racial pigmentation is common in Black individuals and can present as multifocal brown macules 3
• However, the acute 4-day onset makes this diagnosis less likely, as physiologic pigmentation typically develops gradually over time 3

Critical Exclusion: Oral Melanoma

Warning Signs Requiring Immediate Attention

• While less common on mucosal surfaces, oral melanoma must be excluded through biopsy, as it carries significant mortality risk if not diagnosed early 5, 6
• Key melanoma warning signs include: asymmetry, irregular borders, heterogeneous color, diameter >5-7mm, and dynamics (evolution/recent change) 5
• The 8mm diameter and 4-day evolution warrant careful evaluation, though the multiple symmetric lesions make melanoma less likely 5
• Progressive change in lesion size is a major sign requiring excision 6

Additional Differential Considerations

• Peutz-Jeghers syndrome should be considered if multiple pigmented macules are present on the lips, particularly if accompanied by gastrointestinal symptoms or family history 7
• Drug-induced pigmentation, foreign body pigmentation, and blue nevus are additional considerations in the differential 3

Diagnostic Approach

Mandatory Next Steps

• A full excisional biopsy with 2mm margin of normal skin is the standard practice for suspected malignant melanocytic lesions, not partial biopsy 5, 6
• Use a surgical knife rather than laser or electrocoagulation to avoid tissue destruction that may interfere with diagnosis 5, 6
• Histopathologic examination is mandatory to distinguish between benign pigmented lesions (melanoacanthoma, melanotic macule) and malignant melanoma 4, 1, 3

Clinical Examination Requirements

• Complete physical examination including the entire skin surface and all regional lymph nodes (preauricular and cervical) is necessary 6
• Document the exact size, color heterogeneity, border characteristics, and any signs of ulceration, bleeding, or inflammation 5
• Obtain detailed history regarding duration, rate of change, symptoms (itching, bleeding), medication use, and family history 3

Common Pitfalls to Avoid

• Do not assume benign diagnosis based on clinical appearance alone—benign pigmented lesions can be mistaken for malignant tumors when they exhibit similar coloration, symmetry, and borders 4
• Do not delay biopsy in elderly patients with new pigmented lesions, as melanoma incidence peaks at 65 years 5
• The acute 4-day onset strongly favors melanoacanthoma over melanoma, but histologic confirmation remains essential 2
• Clinicians are often unaware of melanoacanthoma, leading to unnecessary patient anxiety about melanoma 2