What is the differential diagnosis for brown macules on the palms?

Differential Diagnosis of Brownish Macules on Palms

The differential diagnosis for brown macules on the palms includes Peutz-Jeghers syndrome, acral lentiginous melanoma, drug-induced hyperpigmentation (particularly from chemotherapy or PUVA therapy), volar melanotic macules, Addison's disease, and acral lentigines—with the priority being to exclude melanoma and systemic syndromes that impact mortality.

Key Diagnostic Considerations

Life-Threatening/High-Mortality Conditions to Exclude First

Acral Lentiginous Melanoma

• Occurs on palms, soles, and subungual sites 1
• More common in darker-skinned individuals and represents a distinct clinical subtype with lower BRAF mutation rates (21%) compared to non-chronic sun damage melanomas 1
• Look for asymmetry, irregular borders, color heterogeneity, diameter >7mm, and recent evolution (ABCDE criteria) 2
• Critical pitfall: Acral melanomas are often diagnosed late due to lower clinical suspicion in these locations
• Requires excisional biopsy with 2mm margins for definitive diagnosis 2

Peutz-Jeghers Syndrome (PJS)

• Dark brown or blue-brown macules 1-5mm in size on lips (94%), buccal mucosa (66%), hands (74%), and feet (62%) 3
• Key distinguishing features: Buccal mucosa involvement (never seen in simple freckles), periorbital and perianal pigmentation 3
• Associated with hamartomatous gastrointestinal polyps and significantly increased cancer risk (gastrointestinal, breast, gynecologic)
• Autosomal dominant with STK11/LKB1 gene mutation 3
• Mortality impact: Requires lifelong cancer surveillance due to elevated malignancy risk

Drug-Induced and Iatrogenic Causes

Chemotherapy-Induced Hyperpigmentation

• Multiple agents cause palmoplantar pigmentation including 5-fluorouracil, capecitabine, doxorubicin, and targeted therapies 4
• Hand-foot syndrome (palmar-plantar erythrodysesthesia) can present with brownish discoloration before progressing to erythema and desquamation 4
• History of recent chemotherapy is diagnostic

PUVA-Induced Pigmented Macules

• Can occur after 12+ months of PUVA therapy, including localized palmoplantar treatment 5
• Histology shows pigmentary incontinence without cytologic atypia 5
• Important to distinguish from PUVA-associated malignancies (squamous cell carcinoma, melanoma) 6

Benign Conditions

Volar Melanotic Macules

• Asymptomatic light brown or tan-gray macules on palms/soles, more common in Black patients 7
• Purely epidermal hyperpigmentation without increased melanocyte number 7
• Benign but must be distinguished from secondary syphilis or post-inflammatory changes

Isolated Palmoplantar Lentiginosis

• Rare presentation of lentigo simplex limited to palms and soles 8
• Benign with no associated systemic conditions 8
• Diagnosis of exclusion after ruling out syndromic causes

Acral Lentigines

• May be associated with immunosuppression or lymphoproliferative disorders 9
• Biopsy shows basal cell layer pigmentation with increased melanocytes 9

Systemic Conditions

Addison's Disease

• Generalized hyperpigmentation including palmar creases
• Associated with fatigue, weight loss, hypotension, electrolyte abnormalities
• Check morning cortisol and ACTH levels

Diagnostic Algorithm

1. Immediate assessment for melanoma features: Any lesion with ABCDE criteria or recent change requires excisional biopsy 2

2. Check for mucosal involvement: Examine buccal mucosa, lips, and perioral areas

   • If present → Consider PJS, obtain family history, refer for GI evaluation 3
   • If absent → Proceed to step 3

3. Obtain medication/treatment history:

   • Recent chemotherapy → Likely drug-induced 4
   • History of PUVA therapy → Consider PUVA-induced macules 5
   • Immunosuppression → Consider acral lentigines 9

4. Assess for systemic symptoms:

   • Fatigue, weight loss, hypotension → Check cortisol/ACTH for Addison's
   • Lymphadenopathy, constitutional symptoms → Consider paraneoplastic process 9

5. If no concerning features and symmetric distribution: Likely benign volar melanotic macules 7 or isolated lentiginosis 8

Critical Pitfalls to Avoid

• Never assume palmar macules are benign without excluding melanoma, especially in patients with darker skin tones where acral melanoma is proportionally more common 1, 10
• Do not miss PJS: Failure to identify this syndrome delays cancer surveillance and increases mortality 3
• Biopsy technique matters: Use excisional biopsy with 2mm margins, not punch biopsy, to avoid missing melanoma diagnosis 2
• Consider drug history: Many oncologic agents cause palmoplantar pigmentation that can be confused with other conditions 4