Brown Macules in Palmoplantar Psoriasis
Brown macules on the palms and soles in palmoplantar psoriasis are not a characteristic feature of the disease itself; palmoplantar psoriasis typically presents with erythematous, scaly, hyperkeratotic plaques and fissures, not brown macules. 1, 2
Understanding the Clinical Presentation
The appearance of brown macules suggests an alternative or concurrent diagnosis rather than a typical manifestation of palmoplantar psoriasis:
Typical Palmoplantar Psoriasis Features
- Palmoplantar psoriasis characteristically presents with erythematous scaly and fissured hyperkeratotic plaques, thick scaly skin, or an overlapping of both pustular and hyperkeratotic lesions. 1, 2
- The disease causes functional disability through fissuring, tissue hardening, and hyperkeratosis that affects daily activities, but brown macules are not part of the classic presentation. 2
Potential Causes of Brown Macules in This Context
Post-inflammatory hyperpigmentation is the most likely explanation for brown macules in a patient with palmoplantar psoriasis:
- Chronic inflammation from psoriatic plaques can lead to residual hyperpigmentation after lesions resolve or during active disease, particularly in darker skin types.
- This represents melanin deposition following inflammatory injury rather than a primary feature of psoriasis itself.
Alternative diagnoses to consider:
- Medication-induced changes: Certain anticancer agents can cause palmar-plantar erythrodysesthesia syndrome (PPES) with hyperpigmentation. 3
- Concurrent dermatoses: The brown macules may represent a separate condition occurring alongside palmoplantar psoriasis.
- Tinea nigra: A superficial fungal infection causing brown-black macules on palms and soles.
- Melanocytic lesions: Including lentigines or melanocytic nevi that happen to be present in the same location.
Clinical Approach
Distinguish between active psoriatic lesions and hyperpigmented macules:
- Active psoriatic plaques show scale, erythema, and often fissuring. 2
- Post-inflammatory hyperpigmentation appears as flat brown macules without scale or elevation.
- Perform dermoscopy or consider biopsy if the diagnosis remains uncertain.
Treatment implications:
- If the brown macules represent post-inflammatory hyperpigmentation from psoriasis, treating the underlying psoriatic inflammation is the primary approach. 4
- PUVA therapy (psoralen-ultraviolet A) should be considered for palmoplantar psoriasis treatment, though it may theoretically worsen hyperpigmentation in some cases. 4
- Oral PUVA should usually be considered as first-line PUVA treatment for palmoplantar dermatoses. 4
Critical Caveat
The presence of brown macules as a primary or prominent feature should prompt reconsideration of the diagnosis. If these macules are the dominant finding rather than typical psoriatic plaques, alternative diagnoses must be excluded through appropriate testing including potassium hydroxide (KOH) preparation, fungal culture, or skin biopsy.