Pigmented Lesions and Cutaneous Lymphoma
Scope
This domain separates benign from malignant pigmented lesions using morphology and dermoscopy, and covers cutaneous T-cell and B-cell lymphomas, especially mycosis fungoides.
Core rules
- Melanoma subtypes: superficial spreading, nodular, lentigo maligna, acral lentiginous. Dermoscopy shows atypical network, irregular globules, blue-white veil, regression, and polymorphous vessels.
- Acral lesions: benign nevi show parallel furrow pattern; melanoma shows parallel ridge pattern.
- Spitz nevus, blue nevus, and dysplastic nevi require clinicopathologic correlation; "ugly duckling" sign outperforms ABCDE in surveillance.
- Mycosis fungoides: epidermotropic CD4+ T cells with cerebriform nuclei, Pautrier microabscesses, patch/plaque/tumor stages; Sézary syndrome is leukemic.
- CD30+ lymphoproliferative disorders include lymphomatoid papulosis and primary cutaneous anaplastic large-cell lymphoma.
- B-cell lymphoma: follicular center or marginal zone; think of Borrelia in endemic areas.
Worked example
A pigmented macule on the sole shows a parallel ridge pattern on dermoscopy. Reasoning: pigment tracking the eccrine ridges rather than the furrows indicates acral melanoma; a full-thickness excision biopsy for histology is required, not a shave.
Traps
Do not call every longitudinal nail band melanoma; racial pigmentation is common. A shave biopsy may under-stage melanoma. MF can mimic eczema for years, so biopsy persistent patches.