Overlapping Hyperpigmented and Poikilodermatous Mycosis Fungoides

Primary cutaneous T-cell lymphomas (pCTCLs) are a heterogeneous group of rare clonal T-cell disorders, among which mycosis fungoides (MF) is the most common subtype. Several clinicopathologic variants of MF have been described, including poikilodermatous and hyperpigmented forms, with occasional overlap between variants. We report a 68-year old man with a 25-year history of slowly progressive, asymptomatic dark plaques involving the lower extremities and intergluteal fold consistent with overlapping hyperpigmented and poikilodermatous MF. Unlike the classically reticulated appearance of poikilodermatous MF, the lesions displayed extensive, sharply demarcated confluent hyperpigmentation. 18F-FDG PET/CT demonstrated no systemic involvement, although the cutaneous lesions displayed mild hypermetabolism. Histopathological examination revealed epidermotropic atypical lymphocytes with superficial dermal lymphohistiocytic infiltrates, vascular ectasia, erythrocyte extravasation, hemosiderin deposition, and dermal melanophages. Immunophenotypic studies supported the diagnosis of MF with monoclonal T-cell receptor rearrangement. Disease staging was T2N0M0B0 (Stage IB). Given the longstanding indolent course, absence of symptoms, and lack of extracutaneous disease, a watch-and-wait strategy was adopted. Although hyperpigmentation may be observed in poikilodermatous MF, the unusually marked and confluent pigmentation in our patient exceeded the degree typically associated with poikiloderma alone, suggesting overlap with the hyperpigmented variant of MF. This case highlights the importance of careful clinicopathologic correlation in atypical pigmentary presentations of MF.