The spectrum of pigmented purpuric dermatosis and mycosis fungoides: atypical T-cell dyscrasia.

We report the case of a healthy 17-year-old adolescent boy with an unremarkable medical history who presented with an asymptomatic fixed rash on the abdomen, buttocks, and legs. The rash initially developed in a small area on the right leg 2 years prior and had progressed slowly. Prior biopsies were consistent with pigmented purpura. Clinical examination revealed multiple annular purpuric patches on the abdomen, buttocks, and legs covering approximately 20% of the body surface area without lymphadenopathy or hepatosplenomegaly. Additional biopsies demonstrated changes consistent with mycosis fungoides (MF). T-cell receptor g gene rearrangements demonstrated clonality. The patient was diagnosed with stage IB MF of the pigmented purpura-like variant. The patient responded well to psoralen plus UVA therapy. It has been proposed that pigmented purpuric dermatosis (PPD) is a form of cutaneous T-cell lymphoid dyscrasia and that T-cell gene rearrangement studies should be obtained for prognostic evaluation in patients with widespread disease. In our patient, the clinical appearance of the lesions, pathologic findings, and gene rearrangement studies led to the diagnosis of MF. Until the potential for evolution of PPD to malignant disease is better understood, further evaluation of MF in patients with an unusual presentation of pigmented purpura is warranted.