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Case Reports

Abstract

Mycosis fungoides (MF) is the most common primary form of cutaneous lymphoma and accounts for almost 50% of all these types of lymphoma. MF can mimic a diverse range of dermatoses, including psoriasis. MF patients are commonly misdiagnosed with psoriasis, or psoriasis preceding the diagnosis of MF. In addition, other cases of MF have presented with psoriasiform plaques clinically but histopathologically show MF features. We describe a case of a 49-year-old male who initially presented with plaque MF, was treated with skin radiation therapy with improvement. Following 2 years, the patient developed new eruptions, diagnosed as psoriasis with psoriatic arthritis, confirmed by pathology with no evidence of lymphoproliferative disorder. The patient was treated with disease-modifying antirheumatic drugs (DMARDs), both his skin lesions and arthritis improved. In his recent follow-up biopsy of a new lesion, the sections revealed large, atypical lymphocytes in single unit and small collections in the epidermis and superficial dermis, features of MF, diagnosis confirmed by immunohistochemical and T-cell gene rearrangement studies. The section also revealed mounds of parakeratosis containing neutrophils, spongiform pustules, psoriasiform epidermal hyperplasia and tortured blood vessels in the papillary dermis, features of psoriasis. The diagnosis features of both MF and classic psoriasis present in the same specimen. Unlike previous reported cases, our case exhibited an unusual presentation of psoriasis developing and superimposing a pre-existing MF, two separate entities in one lesion. This could be the consequence of both diseases share a common pathogenetic mechanisms associated with the abnormal activation of T-cells.