P053 Mycosis fungoides in skin of colour: diagnostic lessons from a refractory case

Abstract

A 55-year-old man of Pakistani origin, currently residing in Ireland, presented with a 10-year history of a progressive scaly rash that began bilaterally on his hands and extended over 5 years to involve his arms, face and trunk. There was no history of inflamma­tory dermatoses, photosensitivity, fevers, night sweats or unintentional weight loss. Clinical examination revealed widespread hyperpigmented, scaly patches, some with atrophic change, and plaques affecting 53% of his body surface area. Over a 5-year period, three skin biopsies from different active sites demonstrated features suggestive of cutaneous lupus erythematosus. During this time, the patient was treated sequentially with hydroxychloroquine, methotrexate and mycophenolate mofetil without clinical improvement. The combination of treatment refractoriness and clinicopathological discordance prompted reconsideration of the diagnosis. Two deep 5-mm punch biopsies were subsequently obtained from representative lesions and sent for haematoxylin and eosin staining and T-cell receptor gene re­­arrangement studies. Histology demonstrated a dermal lymphoid infiltrate with epidermotropism and lymphoid nuclear atypia, while molecular analysis confirmed T-cell clonality with a CD8+ phenotype, establishing the diagnosis of mycosis fungoides (MF). MF is the most common subtype of cutaneous T-cell lymphoma and a recognized clinicopathological mimic of chronic inflammatory dermatoses. This case highlights several diagnostic pearls: the importance of maintaining a high index of suspicion in refractory disease; the need for repeated, adequately deep, multisite biopsies; and the value of clonality studies in strengthening the diagnosis. Cessation of topical corticosteroids for ≥ 2 weeks prior to biopsy is also recommended to optimize histological yield. The hyperpigmented phenotype observed aligns with a recognized MF variant more commonly reported in patients with skin of colour and is frequently associated with a CD8+ immunophenotype, strengthening clinicopathological correlation. This case underscores the importance of diagnostic persistence, optimized biopsy strategies and careful clinicopathological integration to avoid delayed diagnosis.