Tumoral Stage of Mycosis Fungoides, Misdiagnosed With Wells Syndrome and Langerhans Cell Histiocytosis Histologically: A Challenging Case and Review of the Literature.

backgroundMycosis fungoides (MF) is a type of cutaneous T-cell lymphoma (CTCL) with slow progression, usually presenting with patches and plaques. The infiltration of histiocytes and eosinophils in skin cancers can mask the underlying condition, posing a diagnostic challenge. While cases of MF associated with tissue eosinophilia or histiocytosis infiltration resembling Langerhans cell histiocytosis (LCH) have been reported, the simultaneous occurrence of both conditions in a single MF patient has not been documented. CASE: In this case report, we presented an elderly man with a known history of patch and plaque-stage MF who developed a large cutaneous tumor on his right mandibular margin. Multiple biopsies initially led to misdiagnoses, attributing the lesion to Well's syndrome and LCH due to the dense infiltration of eosinophils and histiocytes, respectively. However, the absence of a BRAF V600 mutation and lack of clinical correlation reduced the likelihood of these initial diagnoses. After repeated biopsies and a thorough evaluation by hematopathology and dermatopathology specialists, the findings were reassessed, leading to the consideration of tumoral MF with reactive eosinophil and histiocyte infiltrates. The patient was subsequently started on chemotherapy and phototherapy, which led to tumor regression after treatment initiation.

conclusionThis case highlights the importance of considering MF in patients presenting with tissue eosinophilia or Langerhans cell infiltration, even when initial biopsies lack definitive features.