A case report of lymphomatoid papulosis: uncovering a rare diagnosis from a common finger ulcer.

Lymphomatoid papulosis (LyP) is a rare, chronic CD30+ cutaneous lymphoproliferative disorder characterized by recurrent, self-healing papulonodular lesions. Despite its benign clinical course, LyP histologically resembles malignant lymphomas, necessitating careful differentiation. A 42-year-old woman presented with a 3-year history of recurring ulcerated papulonodular lesions on her index finger. Histopathological examination revealed atypical CD30+ lymphoid proliferation, confirming LyP type A. Immunohistochemical analysis was positive for CD2, CD4, CD30, and MUM-1, while systemic malignancy was excluded. The patient was treated with low-dose methotrexate (15 mg/week), leading to symptom improvement. LyP is classified into five histological subtypes (A-E) and is often misdiagnosed due to its overlap with inflammatory and neoplastic conditions. While the condition typically resolves spontaneously, it is associated with an increased risk of secondary lymphomas, including mycosis fungoides and primary cutaneous anaplastic large cell lymphoma. Accurate diagnosis relies on clinical presentation, histopathological evaluation, and immunophenotyping. Awareness of LyP's clinical and pathological features is essential for appropriate management and surveillance.