Primary Cutaneous CD4+ Small or Medium T-cell Lymphoproliferative Disorder Disguised as a B-cell Lymphoma

Summary: A 65-year-old female presented with erythematous eyelid papules and a pink pruritic plaque on her arm. The eyelid biopsy revealed dense dermal nodular infiltrate of CD20+ B-cells surrounding a population of pleomorphic small to medium T-cells, admixed with few (<30%) larger cells. Lymphoid cells showed nuclear irregularity, mostly scant cytoplasm, with rare mitoses. The infiltrate spared the epidermis. Given the clinical presentation of papules on the head and neck, a B-cell neoplasm was considered. However, unusual features of focal adnexotropism were present with follicular destruction. Additionally, PD-1 positive CD4 helper T-cells comprised a majority of the T cell infiltrate. The biopsy was investigated with molecular testing and a positive T-cell receptor gene rearrangement identified. The findings were interpreted as most consistent with CD4-positive small/medium T-cell lymphoproliferative disorder, a relatively new entity in the 2016 WHO classification, with excellent prognosis. The patient underwent treatment with methotrexate and localized radiation to eyelid lesions. This case highlights the pitfall of CD4 small/medium T-cell lymphoproliferative disorder with robust reactive B-cell component simulating B-cell lymphoma. We have encountered this phenomenon in a separate patient with a similar presentation. Recognizing the distinction of these diagnoses is paramount, as targeted agents e.g. rituximab would likely be inappropriate.