Cutaneous Extracavitary Primary Effusion Lymphoma: A Case Report and Review of Literature.

Primary effusion lymphoma (PEL) is a rare B-cell lymphoma that is most often seen in immunocompromised patients with human herpesvirus-8 (HHV-8) and Epstein-Barr virus (EBV) infections. PEL typically affects body cavities with occasional involvement of other organs (extracavitary PEL). We present an unusual case of primary cutaneous extracavitary PEL without body cavity effusions. A 56-year-old man with uncontrolled HIV (CD4 count 50, viral load 264 copies/mL) presented with a 2-month history of fever, cough, and progressive dyspnea. Physical examination revealed bilateral inner thigh erythema and induration. Laboratory evaluation showed an elevated EBV viral load. Imaging studies did not reveal body cavity effusions. Skin biopsy from the thigh demonstrated a deep dermal and subcutaneous infiltrate of large pleomorphic lymphoid cells. The atypical cells were CD45+, CD138+, CD3+, HHV8+, EBV in situ hybridization (ISH)+, CD20-, CD79a- and PAX5 negative. Our case highlights a rare primary cutaneous manifestation of extracavitary PEL. It is important for dermatopathologists to be aware of the histopathological features of extracavitary PEL and its unusual immunophenotype (CD138+, negative for B-cell markers with aberrant expression of T-cell markers), which could represent a potential diagnostic pitfall. HHV-8 and EBER ISH positivity is crucial for the diagnosis of cutaneous extracavitary PEL.