15PPrimary skeletal muscle peripheral T-cell lymphoma associated with HIV presenting with myopathic symptoms

Primary skeletal muscle lymphoma (PSML) is a rare form of non-Hodgkin lymphoma (NHL), predominantly of B-cell lineage. T-cell variants are exceedingly uncommon, with fewer than ten reported cases of primary skeletal muscle peripheral T-cell lymphoma, not otherwise specified (PSM-PTCL, NOS). We present a case of HIV-associated PSM-PTCL, NOS with clinical features mimicking inflammatory myopathy. A 44-year-old man with a 5-year history of HIV presented with a 2-month history of intermittent fever and progressive limb weakness. Physical examination showed proximal-dominant muscle weakness and generalized edema. Laboratory tests revealed leukocytosis, anemia, elevated creatine kinase, metabolic acidosis, and negative myositis-specific autoantibodies. Electromyography showed a myopathic pattern. Due to rapidly worsening symptoms and lack of autoimmune markers, a muscle biopsy was performed. Histopathology showed diffuse infiltration of atypical lymphoid cells between muscle fibers. Immunohistochemistry revealed strong CD3 positivity and CD20 negativity, with high Ki-67 proliferation index (∼90%). Tumor cells were negative for CD10, CD117, CD34, CD68, CD99, pan-CK, MyoD1, MPO, TDT, and desmin, ruling out myogenic, myeloid, and epithelial malignancies. PET/CT revealed diffuse FDG uptake across multiple skeletal muscles with only minimal lymph node involvement. Bone marrow examination showed no infiltration. These findings confirmed the diagnosis of PSM-PTCL, NOS. Despite initiation of corticosteroids and chemotherapy, the disease progressed rapidly due to heavy tumor burden. The patient developed systemic complications and died shortly after discharge. This case underscores the diagnostic challenge in distinguishing aggressive lymphoma from inflammatory myopathies, particularly in immunocompromised individuals. Although HIV increases the risk of NHL, primary skeletal muscle involvement is rare and often misdiagnosed. Early biopsy is critical in patients with muscle-dominant symptoms and inconclusive autoimmune workup. This report emphasizes the need to consider lymphoma in the differential diagnosis of unexplained myopathic symptoms in HIV-positive patients.