Rare Peritoneal Involvement in Adult T-Cell Leukemia/Lymphoma: A Diagnostic Conundrum

We present the case of a 60-year-old Caribbean man with no significant past medical history who presented to the emergency department with a three-week history of progressive, diffuse abdominal pain associated with early satiety and unintentional weight loss. Vital signs were stable, and physical examination revealed abdominal distension and diffuse tenderness without peritoneal signs. Laboratory studies were notable for elevated lactate dehydrogenase and mild leukocytosis. Computed tomography followed by PET-CT imaging demonstrated multiple nodular soft tissue densities with increased fluorine-18 fluorodeoxyglucose (18F-FDG) uptake throughout the mesentery, peritoneum, and bilateral pleural surfaces, raising concern for peritoneal lymphomatosis. An ultrasound-guided biopsy of an omental implant was performed, revealing large atypical lymphoid cells positive for CD3, CD2, and CD4, and negative for CD5, CD7, and CD8, with a Ki-67 proliferation index of 90%, consistent with an aggressive peripheral T-cell lymphoma. Peripheral blood RT-PCR returned positive for human T-cell lymphotropic virus type 1 (HTLV-1), aligning with the diagnosis of acute adult T-cell leukemia/lymphoma (ATLL), stage IV. The patient's clinical course was rapidly progressive and marked by complications including spontaneous tumor lysis syndrome, recurrent episodes of malignant small bowel obstruction, and gram-negative bacteremia. While preparing for treatment with dose-adjusted etoposide phosphate, vincristine sulfate (Oncovin), cyclophosphamide, and doxorubicin hydrochloride (hydroxydaunomycin) (EPOCH) chemotherapy, he suffered a cardiac arrest during central venous catheter placement. Despite resuscitation efforts, he sustained an anoxic brain injury and died 32 days after the initial presentation. This case highlights an aggressive presentation of ATLL with peritoneal involvement and underscores the challenges of rapid disease progression and acute complications, as well as the importance of considering endemic exposure history, utilizing PET-CT for identifying extranodal disease, and rapidly confirming diagnosis through biopsy.