Diagnostic Challenges in HHV-8-Associated Multicentric Castleman Disease in a Patient with Prior Kaposi Sarcoma.

Human herpesvirus-8 (HHV-8)-associated multicentric Castleman disease (MCD) is a rare lymphoproliferative disorder with systemic and cutaneous manifestations that can be diagnostically challenging, especially in immunocompromised patients. We report the case of a 68-year-old man with HIV and biopsy-proven Kaposi sarcoma (KS), who developed progressive fevers, night sweats, weight loss, and fatigue, accompanied by diffuse lymphadenopathy, splenomegaly, and new erythematous and hyperpigmented lesions shortly after intravenous immunoglobulin therapy for Guillain-Barré syndrome. A laboratory evaluation revealed that the patient had elevated total protein and polyclonal hypergammaglobulinemia, without monoclonality. Imaging demonstrated widespread lymphadenopathy and splenomegaly. A core lymph node biopsy showed polytypic plasmacytosis, but was non-diagnostic. Given the ongoing symptoms, an excisional biopsy was performed, revealing regressed germinal centers with increased interfollicular vascularity, mantle zone "onion skinning," and HHV-8 LANA-1 nuclear positivity, establishing the diagnosis of HHV-8-associated MCD. Rituximab monotherapy was initiated, resulting in clinical improvement, resolution of the constitutional symptoms, and stabilization of ascites. This case highlights the importance of maintaining a high index of suspicion for MCD in patients with KS who develop new systemic or cutaneous findings, the limitations of a core biopsy, and the value of a timely excisional biopsy in guiding diagnosis and treatment.