A Diagnostic Challenge in Regional Australia: Concurrent Mycobacterium avium Complex Lymphadenitis and Hairy Cell Leukemia.

Introduction: Hairy cell leukemia is a rare, indolent chronic B cell lymphoproliferative disorder characterized by cytopenia, splenomegaly and profound immune dysfunction, predisposing affected individuals to opportunistic infections including non-tuberculous mycobacteria. Concurrent presentation with disseminated mycobacterial infection is un-common and may pose significant diagnostic challenges. Case Presentation: We report the case of a 68-year-old Caucasian man with a history of splenectomy who presented with fever, lymphadenopathy, leukopenia and a generalized rash. Initial investigations including infectious, hematological and vasculitis workups were inconclusive. Lymph node histology demonstrated necrotizing lymphadenitis, which in the context of an otherwise negative investigations was initially suggestive of Kikuchi-Fujimoto disease. Subsequently, cultures from lymph node tissue and blood yielded Mycobacterium avium complex, establishing a diagnosis of disseminated infection. Further bone marrow evaluation with flow cytometry ultimately confirmed underlying hairy cell leukemia. Conclusions: This case highlights how an impaired immune milieu may obscure classic clinical and histopathological features, contributing to diagnostic delay and potentially inappropriate immunosuppressive treatment. Clinicians should maintain a high index of suspicion for underlying hematological malignancy in patients presenting with unexplained cytopenia in association with atypical infections. Early consideration of bone marrow evaluation can be crucial.