Disseminated Mycobacterium immunogenum-associated Hemophagocytic Lymphohistiocytosis after Stem Cell Transplantation

Secondary hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome most commonly triggered by infection, malignancy, or transplant-related immune dysregulation. Rapidly growing mycobacteria are uncommon causes of disseminated infection and have only rarely been reported as infectious triggers of HLH. A 56-year-old immunocompromised woman with a history of allogeneic hematopoietic stem cell transplant presented with recurrent fever, progressive transaminitis, and laboratory features consistent with secondary HLH. Liver biopsy showed granulomatous hepatitis with iron overload. Initial treatment with dexamethasone and anakinra resulted in transient clinical improvement. Less than 2 weeks later, she was readmitted with worsening hepatic dysfunction and found to have acid-fast bacilli in blood and bone marrow cultures, later identified as Mycobacterium immunogenum. Despite targeted antimicrobial therapy, the patient developed progressive hepatic and renal failure and died. To our knowledge, this case represents the first reported case of disseminated M. immunogenum infection precipitating secondary HLH, expanding the recognized clinical spectrum of this rapidly growing nontuberculous mycobacterium and highlights the diagnostic challenges of atypical mycobacterial infection in immunocompromised hosts.