Disseminated fusariosis presenting as persistent febrile neutropenia in acute myeloid leukaemia: a diagnostic challenge

Disseminated fusariosis is an uncommon but highly lethal opportunistic fungal infection that occurs predominantly in patients with haematological malignancies and prolonged neutropenia. Early diagnosis is challenging because its clinical manifestations frequently overlap with those of more common causes of febrile neutropenia. A middle-aged man with newly diagnosed acute myeloid leukaemia harbouring a FLT3-internal tandem duplication mutation was treated with azacitidine, venetoclax, and gilteritinib. Despite guideline-directed empirical antimicrobial therapy and antifungal prophylaxis, he developed persistent febrile neutropenia without an identifiable focus on conventional investigations. Whole-body positron emission tomography-computed tomography demonstrated multiple fluorodeoxyglucose-avid lesions involving the skin, skeletal muscles, and bones. Histopathological examination of an intramuscular lesion revealed invasive septate fungal hyphae, and subsequent blood cultures yielded Fusarium species, confirming disseminated fusariosis. Combination antifungal therapy with liposomal amphotericin B and voriconazole was initiated. However, the patient developed progressive septic shock and multiorgan failure and ultimately died. Disseminated fusariosis should be considered in immunocompromised patients with persistent unexplained fever and evolving cutaneous lesions despite broad-spectrum antimicrobial therapy and antifungal prophylaxis. PET-CT may help identify occult sites of infection, guide tissue sampling, and facilitate diagnosis when the source of persistent fever remains unclear.