This report documents a young female patient with microgranular variant acute promyelocytic leukaemia (APL) harbouring FLT3-ITD mutation who presented with fatigue, fever, gum bleeding and altered sensorium. Despite prompt initiation of all-trans retinoic acid and arsenic trioxide therapy, she developed worsening respiratory distress and neurological deterioration, succumbing within 70 hours of admission. Postmortem examination revealed extensive extramedullary leukaemic infiltration in the liver, heart, brain parenchyma and meninges, confirming widespread disease beyond the commonly recognised medullary involvement. This case highlights the diagnostic challenges in differentiating extramedullary APL from haemorrhagic complications and differentiation syndrome. Our literature review reveals that extramedullary involvement in APL at diagnosis is rare but clinically significant, with skeletal and central nervous system (CNS) being the most common sites. The optimal management strategies remain undefined, particularly for CNS-directed therapy. This case underscores the importance of considering extramedullary involvement in APL patients with atypical or rapidly progressive presentations.
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