A 10-year-old girl presents to the emergency with high grade fever of 2-weeks duration and rashes over lower limbs for the last 7 days. Examination reveals mild pallor, generalized petechiae and hepatosplenomegaly. Investigations reveal: Hemoglobin 9 g/dL, total leucocyte count 2100/mm3, platelet count 20,000/mm3, peripheral smear shows pancytopenia, SGOT 50 IU/dL, SGPT 64 IU/dL, serum ferritin 1200 microgram/L, serum fibrinogen 100 mg/dL and serum triglycerides of 350 mg/dL. The most likely diagnosis is:
Hemophagocytic lymphohistiocytosis
Prolonged fever, hepatosplenomegaly, pancytopenia, hyperferritinemia, hypofibrinogenemia and hypertriglyceridemia fulfil the HLH-2004 diagnostic criteria for Hemophagocytic lymphohistiocytosis (HLH). Aplastic anemia does not cause hepatosplenomegaly or hyperferritinemia to this degree, and ITP would not explain the pancytopenia and organomegaly.