A 5-year-old child presents with a history of fever off–and–on for past 2 weeks and petechial spots all over the body and increasing pallor for past 1 month. Examination reveals splenomegaly of 2 ems below the costal margin. The most likely diagnosis is –

Pallor (anemia), petechial spot (thrombocytopenia), fever (infection due to neutropenia) with splenomegaly suggest the diagnosis of acute leukemia. Further, the presence of splenomegaly eliminates aplastic anaemia and ITP as the possibilities "Splenomegaly and lymphadenopathy are extremely uncommon in ITP and their presence should lead one to consider other possible diagnosis". - Robbin's "Splenomegaly is characteristically absent in aplastic anemia and if present the diagnosis of a plastic anemia should be seriously questioned". Hypersplenism is a condition characterised by splenomegaly and cytopenias with a normal hyperplastic marrow and response to splenectomy. Although cytopenias resulting from hypersplenism may give rise to most manifestations mentioned in the question these are more likely with massively enlarged spleens and not with minimally enlarged spleen as in the question above (2cm below costal margin in a 2 year old child).