Secondary haemophagocytic lymphohistiocytosis vs methotrexate toxicity - a diagnostic conundrum.

A 74-year-old female with a background of rheumatoid arthritis, managed with weekly methotrexate, was admitted with; oedema, dyspnoea, cachexia and jaundice. Bloods revealed pancytopenia, hyperferritinaemia, hyperbilirubinaemia, hypoalbuminaemia and hypofolataemia. Imaging showed a large right-sided pleural effusion, requiring therapeutic aspiration, and splenomegaly. Bone marrow aspirate revealed haemophagocytosis. Differential diagnoses included methotrexate toxicity (MTXT) and haemophagocytic lymphohistiocytosis (HLH). Management was initiated for MTXT whilst ongoing investigation for possible HLH continued.