Systemic Mastocytosis: A Rare and Unusual Cause of Pancytopenia

Background: Systemic mastocytosis (SM) is a diverse condition characterised by abnormal growth and activity of clonal mast cells. It can have an extensive systemic and cutaneous involvement. Diagnosis is challenging because of variable and non-specific presentation, ranging from pruritus and hypotension to multi-organ manifestations, leading to delayed recognition. Case details: A 68-year-old female presented with frequent syncopal episodes, hemodynamic instability, and severe anaemia. Results: Initial investigations showed pancytopenia (Hb 2.9 g/dL, TLC 2.19 × 109/L, platelets 7 × 109/L) and splenomegaly (12 cm). A bone marrow biopsy was performed due to persistent pancytopenia, revealing a hypocellular marrow with dense infiltrates of spindle-shaped mast cells (16%). Immunohistochemistry with CD117 and toluidine blue confirmed mast cell infiltration. Total serum tryptase was elevated at 42 ng/mL. Conclusion: The patient was diagnosed with aggressive SM with features of mast cell degranulation and bone marrow infiltration. She was managed with low-dose glucocorticoids, packed red cell transfusions, and supportive care. This case highlights the challenges in diagnosing SM due to its non-specific, multi system clinical presentation and the need for high clinical suspicion.