Systemic Mastocytosis — RACP Adult Medicine MCQ

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HardHaematologySystemic MastocytosisRACP Adult Medicine

A 35-year-old man presents with recurrent bouts of abdominal pain, diarrhoea, and flushing. His symptoms are triggered by stress and alcohol. CT abdomen is normal. Serum tryptase during an episode is markedly elevated at 45 µg/L (normal <11.4). Baseline tryptase is also elevated at 25 µg/L. What should be investigated?

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Correct answer: D — Medullary thyroid carcinoma

Persistently elevated baseline serum tryptase (>20 µg/L) with paroxysmal symptoms (flushing, abdominal pain, diarrhoea) should raise suspicion for systemic mastocytosis. The WHO diagnostic criteria require bone marrow biopsy showing multifocal dense mast cell aggregates, spindle-shaped mast cells, aberrant CD25 expression, and/or KIT D816V mutation. Tryptase >20 µg/L is a minor criterion. Carcinoid syndrome has elevated 5-HIAA, not tryptase.

Reference: eTG – 2025 – Haematology; WHO – 2022 – Mastocytosis Classification