Systemic mastocytosis results from proliferation and activation of an abnormal mast cell clone. It is a heterogeneous disorder with clinical manifestations ranging from skin lesions alone to aggressive multi-organ infiltration and decreased survival. Given these varied manifestations, diagnosis can be difficult. We describe the case of a woman who presented with rash and diarrhoea and had a history of anaphylactic reactions. Over a protracted period, the patient’s symptoms were investigated by a number of specialties including gastroenterology, dermatology, immunology and haematology. Morphological, immunohistochemical and molecular analysis of bone marrow samples ultimately led to a diagnosis of systemic mastocytosis. Management with leukotriene and histamine antagonists resulted in significant improvement in symptoms and quality of life. The case serves to highlight the protean manifestations of systemic mastocytosis, the tests available to diagnose it and the agents available to treat it.
