Sustained improvement in urticaria pigmentosa and pruritus in a case of indolent systemic mastocytosis treated with cladribine

Summary Systemic mastocytosis ( SM ) is a myeloproliferative disorder, characterized by a clonal proliferation of abnormal mast cells accumulating in internal organs and sometimes in the skin, leading to cutaneous and systemic symptoms. Mutations within the gene KIT , which encodes the receptor tyrosine kinase ( KIT ) on mast cells, is found in most patients with SM . We report a case of a 62‐year‐old woman presenting with a pruritic rash on her limbs and trunk. Several years later she developed gastrointestinal symptoms, associated with raised serum tryptase. Skin and bone marrow biopsies confirmed a diagnosis of SM , initially presenting with urticaria pigmentosa. Responses to multiple therapies, including potent topical steroids, oral antihistamines, phototherapy and the tyrosine kinase inhibitor, nilotinib, were inadequate. Treatment with cladribine (2‐chlorodeoxyadenosine) produced a marked and sustained reduction in her symptoms and serum tryptase level.