Nemolizumab as an Alternative Therapeutic Option for Indolent Systemic Mastocytosis.

Indolent systemic mastocytosis (ISM) is a clonal mast cell disorder characterized by recurrent symptoms that can persist despite treatment with antihistamines, leukotriene antagonists, and mast cell stabilizers. Treatment options are limited when symptoms remain refractory, and avapritinib is contraindicated or declined. We describe the case of a 62-year-old female with an 11-year history of ISM who developed worsening pruritus and urticaria despite extensive conservative and biologic therapies, including topical corticosteroids, hydroxyzine, montelukast, omalizumab, and dupilumab. Given her history of stroke, she declined avapritinib. Nemolizumab was initiated with a 60 mg loading dose followed by 30 mg every four weeks. After 12 doses, she achieved complete resolution of pruritus. This report suggests that nemolizumab may represent a potential therapeutic option for refractory ISM when standard therapies fail or targeted KIT inhibition is not feasible.