Successful treatment of idiopathic mast cell activation syndrome with low-dose Omalizumab

Objectives: Idiopathic mast cell disorders, a recently defined and recognised syndrome in clinical practice, are similar to the previously termed non-clonal mast cell disorder. Patients with idiopathic mast cell activation syndrome (MCAS) suffer all the classical signs of mast cell activation but do not have evidence of mast cell clonality. Furthermore, treatment of these patients can be limited and burdensome in those with refractory symptoms. Methods: Here, we describe treatment of a patient with idiopathic MCAS utilising a single monthly subcutaneous injection of omalizumab and review the current classification and therapeutic options for clonal and non-clonal MCAS. Results: Low-dose omalizumab treatment has successfully led to a 5-year, sustained clinical response, controlled debilitating symptoms of mast cell activation and allowed for reintroduction and long-term maintenance of bee venom subcutaneous immunotherapy. Conclusion: Low-dose omalizumab of 150 mg monthly should be considered for maintenance management of patients with idiopathic MCAS for its cost and quality-of-life benefits.