LONG TERM TREATMENT OF SYSTEMIC MASTOCYTOSIS WITH OMALIZUMAB

Introduction Systemic mastocytosis (SM) is a rare condition resulting from chronic and episodic mast cell release involving extracutaneous sites. Although currently not FDA approved for the treatment of SM, omalizumab may help in the prevention of anaphylaxis and disease burden in SM. We describe the long term successful response of a patient with SM to treatment with omalizumab. Case Description A 32-year-old female with a diagnosis of SM and urticarial pigmentosa, initially diagnosed with idiopathic anaphylaxis in 2009, continued to have recurrent episodes of anaphylaxis that occurred 1-2 times monthly and chronic skin rashes. No triggers for reactions were identified to include foods, supplements, medications, insect stings, exercise and latex exposure. The patient met WHO classification for SM by the presence of multifocal, dense aggregates of mast cells (>25%) in the bone marrow with surface expression positive for CD2 and CD25 and persistently elevated serum tryptase levels (134, 151, 159 ng/mL). Despite therapy with Zantac 150 mg BID, Zyrtec 10 mg BID, Singulair 10 mg daily and cromolyn sodium 200 mg, the patient continued to have recurrence of anaphylaxis requiring epinephrine and prednisone. In May 2016, she was started on omalizumab 300 mg subcutaneous injections Q4Weeks. Since then, the patient has only had one episode of anaphylaxis with a significant improvement in her cutaneous symptoms. Discussion This case shows a long term substantial improvement in frequency of anaphylactic episodes and cutaneous symptoms in a patient with SM treated with omalizumab.