Omalizumab Reduced Anaphylaxis Burden in Patients With Idiopathic MCAS

Omalizumab was associated with significant reductions in symptom burden and anaphylaxis frequency among patients with idiopathic mast cell activation syndrome (iMCAS), according to a study evaluating real-world treatment outcomes in a challenging and poorly standardized condition.

Idiopathic mast cell activation syndrome is characterized by recurrent mast cell activation without an identifiable underlying cause. Because of its rarity and clinical heterogeneity, treatment approaches remain variable.

The study evaluated 21 patients with iMCAS and assessed clinical manifestations, treatment patterns, symptom severity, disease control, and anaphylaxis frequency over time. Skin involvement was present in all patients, while respiratory, cardiovascular, and neurologic manifestations occurred in 90%, 76.2%, and 40% of patients, respectively.

Severe reactions were common. Nineteen patients (90.5%) experienced grade V anaphylaxis and required adrenaline treatment at baseline. Median serum tryptase levels increased from 5.29 ng/mL at baseline to 11.7 ng/mL during episodes.

Most patients ultimately required biologic therapy. According to the investigators, 19 patients (90.5%) required omalizumab because of inadequate response to other treatments, with treatment initiated after a median duration of 3 years following diagnosis.

At 1 year, maintenance doses varied, with 47.4% of patients receiving 150 mg, 36.8% receiving 300 mg, 10.5% receiving 450 mg, and 5.2% receiving 600 mg of omalizumab.

Clinical outcomes improved significantly after treatment initiation. Visual analog scale symptom scores decreased at both 6 months and 1 year compared with diagnosis and omalizumab initiation (all P ≤ .012). The number of anaphylaxis episodes also declined significantly at 6 months and 1 year (all P = .001).

Disease control improved as well. Likert scale assessments demonstrated significantly higher symptom control at both follow-up visits compared with baseline and treatment initiation (all P = .001).

The authors concluded that “iMCAS causes severe anaphylaxis episodes” and that these events “can be successfully prevented by omalizumab as an add-on treatment to other treatment options.”

Reference
Hormet Igde M, Korkmaz P, Toprak ID, et al. Idiopathic mast cell activation syndrome in real-life practice: clinical features and management. Allergy Asthma Proc. 2025;46(4):314-322. doi:10.2500/aap.2025.46.250025