Idiopathic mast cell activation syndrome in real-life practice: clinical features and management

<b>Background:</b> Idiopathic mast cell activation syndrome (iMCAS) is a rare challenging diagnosis, and its treatment is not well standardized. <b>Objective:</b> This study aimed to evaluate the clinical features of iMCAS and the potential need of omalizumab in clinical practice. <b>Methods:</b> The clinical features and treatment regimens in 21 patients with iMCAS were evaluated. The number of anaphylaxis episodes, symptom severity scores via the visual analog scale (VAS), the disease control via the Likert scale were recorded at baseline, 6th-month and 1st-year visits. <b>Results:</b> The affected organ systems were the skin (100%), respiratory (90%), cardiovascular (76.2%), and neurologic (40%). Nineteen patients (90.5%) experienced a grade V anaphylaxis and received adrenaline at baseline. The median (interquartile range [IQR]) serum tryptase level during an episode and at baseline were 11.7 ng/mL (10.4-14.6 ng/mL) and 5.29 ng/mL (3.32-8.62 ng/mL), respectively. Nineteen patients (90.5%) required omalizumab due to unresponsiveness to other treatments at a median (IQR) duration of 3 years (1-4 years). By the end of 1 year, nine patients (47.4%) continued on 150 mg, seven patients (36.8%) continued on 300 mg, two patients (10.5%) continued on 450 mg, and one patient (5.2%) continued on 600 mg of omalizumab. Overall, the VAS scores significantly decreased at the 6th month and 1st year of omalizumab treatment compared to both the time of diagnosis (6th month vs. diagnosis: p = 0.001; 1st year vs. diagnosis: p = 0.012) and the initiation of omalizumab treatment (6th month vs. initiation: p = 0.001; 1st year vs. initiation: p = 0.001). The number of anaphylaxis episodes was significantly higher at the time of diagnosis compared with the 6th month (p = 0.001) and 1st year (p = 0.001) of omalizumab treatment and the number of anaphylaxis episodes at the initiation of omalizumab treatment was significantly higher compared with the 6th month of omalizumab treatment (p = 0.001) and the 1st year of omalizumab treatment (p = 0.001). Symptom control levels on the Likert scale at the 6th month and 1st year of omalizumab treatment were found to be significantly higher compared to both the time of diagnosis (6th month vs. diagnosis: p = 0.001; 1st year vs. diagnosis: p = 0.001) and the initiation of omalizumab treatment (6th month vs. initiation: p = 0.001; 1st year vs. initiation: p = 0.001). <b>Conclusion:</b> The iMCAS causes severe anaphylaxis episodes that can be successfully prevented by omalizumab as an add-on treatment to other treatment options.