Omalizumab, an anti-IgE antibody, is an efficient treatment for chronic spontaneous urticaria (CSU) and asthma. Moreover, Omalizumab has demonstrated efficacy in treating allergic rhinitis, atopic dermatitis and, more recently, in nasal polyps. So we could suppose that it could be efficient in other mast cell activating disorders (MCAD) as mast cell activation syndrome (MCAS), indolent systemic mastocytosis (ISM) and extracutaneous signs of CSU (CSU+).

We retrospectively collected data from all ISM, MCAS or CSU+ patients treated with Omalizumab and followed by the Department of clinical immunology of Grenoble-Alpes University Hospital, France. We report the evolution of extracutaneous symptoms in CSU+ MCAS and ISM patients treated with Omalizumab. Since 2014, 23 patients were included in our study: 8 ISM, 2 MCAS and 13 CSU+.

The median age of our cohort was 48 years (17-81). The median age of patients having their first symptoms was 33 years (range: 6-68) and when the diagnosis was made was 45 years (range: 13-77). Before Omalizumab therapy, the major debilitating symptoms are angioedema (70 %), urticaria (83 %), gastro-intestinal (GI) symptoms (70 %) and recurrent anaphylactic reaction (35 %). Among patients, 5 (23 %) were treated with a median dose of 300mg/3 weeks, 11 (50 %) received a dose of 300mg/month and 6 a dose of 300mg/15 days (27 %). For our available data, extracutaneous symptoms were improved for all patients except for one. The improvement appeared 3 months post-treatment (range 1- 12). Patients also noticed an asthenia improvement (31 %). Omalizumab was given during a median period of 17 months (range: 5-62) with no serious adverse events. The most common drug side effects were local swelling at the site of injection (4 %), transient asthenia (30 %), fainting attack (13 %), arthralgia (8 %).

In conclusion, MCAD are relatively rare and heterogeneous diseases with poor therapeutic option. Omalizumab, an anti-IgE Ab, seems to be safe and efficient in several symptoms. It also seems to be efficient in CSU+ extracutaneous symptoms.