Predicting the Speed of Response to Omalizumab in Chronic Spontaneous Urticaria

<b><i>Introduction:</i></b> Two distinct chronic spontaneous urticaria (CSU) endotypes, IgE-mediated autoallergic and IgG-mediated autoimmune, were defined based on the response patterns to omalizumab. However, the coexistence of IgE and IgG autoantibodies in a subset of patients might complicate the prediction of the treatment outcomes. This study aimed to evaluate the effectiveness and safety of omalizumab in CSU patients, focusing on the factors predicting the response patterns. <b><i>Methods:</i></b> This was a retrospective cross-sectional single-center study investigating CSU patients treated with omalizumab for at least 6 months between September 2015 and February 2023. Patients were evaluated regarding demographics, clinical findings, baseline laboratory parameters, treatment outcomes, and side effects. Early and late responders were defined depending on the time for response, within or after 3 months, respectively. <b><i>Results:</i></b> Among 82 patients, 75 (91.5%) responded to omalizumab during the first 6 months, classified as early (<i>n</i> = 51) and late responders (<i>n</i> = 24). The IgG anti-thyroid peroxidase (anti-TPO)/total IgE ratio was an independent predictor for determining the speed of response (<i>p</i> &lt; 0.05). Of 29 patients who discontinued omalizumab, 19 (65.5%) experienced relapse with a good response to retreatment (<i>n</i> = 18/19, 94.7%). Early responders relapsed more frequently than late responders (77.3% vs. 28.6%) (<i>p</i> &lt; 0.05). Only mild side effects were observed in a minority of patients (<i>n</i> = 8/82, 9.8%). <b><i>Conclusion:</i></b> Omalizumab is an effective and safe treatment in CSU. The IgG anti-TPO/total IgE ratio seems a valuable tool to predict the early and late responders, the former having a higher possibility of relapse upon drug withdrawal.