D3.413 - Basophil Activation Test Positivity and Response to Ciclosporin in Chronic Spontaneous Urticaria: A Real-World Exploratory Study

Chronic spontaneous urticaria (CSU) comprises distinct immunological endotypes. A subset of patients is thought to have autoimmune (type IIb) CSU, characterized by functional autoantibodies capable of activating basophils. The basophil activation test (BAT) has been proposed as a functional biomarker of this endotype. Ciclosporin, an immunomodulatory agent recommended as third-line therapy in refractory CSU, may be particularly effective in autoimmune-driven disease. The objective was to explore the association between BAT positivity and clinical response to ciclosporin in patients with refractory CSU.

We conducted a retrospective single-center study including adult CSU patients treated with ciclosporin who had available BAT results. Clinical characteristics, laboratory parameters, and patient-reported outcomes were collected. Treatment response was defined as Urticaria Control Test (UCT) ≥12 and/or improvement ≥5 points from baseline (ΔUCT ≥5). Dermatology Life Quality Index (DLQI) was analyzed when available.

Six female patients (median age 47; std 14.3) with CSU treated with ciclosporin were included.

Overall, 3/6 patients met response criteria.

Two patients had a positive BAT (33%). Among BAT-positive patients, marked clinical improvement was observed, including one case with UCT improvement from 5 to 16 (ΔUCT=11) and DLQI reduction from 9 to 0. BAT-negative patients demonstrated heterogeneous responses to ciclosporin.

In this real-world cohort, BAT-positive CSU patients showed substantial clinical improvement under ciclosporin therapy, supporting the biological plausibility of BAT as a marker of autoimmune CSU and potential predictor of response to immunomodulatory treatment. These findings are hypothesis-generating and limited by small sample size and retrospective design. Prospective studies with standardized outcome assessment are warranted to clarify the predictive value of BAT for ciclosporin response in CSU.