A comparative analysis of chronic inducible urticaria in 423 patients: Clinical and laboratory features and comorbid conditions

Background: Chronic inducible urticaria (CIndU) is a subtype of chronic urticaria (CU) which require specific physical or non-physical triggers to occur. They may be isolated or may coexist with chronic spontaneous urticaria (CSU). Despite their frequent appearance in dermatology clinics, there is scarce information on the distinguishing features among the most common subtypes of CIndU as well as isolated CIndU versus CSU plus CIndU. Objectives: To compare clinical and laboratory characteristics, and comorbid conditions among the most common CIndU types and isolated CIndU versus CSU plus CIndU. Methods: We retrospectively analysed CIndU patients and compared patients' demographic, clinical and laboratory characteristics across isolated CIndU, CSU plus CIndU, symptomatic dermographism (SD), cold urticaria (ColdU) and cholinergic urticaria (ChoU). Results: A total of 423 patients (similar to 70% isolated CIndU, similar to 30% CSU plus CIndU, similar to 5% mixed CIndU subtypes) were included in the study. The most frequent CIndU subtypes were SD (68.6%; 290/423), ColdU (11.4%; 48/423) and ChoU (10.9%; 46/423). Isolated CIndU patients were younger than CSU plus CIndU (33.74 +/- 12.72 vs. 37.06 +/- 11.84, p = 0.010). Angioedema, emergency referrals, need for systemic steroids, comorbid systemic disorders were more frequent and baseline urticaria control test scores were lower in CSU plus CIndU patients (vs. CIndU, p < 0.001, p = 0.008, p < 0.001, p = 0.031, p = 0.036, respectively). Among CIndU subtypes, ChoU patients were younger (24.9 +/- 12.2 vs. 34.47 +/- 12.12 vs. 31.38 +/- 14.95; p < 0.001) and had male predominance (p < 0.001) while SD patients had no angioedema (p < 0.001) and had higher frequency of increased total IgE levels (p = 0.006). Conclusions: Isolated CIndU and CSU plus CIndU seems to be different endotypes of CU where CSU plus CIndU presents a more severe and refractory course. There are distinctive features of each CIndU subtype. These suggest involvement of different pathomechanistic pathways in these subtypes that need to be clarified in future studies.