Supplementary Material for: Clinical Characteristics, Management, and Natural History of Chronic Inducible Urticaria in a Pediatric Cohort

Background: Some forms of chronic urticaria (CU) can be specifically attributed to a response to a definite trigger, referred to as chronic inducible urticaria (CIndU). We aimed to assess the demographics, clinical characteristics, comorbidities, natural history, and management of pediatric patients with CIndU. Methods: Over a 6-year period, children presenting to the allergy clinic at the Montreal Children’s Hospital (MCH) with CIndU were prospectively recruited. CU was defined as the presence of wheals and/or angioedema, occurring for at least 6 weeks. A standardized diagnostic test was used to establish the presence of a specific form of urticaria. Resolution was defined as the absence of hives for 1 year without treatment. Results: Sixty-four patients presented with CIndU, of which 51.6% were male, with a median age of 12.5 (interquartile range 7.3, 15.9) years. Cold CU and cholinergic CU were the most common subtypes (60.3 and 41.3%, respectively). Basophil counts were undetectable in 48.4% of the cases, and C-reactive protein levels were elevated in 7.8% of patients. Of all cases, 71.4% were controlled with second-generation antihistamines. The resolution rate was of 45.3% (95% confidence interval 33.1–57.5%), based on per-protocol population within the 6-year course of the study. Resolution was more likely in patients who presented with well-controlled urticaria control test scores and elevated CD63 counts and in those suffering from thyroid comorbidity. Conclusion: The natural history of CIndU resolution in pediatric patients was relatively low and was associated with elevated CD63 levels, as well as thyroid comorbidity.