The significance of hypersensitivity to autologous sweat and serum in cholinergic urticaria: Cholinergic urticaria may have different subtypes

Background: The pathogenesis of cholinergic urticaria (ChU) has been unclear except for the involvement of acetylcholine. Attempts to classify ChU according to etiology have rarely been performed. Objective: To evaluate the significance of responsiveness to autologous sweat and serum in ChU in relation to their clinical characteristics. Methods: This study involved 18 patients diagnosed with ChU between January 2010 and April 2011 in the Catholic Medical Center-St. Paul's Hospital. History taking included symptom duration, association with atopy, decreased sweat secretions, seasonal variation, and response to treatment. Intradermal autologous serum skin test (ASST) and autologous sweat skin test (ASwST) and basophil histamine release test with sweat were done. Results: Sweat hypersensitivity was proven by a positive ASwST and basophil histamine release test in only 37.5% of patients with ChU, and in none of the healthy controls. The weal size of ASwST correlated with percentage basophil histamine release. A positive response to autologous serum was displayed by 38.9% of patients, whereas 10% of healthy controls showed a positive ASST response. Intriguingly, patients with a positive ASwST had a negative ASST, and vice versa. Despite this, there was no difference in the clinical characteristics between positive ASST and positive ASwST groups. Conclusions: The frequency of hypersensitivity to autologous sweat and serum was significantly higher in patients with ChU, compared with healthy controls. This suggests that autoimmunity to an unknown serum factor as well as sweat hypersensitivity may be involved in the pathogenesis of ChU.