Use of the Rash Appearance to Distinguish Cholinergic Urticaria Subtypes: A Retrospective Cohort Study.

Background: Cholinergic urticaria (CholU) is characterized by pruritic papular wheals induced by various temperature-elevating stimuli such as exercise, bathing, and emotional stress. Although it is considered important to classify CholU into subtype on the basis of the pathogenesis and clinical features for better management, few studies have evaluated the rash type as a clinical feature.

Aim: This study aimed to investigate the associations between different types of rashes in CholU and their clinical phenotypes, and to consider the mechanisms underlying each type of rash.

Methods: We conducted a retrospective study of 64 patients diagnosed with CholU who visited the Dermatological Institute of Kobe University Hospital. Clinical and photographic data obtained after exercise provocation and/or thermoregulatory sweat tests were reviewed and used to classify patients into the red wheal/erythema group (n = 44) or the goosebumps group (n = 20). Intradermal tests, namely the autologous sweat skin test (ASwST) and autologous serum skin test (ASST), were performed to assess sweat and serum reactivity, respectively. The presence of atopic dermatitis and hypohidrosis was evaluated in accordance with established guidelines. Univariable logistic analyses were conducted to assess the associations between rash types and clinical features, namely age, sex, ASwST and ASST results, atopic dermatitis, hypohidrosis, pruritus, and pain. Multivariable logistic analysis was performed using only sex and age. Statistical analyses were performed using GraphPad Prism 10, with significance set at P < 0.05.

Results: The red wheal/erythema group had typical punctate or coalescent erythematous wheals, while the goosebumps group had follicular, goosebump-like rashes with or without erythema. Compared with the red wheal/erythema group, the goosebumps group had a higher proportion of males (85% versus 38.6%) and higher prevalences of hypohidrosis (89.4% versus 35.7%) and pain (89.5% versus 37.8%). In contrast, the red wheal/erythema group had significantly higher prevalences of ASwST positivity (68.4% versus 20%), atopic dermatitis (58.1% versus 5.3%), and pruritus (78.4% versus 10.5%). Univariable analysis revealed that ASwST positivity, atopic dermatitis, and pruritus were significantly associated with the red wheal/erythema group, while hypohidrosis and pain were significantly associated with the goosebumps group. Multivariable logistic analysis showed that male sex was significantly associated with the goosebumps group.

Conclusions: Patients with CholU develop rashes with varying coloration and shapes. Goosebump-like rashes, which differ from typical wheals, were often accompanied by hypohidrosis. The type of rash may help to differentiate the clinical subtypes of CholU.