Impact of smoking on disease severity and treatment outcomes in hidradenitis suppurativa

Background: Smoking is associated with hidradenitis suppurativa (HS), but the clinical significance of smoking history is poorly understood. Objectives: To examine the impact of smoking history and change in smoking behaviour on disease severity and treatment outcomes in patients with HS. Methods: Patients with hospital-diagnosed HS from two independent prospective cohorts, the Copenhagen Hidradenitis Suppurativa Cohort (HIS-COP) and the Danish Skin Cohort (DSC), were included. Data on Hurley stage, International Hidradenitis Suppurativa Severity Score System (IHS4), Dermatology Life Quality Index (DLQI), boil-associated pain and disease-related bother were extracted from HIS-COP to assess the association between smoking status at baseline and treatment outcomes. The DSC was used to assess the effect of change in smoking status on self-reported disease severity and DLQI. Results: In HIS-COP (n = 787), current smoking (53.9%) was associated with being Hurley stage III relative to I (OR = 2.38, 95% CI: 1.02–5.56, p = 0.044), higher IHS4 (OR = 1.05, 95% CI: 1.01–1.10, p = 0.018), higher DLQI (OR = 1.06, 95% CI: 1.03–1.09, p < 0.001) and greater overall disease-related bother (OR = 1.14, 95% CI: 1.07–1.22, p < 0.001) relative to never smokers when adjusted for. Increasing pack years smoked and the number of cigarettes smoked per day were significantly associated with higher IHS4 (p < 0.01 and p < 0.05, respectively); however, after adjusting for age and sex, p > 0.05. Among patients initiated on tetracycline-class treatment, current smokers had a significantly smaller mean (SD) reduction in IHS4 (2.5 (3.2) vs. 4.7 (4.9), p < 0.001), DLQI (4.2 (6.2) vs. 6.0 (6.4), p < 0.05) and percentage reduction in overall disease-related bother (2.9 (4.0) vs. 4.3 (4.0), p < 0.05), compared to non-smokers at follow-up. Smoking cessation and initiation both showed a trend towards increased self-reported disease severity after 12 months follow-up; however, data were limited. Conclusions: Smoking is associated with greater disease severity, poorer quality of life and worse treatment outcomes among patients with HS.