Hidradenitis suppurativa and rheumatoid arthritis: evaluating the bidirectional association

Despite some common pathogenic themes, the association of hidradenitis suppurativa (HS) and rheumatoid arthritis (RA) has been poorly investigated. We aimed to evaluate the bidirectional association between HS and RA. A population-based study was conducted to compare HS patients (n = 6779) with age-, sex- and ethnicity-matched control subjects (n = 33,260) with regard to the incidence of new-onset and the prevalence of preexisting RA. Adjusted hazard ratios (HRs) and adjusted odds ratios (ORs) were estimated. The prevalence of preexisting RA was greater among patients with HS relative to controls (0.5% vs 0.3%. respectively; p = 0.019). The odds of being diagnosed with HS were 1.6-fold higher in patients with a history of RA (fully-adjusted OR, 1.66; 95% CI, 1.11–2.49; p = 0.014). The incidence rate of new-onset RA was estimated at 4.3 (95% CI, 2.5–6.8) and 2.4 (95% CI, 1.8–3.2) cases per 10,000 person-years among patients with HS and controls, respectively. The risk of RA was comparable between patients with HS and controls (fully-adjusted HR, 1.45; 95% CI, 0.77–2.72; p = 0.249). Compared to other patients with HS, those with HS and comorbid RA were older, had a higher prevalence of diabetes mellitus, hypertension, and hyperlipidemia, and had a comparable risk of all-cause mortality. In conclusions, a preexisting diagnosis of RA predisposes individuals to develop HS. Clinicians managing patients with HS and RA should be aware of this association. Further research is required to delineate the underlying pathomechanism of this observation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12026-021-09221-4.