Schneeweiss MC, et al. - A population-based cohort study was conducted to investigate the risk of developing inflammatory arthritis among individuals with HS compared with matched individuals without HS. They applied longitudinal claim data from commercially insured individuals, including those with Medicaid and Medicare, covering 185 million lives in the United States between January 1, 2003, and January 1, 2016. All ages individuals were distinguished, who received a diagnosis of HS (International Classification of Diseases, Ninth Revision code 705.83 or International Statistical Classification of Diseases and Related Health Problems, Tenth Revision code L73.2), described as 1 diagnosis by a dermatologist or 3 diagnoses by any health care professional. For the non-HS group, they risk-set sampled 2 individuals without HS from all plan enrollees who did not have a diagnosis of HS matched on the date the individual with HS entered the cohort. They eliminated individuals who had less than 180 days of continuous enrollment before cohort entry or had preexisting inflammatory arthritis, enrolling ankylosing spondylitis, psoriatic arthritis, other spondyloarthritis, or rheumatoid arthritis (eAppendix in the Supplement). This study was approved by the Brigham and Women’s Hospital’s Institutional Review Board. All individual information was deidentified.