New-Onset Musculoskeletal Manifestations in Hidradenitis Suppurativa: A Large-Scale Incidence Analysis.

Background Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease traditionally considered cutaneous in nature. Emerging data suggest HS may also have systemic inflammatory effects, including musculoskeletal involvement, yet large-scale studies evaluating incident joint disease following HS diagnosis are limited. Objective To quantify the 12-month incidence of new-onset musculoskeletal manifestations, including synovitis, enthesopathy, and small joint pain, among patients with newly diagnosed HS. Methods We conducted a retrospective cohort study using the TriNetX US Collaborative Network, analyzing electronic health records from 71 healthcare organizations. Patients aged 18-40 years with newly diagnosed HS and no prior history of joint disease were included. Outcomes assessed within 12 months of HS diagnosis included synovitis, tenosynovitis, enthesopathy, and small joint pain. Kaplan-Meier survival and frequency analyses were performed. Results Among 125,181 patients with HS, 1.2% developed synovitis or enthesopathy, and 2.3% developed small joint pain within one year of diagnosis. Kaplan-Meier survival probabilities at 12 months were 98.5% for synovitis/enthesopathy-free survival and 97.2% for small joint pain-free survival. The median number of outcome instances per patient was 1, with mean instances of 2.14 and 2.24, respectively. Conclusion This large-scale cohort study demonstrates that HS is associated with an early risk of musculoskeletal involvement, reinforcing its classification as a systemic inflammatory condition. Clinicians should monitor for joint-related symptoms in HS patients, particularly within the first year of diagnosis, to enable timely intervention and prevent progression.