Hidradenitis suppurativa associated with spondyloarthritis -- results from a multicenter national prospective study.

OBJECTIVE: To determine the prevalence and characterize the inflammatory musculoskeletal symptoms of hidradenitis suppurativa (HS), a chronic inflammatory disease of skin appendages.

METHODS: Patients with HS referred to 3 dermatology university hospital centers were systematically screened for peripheral arthritis, dactylitis, inflammatory back pain, or enthesitis. After careful clinical examination, patients were further classified according to clinical and imaging criteria for spondyloarthritis (SpA) using the Amor, European Spondyloarthropathy Study Group (ESSG), and ASsessment in ankylosing spondylitis (ASAS).

RESULTS: We screened 640 patients with HS; 184 had musculoskeletal symptoms. In all, 43 (mean age 39.4 yrs, ± 8.3; 80% women) had arthritis, inflammatory back pain, or enthesitis and were investigated further. Signs of HS preceded the onset of articular symptoms in 39 patients (90%), at a mean interval of 3.6 years. A total of 18 (41%), 24 (55%), and 15 (34%) patients fulfilled the Amor, ESSG, and ASAS criteria, respectively, while synovitis, acne, pustolosis, hyperostosis, and osteitis (SAPHO) syndrome was established in 4 patients. The crude prevalence of SpA in all 640 patients with HS was 3.7% by the ESSG criteria.

CONCLUSION: SpA may occur in patients with HS, with the prevalence in this group exceeding that in the general population. The very short time between skin and joint symptom onset in some cases suggests common pathogenic mechanisms underlying HS and SpA.