“ Hidradenitis suppurativa (HS) was once believed to be a disease limited to the skin, but current knowledge shows that it is a systemic inflammatory disorder associated with several comorbidities, such as cardiovascular disease, depression, and inflammatory arthritis,” explains Nouf Almuhanna, MD. “Since inflammatory arthritis can cause progressive joint destruction, leading to functional disability, recognition by dermatologists of this association is important for early detection, which can hopefully prevent further progression and complications. Previous studies, however, show inconsistent associations between HS and inflammatory arthritis, indicating a wide range of prevalence from 3.7% to 52.5%.”

Link Between HS & Arthritis Explored

For a paper published in Dermatology (Karger), Dr. Almuhanna and colleagues aimed to address these inconsistencies and investigate the association between HS and inflammatory arthritis. A systematic review and meta-analysis were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to identify the association between HS and inflammatory arthritis, spondyloarthritis, ankylosing spondylitis (AS), and rheumatoid arthritis (RA).

Three-Fold Increased Risk for Arthritis

Seven studies were included in the analysis, totaling 200,361 patients with HS and 385,599 controls. The pooled analyses illustrated a significantly increased risk of inflammatory arthritis in patients with HS compared with controls (odds ratio [OR], 3.44; 95% CI 1.92-6.17). There was also a statistically significant association between HS and spondyloarthritis (OR, 2.10; 95% CI, 1.40-3.15) and between HS and AS, (OR, 1.89; 95% CI 1.14-3.12). Moreover, the pooled analysis showed a significant association between HS and RA (OR, 1.96; CI 95% CI 1.28-2.98). “Our findings show that patients with HS have a significant, three-fold increased risk for inflammatory arthritis and are specifically at a higher risk for spondyloarthritis, its subtype AS, and RA,” says Dr. Almuhanna (Figure). “When examined by type of inflammatory arthritis, patients with HS had 2.1-fold increased odds for having spondyloarthritis, 1.96-fold increased odds of having RA, and 1.89-fold increased odds of having AS.” Across the studies, HS was reported predominantly in females, consistent with previous literature, according to the researchers. Severity of HS, however, has been shown to be associated with males, which may explain why comorbid inflammatory arthritis, linked to HS severity, has also been reported to occur predominantly in males. The researchers note that the exact mechanisms underlying the interaction between HS and inflammatory arthritis remains unknown. Possible explanations, they write, include genetic susceptibility, immune dysregulation, cytokine abnormalities, and environmental factors.

Early Referral to Rheumatologists Is Crucial

“Dermatologists treating patients with HS should, therefore, be mindful of patients with HS presenting with symptoms of inflammatory arthritis, such as morning stiffness, lower back pain, and peripheral joint pain,” Dr. Almuhanna says. “Patients with HS should be informed about the increased risk of inflammatory arthritis and be referred to a rheumatologist for an early screening. Furthermore, the onset of skin lesions in HS usually precedes the arthritis symptoms by 1 to 20 years, raising the importance of early detection of joint involvement.” Dr. Almuhanna and colleagues note that their analysis was limited by the incorporation of a proportionally small number of studies. There was also no clear definition in the included studies for HS severity, which may have varied between the studies and impacted the prevalence of arthritis in patients with HS. “We would like to see future research include a larger number of studies and focus on the association between HS severity and existence of inflammatory arthritis,” says Dr. Almuhanna. “Additionally, randomly controlled trials are needed to examine treatment options for patients with HS with comorbid inflammatory arthritis.”