Exploring the Link Between Hidradenitis Suppurativa and Inflammatory Arthritis

Patients with hidradenitis suppurativa (HS) carry a high risk for numerous comorbidities, according to a growing body of research on the topic. Among the co-occurring disorders affecting this patient population, including metabolic syndrome mental health disorders, recent studies highlight a possible link between HS and several types of inflammatory arthritis such as rheumatoid arthritis (RA).¹

The inflammatory nature of these diseases likely represents the key mechanism underlying the observed overlap. “Both HS and inflammatory arthritis are characterized by a role of cytokines such as IL-6, IL-1beta, and TNF,” explained S. Louis Bridges, Jr., MD, PhD, physician-in-chief and chair of the department of medicine at Hospital for Special Surgery (HSS), chief of the division of rheumatology at both HSS and New York-Presbyterian/Weill Cornell Medical Center, the Franchellie M. Cadwell Professor of Medicine at HSS, and the Joseph P. Routh Professor of Rheumatic Diseases in Medicine at Weill Cornell Medical College in New York.²

“The importance of TNF in HS and inflammatory arthritis is supported by the FDA approval of the TNF inhibitor adalimumab for treatment of HS–and this drug is also approved for a variety of other conditions including RA, psoriatic arthritis, and seronegative spondyloarthritis,” he said in an interview with us.³

Genetic susceptibility and environmental factors have also been implicated in the interaction between the 2 diseases.⁴

Summary of Evidence

“Based on published data, HS patients have a 3-fold increased risk of developing inflammatory arthritis–especially spondyloarthritis,” stated Saakshi Khattri, MD, a board-certified rheumatologist, dermatologist, and internist, and associate professor in the department of dermatology at the Icahn School of Medicine at Mount Sinai Health System in New York.⁴

In a 2021 meta-analysis of 7 studies with a pooled total of 200,361 patients  with HS and 385,599 control participants, Almuhanna et al observed an increased overall risk for inflammatory arthritis in patients with HS vs control participants (odds ratio [OR], 3.44; 95% CI, 1.92–6.17) as well as associations between HS and spondyloarthritis (SpA) (SpA; OR, 2.10; 95% CI, 1.40–3.15), HS and axial SpA in particular (OR 1.89; 95% CI, 1.14–3.12), and HS and RA (OR, 1.96; 95% CI, 1.28–2.98).⁴

Similarly, a meta-analysis published in 2022 demonstrated a greater prevalence of RA, SpA, and psoriatic arthritis (PsA) among patients with HS compared to the general population. Some of the data examined indicated a greater risk for inflammatory arthritis in HS patients who are male, younger than 30 years, or taking adalimumab or infliximab, and in those with severe HS.⁵

Regarding SpA specifically, a 2020 population-based cohort study of 70,697patients with HS and 141,412 matched patients without HS showed an elevated risk for ankylosing spondylitis (incidence rate [IR], 0.60 vs 0.36 per 1000; hazard ratio [HR], 1.65; 95% CI, 1.15-2.35), PsA (0.84 vs 0.58 per 1000; HR, 1.44; 95% CI, 1.08-1.93), and RA (4.54 vs 3.86 per 1000; HR, 1.16; 95% CI, 1.03-1.31) in patients with HS compared to non-HS patients.⁶

In a 2018 cross-sectional study, a greater number of patients with HS were diagnosed with SpA compared with control participants (28.2% vs 2.6%; OR, 11.0; 95% CI, 4.1-83.3; P =.02). In addition, in the HS group, the HLA-B27 antigen was associated with a diagnosis of SpA.⁷

A cross-sectional study published in 2019 found a higher prevalence of HS in a cohort of patients with axial SpA (9.1%) compared with the general population (0.053%-4.1%). The results also revealed an independent association between HS and greater SpA disease activity as indicated by Ankylosing Spondylitis Disease Activity Score (ASDAS) results (OR, 1.639; 95% CI, 1.176-2.284).²

These findings of these 2 studies align with earlier results linking HS and SpA.¹

“Other studies have looked at association between HS and RA, including a population-based study which showed a greater prevalence of preexisting RA among patients with HS relative to controls,” Dr Khattri told us. The 2021 study aimed to elucidate the bidirectional relationship between HS and RA and found that the odds of subsequent HS diagnosis were 1.6-fold higher among RA patients compared with matched control participants (fully-adjusted OR, 1.66; 95% CI, 1.11–2.49; P =.014).⁸

Clinical Implications and Next Steps

Despite the accumulating evidence suggesting an increased risk for various types of inflammatory arthritis in HS, there is currently “significant variability in reports on the incidence and prevalence of these diseases in HS, due to differences in study design and selection bias,” Dr Bridges noted. “In addition, there are no standard diagnostic criteria for HS, which leads to differences in case definition across reports,” he said.

Although he does not believe the available evidence is sufficient to support the routine practice of informing dermatology patients with HS that they have an elevated risk of developing arthritis, he says this could change with the emergence of further epidemiological evidence.

The study authors of existing research on the topic emphasize the importance of physician awareness regarding the connection between HS and arthritis, and they encourage collaboration between dermatologists and rheumatologists in treating patients with bothdisorders.^5,6

Dr Khattri suggests that it may be prudent to inquire about arthritis symptoms in patients with HS. Research has shown that onset of arthritis symptoms may occur 1 to 20 years following the appearance of skin lesions in HS.⁴

“Dermatologists should definitely ask HS patients about symptoms of inflammatory arthritis such as morning stiffness–especially if it lasts more than 30 minutes and improves with motion–and stiffness in the lower back after prolonged immobility, like being seated at a desk for long time,” she advised. These symptoms should raise suspicion for the possibility of inflammatory arthritis and prompt a referral to a rheumatologist for a formal evaluation.

In terms of remaining gaps in this area, Dr Bridges cites the need for “well-designed, large, rigorous epidemiological studies, including those examining population-based data, to more definitively prove or refute” the link between HS and inflammatory arthritis. “If the associations are confirmed, then additional studies focused on cytokines and cell populations of HS and arthritis patients should be conducted to look for similarities and differences in the pathogenesis of these inflammatory diseases.”

Dr Khattri also noted ongoing needs pertaining to HS in general, including more FDA-approved treatments and increased awareness of HS to promote earlier detection of the disease, as many patients with HS experience extended delays (roughly 7 years) in the time to diagnosis.⁹