High prevalence of hidradenitis suppurativa symptoms in axial spondyloarthritis patients: A possible new extra-articular manifestation.

BACKGROUND: Spondyloarthritis (SpA), a chronic inflammatory, rheumatic disease, and hidradenitis suppurativa (HS), a chronic, debilitating, inflammatory skin disease, share several clinical and pathophysiological features, such as the association with inflammatory bowel disease and elevated cytokine levels IL-17 and TNF-α. Recently, SpA was reported to be more prevalent (2.3-28.2%) in patients with HS than in the general population. Conversely, the prevalence of HS in SpA is not exactly known.

OBJECTIVE: To determine the prevalence of HS in patients with axial SpA, a subtype of SpA primarily of the axial skeleton. Secondly, to identify patient characteristics associated with the presence of HS in axial SpA.

METHODS: In this cross-sectional study, a self-screening questionnaire based on validated diagnostic HS questions was sent to all participating axial SpA patients from the Groningen Leeuwarden Axial Spondyloarthritis (GLAS) cohort fulfilling the ASAS axial SpA criteria. Self-reported HS symptoms were confirmed by previous medical diagnosis or verification by phone using highly specific validated questions.

RESULTS: In total, 75.6% (449/592) questionnaires were eligible for analyses. Included patients had a mean age of 50 ± 13 years, 64% was male, mean symptom duration was 23 ± 13 years, and 79% was HLA-B27 positive. HS diagnosis could be confirmed in 41 patients, resulting in an estimated prevalence of 9.1%. In comparison to patients without a positive history of HS, these patients were more often female (54% vs. 35%, P = 0.02), showed higher axial SpA disease activity (mean BASDAI 4.5 vs. 3.6, p = 0.01 and ASDASCRP 2.6 vs. 2.2, P = 0.003) and worse quality of life (QoL) (median ASQoL 9.0 vs. 4.0, P < 0.001). Also, a history of heel enthesitis and dactylitis was more prevalent (34% vs. 19%, P = 0.03 and 15% vs. 6%, P = 0.05, respectively). Multivariable analysis showed that a higher score on ASDAS was independently associated with HS (OR: 1.639, 95% CI: 1.176-2.284).

CONCLUSION: In our cohort of axial SpA patients, HS is more prevalent than in the general population (9.1% versus 0.053-4.1%). HS is associated with female gender, lower QoL, and especially higher axial SpA disease activity.