Preliminary Validation of the Early Sacroiliitis Screening Tool ( <scp>ESHST</scp> ) for Identifying Hidradenitis Suppurativa Patients at High Risk of Spondyloarthritis

BACKGROUND: Hidradenitis suppurativa (HS) is increasingly recognized as a systemic inflammatory disease associated with spondyloarthritis (SpA). However, validated screening tools for SpA in dermatology practice are lacking. We therefore developed the Early Sacroiliitis Screening Tool (ESHST), an eight-item symptom-based questionnaire for early SpA identification in HS. METHODS: In this prospective, cross-sectional, preliminary validation study, 100 consecutive HS patients (median age 36.5 years, 72% male) were enrolled in a tertiary-care setting. All participants underwent blinded rheumatologic evaluation, HLA-B27 testing, and sacroiliac imaging. Magnetic resonance imaging (MRI) findings were independently evaluated by two blinded rheumatologists with consensus adjudication of discrepant cases. Diagnostic performance of the ESHST was assessed using receiver operating characteristic analysis and logistic regression. RESULTS: SpA was diagnosed in 20% of patients (axial 13%, peripheral 7%). Median ESHST scores were significantly higher in patients with SpA than in those without SpA [10 (8-12) vs. 2 (0-4), p < 0.001]. The ESHST showed excellent discrimination (area under the curve [AUC] 0.930, 95% confidence interval [CI] 0.860-0.983). At a cutoff ≥ 8, sensitivity was 85.0% (95% CI 62.1-96.8), specificity was 92.5% (95% CI 84.4-97.2), positive predictive value was 73.9% (95% CI 51.6-89.8), negative predictive value was 96.1% (95% CI 89.0-99.2), and overall diagnostic accuracy was 91.0% (95% CI 83.6-95.8). SpA prevalence increased across ESHST risk categories (low 10%, intermediate 25%, high 75%). CONCLUSION: The ESHST demonstrated promising preliminary diagnostic performance as a dermatology-oriented screening tool for identifying HS patients at increased risk of SpA. External validation in larger multicenter and ethnically diverse populations is required before broader clinical implementation.