Comparison of Clinical and Ultrasonographic Severity Assessment in Hidradenitis Suppurativa: Prognostic Implications

BACKGROUND: Accurate assessment of hidradenitis suppurativa (HS) severity is crucial for individualized management, yet conventional clinical grading may underestimate disease extent due to subclinical lesions. Ultrasound enables visualization of deep abscesses and tunnels and may provide additional prognostic information. MATERIALS AND METHODS: Sixty-eight patients with HS underwent standardized clinical and ultrasonographic evaluation. Disease severity was classified using the International Hidradenitis Suppurativa Severity Score System (IHS4) and the modified Sonographic Scoring of HS (mSOS-HS). Concordance between the two systems was assessed, and ultrasonographic grading and features were analyzed in relation to achievement of IHS4-55 at week 12. RESULTS: The mSOS-HS classified 18 patients (26.5%) as having more severe disease than IHS4. The two grading systems showed statistically significant agreement, with the Kappa value approaching the threshold for moderate agreement (Kappa = 0.395, 95% CI: 0.204-0.586, p < 0.001). Patients with higher mSOS-HS grades were less likely to achieve IHS4-55 at week 12 (p = 0.014). Among specific ultrasonographic features, the railway sign, defined as parallel hyperechoic lines within tunnel-like structures, was significantly associated with failure to achieve IHS4-55 (p = 0.003). CONCLUSION: Ultrasonography reveals subclinical HS involvement beyond clinical examination and provides prognostic information for treatment response. The mSOS-HS complements IHS4 for comprehensive disease staging, while the railway sign may serve as an imaging biomarker for unfavorable response across real-world treatment settings.