Development and Psychometric Validation of the Pelvic Dystonia Severity Scale (PDSS)

Background. Chronic pelvic pain with involuntary pelvic-floor hypertonicity is common, disabling, and inconsistently measured, and no validated condition-specific severity instrument exists. A refractory subset has been proposed to represent a focal dystonia of the pelvic musculature, termed pelvic dystonia. Purpose. To develop the Pelvic Dystonia Severity Scale (PDSS) and evaluate its measurement properties as a patient-reported measure of pelvic-pain symptom severity and burden, following the COSMIN guidelines. Methods. Cross-sectional study with a test-retest component in 102 adults from an outpatient multidisciplinary pain practice. We assessed data quality, structural validity, internal consistency, test-retest reliability, measurement error, and construct validity against the Global Dystonia Severity Rating Scale (GDS) and Brief Pain Inventory (BPI). Because no validated diagnostic criteria exist, a clinician blinded to PDSS responses rated each participant for clinical signs of pelvic dystonia (present/possible/absent) as a provisional reference standard. Results. 100 of 102 participants (98%) returned complete data, with 0% item-level missing data. Factor analysis supported a unidimensional structure (single factor, 68.6% of variance; loadings 0.56-0.93), with high subscale intercorrelations (r = 0.81-0.97). Internal consistency (Cronbach's 0.810-0.924) and test-retest reliability (ICC 0.857-0.953) were strong. Convergent validity was supported by correlations with GDS pelvic-region items (r = 0.56-0.68) and BPI severity (r = 0.44-0.55), and discriminant validity by weak correlations with anatomically remote regions (shoulder/arm r = 0.03-0.16). PDSS scores rose monotonically across blinded clinical-signs categories (absent 14.9, possible 32.7, present 52.0; Kruskal-Wallis p < 0.001), discriminating signs-present from signs-absent participants with a very large effect (Hedges g = 2.19; ROC AUC = 0.92). Conclusion. The PDSS is a psychometrically robust, unidimensional measure of pelvic-pain symptom severity and burden with strong data quality, reliability, and construct validity. It is suitable for characterizing symptom severity and, pending responsiveness testing, for monitoring treatment. The dystonia interpretation of the underlying phenotype is discussed as a hypothesis for future neurophysiologic and longitudinal study.