The Pain in Dystonia Scale (PIDS)—Validation in Craniofacial and Upper Limb Dystonia

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BACKGROUND: Pain is one of the most disabling non-motor symptoms in adult-onset isolated dystonia (AOID). The Pain in Dystonia Scale (PIDS) was developed and validated in cervical dystonia. Its applicability to other focal subtypes remains unknown. OBJECTIVES: To validate the PIDS in patients with craniofacial and upper limb dystonia, expanding its use beyond cervical dystonia. METHODS: We conducted a two-phase cross-sectional validation study in independent cohorts from Calgary, Canada and Italy. The Calgary pilot cohort (n = 20) included participants with craniofacial and/or upper limb dystonia who completed the PIDS twice for test-retest reliability and a battery of comparator scales. The Italian cohort (n = 109) was recruited through the Italian Dystonia Registry and completed the PIDS after cross-cultural adaptation. Internal consistency, test-retest reliability, construct validity, and distribution properties were assessed using established psychometric standards. RESULTS: Pain was highly prevalent (90.0% Calgary; 96.3% Italy), with anatomical distribution varying by dystonia subtype. Internal consistency was high across both cohorts (Cronbach's alpha 0.82-0.96), with minimal floor and ceiling effects. Test-retest reliability in the pilot cohort was excellent (ICC = 0.85). Construct validity was supported by strong correlations between PIDS scores and established pain and quality-of-life measures. Functional impact and pain modulators were consistently reported across cohorts, with stress identified as the most frequent aggravating factor and rest and stretching as common relieving factors. CONCLUSIONS: The PIDS demonstrates reliability, validity, and feasibility in craniofacial and upper limb dystonia, supporting its adoption for evaluating dystonia-related pain in clinical and research settings across the main focal subtypes.

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