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

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.