Multicenter validation of the Italian Pain in Dystonia Scale in idiopathic adult-onset cervical dystonia

Background: The Pain in Dystonia Scale (PIDS) is a self-administered instrument to assess pain in dystonia, validated in cervical dystonia (CD). Objective: To translate and culturally adapt the PIDS into Italian following a standardized forward-backward procedure and to validate the resulting Italian version (I-PIDS) in patients with idiopathic adult-onset CD as part of a multicenter effort aimed at evaluating its clinimetric properties across dystonia subtypes. Methods: I-PIDS was completed by 64 Italian patients with cervical dystonia from 16 centers, three months or more after their last botulinum toxin treatment. Standard clinimetric analyses were performed. Results: Acceptability was optimal, with no missing data. Score distributions met expected criteria, with mean-median differences <10% of the maximum score for all body regions except the jaw, and no floor or ceiling effects. Internal consistency was satisfactory for all pain regions (α = 0.81-0.91) and for functional impact (α = 0.83) and modulating factors (α = 0.73-0.74). Convergent validity was demonstrated by a moderate correlation between neck pain scores and the Global Dystonia Rating Scale (r = 0.39, p = 0.03), while divergent validity was supported by the absence of correlation with the Montreal Cognitive Assessment (r = 0.02, p = 0.90). Exploratory analyses suggested that pain severity in CD was not associated with age, sex, education, age at onset, or dystonia duration, and that pain frequently involved multiple body regions, independently of dystonia distribution. Conclusions: These findings support the validity of I-PIDS and provide further insight into the pattern of pain in CD.