Objective: To develop a new rating instrument for pain in AOID and validate it in the most common form of AOID, cervical dystonia (CD).

Background: Adult-onset isolated dystonia (AOID) is associated with a complex spectrum of non-motor symptoms. Cervical dystonia (CD) is the most common focal AOID, characterized by chronic abnormal, involuntary posturing of the head, neck, and shoulders. Pain is its most frequent non-motor symptom, with a prevalence ranging from 54.6% to 88.9% (1). It is mainly perceived in the neck and shoulders but often spreads to the upper back region, and sometimes radiates cranially on the side of head deviation and caudally to the ipsilateral upper limb (2). The nature and pathophysiology of pain in AOID remains incompletely understood. Better recognition and understanding of pain in AOID are needed to design and implement adequate and effective therapeutic strategies (3,4,5). As one important step in this process, validated and specific screening and severity rating scales are needed.

Method: The development and validation of the Pain in Dystonia Scale (PIDS) comprised three phases. In phase 1, international experts and participants with AOID generated and evaluated the preliminary items for content validity. In phase 2, the PIDS was drafted and revised by the experts, followed by cognitive interviews to ensure suitability for self-administration. In phase 3, the PIDS psychometric properties were assessed in 85 participants with CD and retested in 40 participants.

Results: The final version of PIDS evaluates pain severity (by body-part), functional impact and external modulating factors. Test-retest reliability showed a high-correlation coefficient for the total score (0.9, p<0.001), and intraclass correlation coefficients were 0.7 or higher for all items in all body-parts sub-scores. The overall PIDS severity score showed high internal consistency (Cronbach’s alpha 0.9). Convergent validity analysis revealed a strong correlation between the PIDS severity score and the TWSTRS pain subscale (0.8, p<0.001), the BPI-sf items related to pain at time of the assessment (0.7, p<0.001) and impact of pain on daily functioning (0.7, p<0.001).

Conclusion: The PIDS showed excellent psychometric characteristics and may become a valuable tool in clinical practice, providing for the first time a comprehensive evaluation of pain in AOID. Future steps will include validation in other types of AOID.

References: 1. Marciniec M, Szczepańska-Szerej A, Papuć E, Rejdak K. Targeting pain in the long-term treatment of cervical dystonia with botulinum toxin A. Int J Neurosci. 2022 Oct 3;132(10):1026–30.
2. Albanese A. The clinical expression of primary dystonia. J Neurol. 2003 Oct 1;250(10):1145–51.
3. Avenali M, De Icco R, Tinazzi M, Defazio G, Tronconi L, Sandrini G, et al. Pain in focal dystonias – A focused review to address an important component of the disease. Parkinsonism Relat Disord. 2018 Sep;54:17–24.
4. Chudler EH, Dong WK. The role of the basal ganglia in nociception and pain. Pain. 1995 Jan;60(1):3–38.
5. Tinazzi M, Squintani GM, Bhatia KP, Segatti A, Donato F, Valeriani M, et al. Pain in cervical dystonia: Evidence of abnormal inhibitory control. Parkinsonism Relat Disord. 2019 Aug;65:252–5.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-pain-in-dystonia-scale-pids-development-and-validation/