ABSTRACT
OBJECTIVE: To develop and validate a disease-specific instrument to measure health-related quality of life in patients with oromandibular dystonia. DESIGN: Prospective, cross-sectional observational study. SETTING: Tertiary referral clinic, North East England, UK. METHODS: The Oromandibular Dystonia Questionnaire (OMDQ-25) was evaluated in a group of 30 patients for psychometric properties, including its sensitivity to change after Botulinum Toxin A treatment. Comparison to a generic instrument was enabled using the Glasgow Health Scale Inventory and the Glasgow Benefit Inventory (GBI). RESULTS: Item generation passed tests for scaling assumptions. Reliability was proven (Cronbach's α > 0.78; test-retest > 0.9) and validity supported with both convergent validity and discriminant validity. Sensitivity to change after Botulinum Toxin A treatment was established for all subscales (P ≤ 0.005), and in comparison with the GBI, all subscales showed large effect sizes. CONCLUSION: The Oromandibular Dystonia Questionnaire (OMDQ-25) is the first reliable and valid instrument to measure health-related quality of life in patients with oromandibular dystonia.