Development and validation of a disease-specific scale for the assessment of quality of life in patients with Gilles de la Tourette Syndrome: the GTS-QOL

Background. Gilles de la Tourette Syndrome (GTS) is a chronic neuropsychiatric disorder characterised by multiple motor and phonic tics and associated behavioural problems, with a serious impact on the health-related quality of life (HR-QOL) of patients. However, little is known on the perception of HR-QOL by patients with GTS, and no patient reported HR-QOL measures have been proposed for this population. Aim. The objective of this study is the development and validation of a new scale for the quantitative assessment of HR-QOL in patients with GTS. Methods. A pool of 40 potential scale items was generated based on interviews with 120 GTS outpatients, literature review, and consultation with experts. These items were administered, in the form of a questionnaire, to a sample of 192 patients attending the Tourette Clinic, National Hospital for Neurology and Neurosurgery, London, along with standardised clinical scales. Validated psychometric methods were used to develop a rating scale satisfying standard criteria for reliability and validity. Results. Response data analysis and item reduction methods led to a final 27-item GTS-specific HR-QOL scale (GTS-QOL) with four subscales, addressing the psychological, physical, obsessional, and cognitive domains, respectively. The psychometric properties of the GTS-QOL were further tested in a second sample of 136 subjects recruited through the UK-Tourette Syndrome Association. The GTS-QOL demonstrated satisfactory scaling assumptions and acceptability; both internal consistency reliability and test-retest reliability were high (Cronbach's alpha ≥0.8 and intraclass correlation coefficient ≥0.8); validity was supported by interscale correlations (range 0.5-0.7), repeated factor analysis, and correlation patterns with other rating scales and clinical variables. Conclusion. The GTS-QOL is proposed as a new disease-specific patient-reported scale for the measurement of HR-QOL in patients with GTS, taking into account the complexity of the clinical picture of GTS