The development of the Tuebingen Cushing's disease quality of life inventory (Tuebingen CD-25). Part I: construction and psychometric properties.

OBJECTIVE: To develop a disease-specific questionnaire for Cushing's disease (CD), the Tuebingen Cushing's disease quality of life inventory (Tuebingen CD-25).
METHODS: Sources for item generation consisted of technical literature, interviews with patients and the rating of neurosurgeons, endocrinologists and a neuropsychologist. A preliminary inventory with 64 items was handed out to 63 CD patients. Twenty-eight patients filled out the questionnaire preoperative, the remaining 35 patients evaluated their health-related quality of life (HRQoL) retrospectively. Item reduction and scale generation followed the principles of classical test theory. Validation was performed with the WHOQoL-BREF.
RESULTS: The final version of the Tuebingen CD-25 contained 25 items, showed high reliability (Cronbach's alpha = 0.93) and validity (r = -0.65) and includes the subdomains Depression, Sexual Activity, Environment, Eating Behaviour, Bodily Restrictions and Cognition. The retrospective rating of the Tuebingen CD-25 showed similar results compared to the pretreatment group. We found a non-linear correlation between the Tuebingen CD-25 scores and patients' age, younger (21-30 years) and middle-aged (51-60 years) patients having inferior HRQoL than patients between 31 and 50 years and older than 61 years. Preoperative 24 h urinary free cortisol (UFC) levels correlated significantly with the subscale Cognition and only marginally failed significance level for the subscale Eating Behaviour, while preoperative cortisol and ACTH levels did not correlate with any scale.
CONCLUSION: The Tuebingen CD-25 is a valid and reliable instrument to evaluate HRQoL in CD. Based on impairment of HRQoL for the different subdimensions, specific support can be offered to the patients.