Development and validation of the disease-specific QOL-CD quality of life questionnaire for patients with Cushing's disease

OBJECTIVECushing’s disease (CD) patients experience a range of debilitating symptoms that impair quality of life (QOL) as assessed using generic measures. These generic measures are inadequate to capture the disease-specific burden of illness. The development of the CD-specific QOL-CD measure of QOL using items generated by CD patients and healthcare professionals will provide a holistic assessment of patient outcomes and efficacy of novel therapies.METHODSA total of 96 CD patients participated. A list of 177 items (version 1.0) was generated by treated CD patients (n = 9), caregivers (n = 2), healthcare providers (n = 7), and results of a MEDLINE search. Item reduction was performed through content analysis and dual scaling. Patients’ rating of importance was incorporated to reduce to a final version of 56 items (version 3.0). Evidence for test-retest reliability was sought through administering the QOL-CD 1 week apart and Cronbach’s α of each subscale. Construct validity was assessed through extreme group analysis and comparison with the normal Canadian population. Concurrent validity was sought through comparison with the SF-36, Functional Assessment of Cancer Therapy–Brain (FACT-Br), and Karnofsky Performance Status (KPS). Perioperative testing was conducted on CD patients (n = 25) against nonfunctioning pituitary adenoma controls (n = 25) through pre- and postoperative testing.RESULTSA total of 96 CD patients (86 females and 10 males; mean age 45.23 ± 14.16 years) participated. The QOL-CD was feasible (mean completion time 15 minutes, with 70% believing accurate capture of QOL), reliable (CD 1 week apart: r = 0.86; control 1 week apart: r = 0.83; Cronbach’s α: general health = 0.73, emotional health = 0.85, physical health = 0.78, mental status = 0.82, social well-being = 0.63, medical treatment = 0.54), and valid (extreme group testing p < 0.001; SF-36 and QOL-CD general health: r = 0.56, social well-being: r = 0.21, emotional health: r = 0.61, total score: r = 0.58; FACT-Br and QOL-CD physical health: r = 0.47, social well-being: r = 0.21, emotional health: r = 0.34, total score: r = 0.68; KPS and QOL-CD general health: r = 0.32, total score: r = 0.14). Perioperative testing of CD patients (n = 25) demonstrated improvement in all subscales postoperatively, with a significant difference in emotional health (p < 0.001) and physical health (p < 0.001).CONCLUSIONSThe QOL-CD questionnaire has been developed for patients with CD and has demonstrated evidence for validity and reliability.