Validation of patient-reported outcomes in Parkinson's disease: comparisons of generic and disease-specific health-related quality of life instruments.

Health-related quality of life HRQOL is central to the management of chronic diseases such as Parkinson's disease PD. Several disease specific and generic instruments have been used to measure quality of life in PD, but nobody has to date identified which disease-specific or generic measure has the most relevant domains and optimal psychometric properties reliability, validity and sensitivity for use in the PD population. The aims of the study were therefore to compare the measurement properties of available instruments in PD population and recommend the most appropriate ones for use in future clinical research and routine practice. The UKSIP a generic HRQoL instrument which had not been previously assessed in the PD population or compared against the PDQ-39 demonstrated good test-retest reliability Spearman's r 0.70 and convergent validity p 0.001 of the UKSIP overall score with all domains of the PDQ-39 in a postal survey of PD patients n 91 mean age 70 64male. The UKSIP overall score correlated most strongly with the PDQ-39 mobility and activities of daily living scales. The strong Cronbach's a values 0.70 for the UKSIP physical and psychosocial summary scores gave an indication that their items were internally consistent. Interestingly, much of the dysfunction reported by PD patients was related to non-physical difficulties according to the UKSIP and vice versa for the PDQ-39. This study highlighted the robustness and reliability of the UKSIP in this PD population. When comparing the UKSIP against a benchmark generic instrument, the SF-36, in a sample of patients n 36 mean age 69 24male from a neurology out-patients clinic, it had comparable psychometric properties with a PD clinical measure of disease severity, the Hoehn and Yahr H Y scale. The two questionnaires were also able to discriminate between stage I, II and III/IV of PD as measured by the H Y scale p 0.05 for most domains. However, the UKSIP exhibited evidence of responsiveness to change over time in some domains of interest p 0.05 amongst patients reporting deterioration as assessed by the H Y scale, a pattern that was not repeated by the SF-36. Furthermore, items in the SF-36 were identified as redundant as they had little bearing in the elderly population whereas the UKSIP detected impairment in areas of interest to PD patients such as sexual activity, impairment in cognition, and sleep disturbance which are not addressed in the SF-36. Having established that the UKSIP was the more suitable generic instrument to use in PD the established disease-specific instrument, the PDQ-39 was assessed against the relatively new disease-specific Parkinson's Impact Scale PIMS. The PIMS exhibited varying levels of internal consistency reliability which were found to be erratic between baseline and follow-up visits n 47 mean age 65 25male. Also, the internal consistency of the PIMS column which was completed by fluctuating patients were wide-ranging a 0.284 - 0.731 for each of the PIMS dimensions at baseline. On the other hand, all PDQ-39 domains exhibited good internal consistency reliability Cronbach's a 0.70 which was stable across the baseline and follow-up visits. Though there was evidence of convergent validity for the PIMS with strong correlations with the PDQ-39 domain scores this was only for the non-fluctuating patients. Also, none of the correlation coefficients were found to be statistically significant at p 0.05 between PIMS domains and the clinical measure, the H Y, indicating a lack of association between this clinical outcome measure and the domains of HRQoL measured by the PIMS. The PDQ-39 exhibited strong correlation p 0.005 against the UPDRS score and against the H Y. The PIMS did highlight that there was a difference in dimension scores between stable and fluctuating patients. An important observation from this study was that the PIMS was not well comprehended by the PD patients as was reflected by the high rate of missing data in what is a relatively short instrument. The study which was conducted across four neurology out-patient centres n 145 mean age 65 80male revealed that the PDQ-39 was able to identify that patients with fluctuating disease and dyskinesia experience greater impairment in the relevant domains of HRQoL compared to stable patients, and in particular for the domain of emotional well-being. The responsiveness of the PDQ-39 was partially confirmed as levels of significance p 0.05 were reached for the domains of mobility in the motor fluctuation group with no dyskinesia and communication for the stable group, who were deemed to have deteriorated at the follow-up visit as indicated by an increase in the total UPDRS score. Finally, the study observed that greater caregiver distress was evident for the motor fluctuating and dyskinetic groups compared to the carers of the stable patients.