Summary scores as well as the subdimensions of the PDQ-39 were calculated according to the scoring algorithm.17 The akinesia score of the UPDRS was calculated as the sum of item 19 and 23 to 26 of the UPDRS for both sides, the score of axial features from items 27 to 30, and the tremor score from items 20 and 21 for both sides. The tremor dominant subtype of Parkinson’s disease was defined as patients with a ratio of tremor to bradykinesia score (bradykinesia rigidity and postural instability subscores from the matchtips UPDRS motor scale and history) of 0.5 or more, and the akinetic rigid subtype as patients with a ratio of<0.5. Socioeconomic groups were determined according to the classification of occupations and coding index with socioeconomic group 1 representing the highest and group 5 the lowest socioeconomic class.18
Mean values were compared by the Mann-Whitney test, and Spearman rank correlation coefficients were calculated to assess the direction and magnitude of association between variables. Stepwise multiple regression analysis was used to determine the factors that best accounted for variance in QoL scores. Due to the number of different comparisons, statistical significance was only accepted at p<0.005.
Among all patients seen (n=202), 124 were classified as having probable Parkinson’s disease. The response rate was 78% ( questionnaires). There was no significant difference between responders and non-responders for age, disease duration, sex, Hoehn and Yahr stage, and Schwab and England score (p>0.05). Five questionnaires were returned with incomplete data (<50% of the QoL instrument), and were not used for further analysis. The characteristics of the responders are given in table 1.
Patients with high levels of depression (with BDI scores>17), a mini mental state score of 24 or less (out of 30),12postural instability on examination (as described in the UPDRS), and a history of falls or of gait difficulties had significantly worse PDQ-39 summary index scores than patients without these features (table 2). QoL scores of patients with the akinetic rigid subtype of Parkinson’s disease were also worse than those with tremor dominant disease. This difference could not be explained by older age or longer disease duration, as age and disease duration were similar between those with tremor dominant and those with akinetic rigid Parkinson’s disease. The difference of QoL scores between those with and those without a history of hallucinations just failed to reach significance (p=0.026; table 2). No difference in PDQ-39 scores was found between men and women and between patients with or without a poor (subjectively<50%) initial or current response to antiparkinsonian medication. A history of dyskinesias or fluctuations, incontinence, orthostatic symptoms, insomnia, pain, speech or swallowing impairment, a family history of Parkinson's disease, and symptom at onset had no significant impact on QoL scores. There was also no difference between those who were unemployed or had retired early due to the disease and those who were not, those with disease onset before or after the age of 50, and those with current age older than 60 or 70.
CORRELATIONS Out-of Health-related Ratings With PDQ-39
The PDQ-39 summary index correlated significantly and positively (r=0.68, p<0.001) with depression as measured by the BDI score and negatively with disability as measured by the Schwab and England scale (r=?0.66, p<0.001). Significant correlations were also obtained with disease severity as measured by the Hoehn and Yahr scale (r=0.6, p<0.001), the UPDRS motor subscore of axial features (r=0.57, p<0.001), the total UPDRS motor score (r=0.41, p<0.001), and the MMSE (r=?0.32, p<0.001). Correlations with duration of disease and age were not significant (r=0.18, p=0.19 andr=0.14, p=0.25, respectively), and akinesia score (r=0.3, p=0.028) and socioeconomic groups (r=0.25, p=0.023) just failed to correlate significantly with QoL.