Objective: To develop a short, practical instrument that is sensitive to the specific cognitive deficits in Parkinson's disease (PD) for comparing groups in research situations and for assessing change in cognitive functioning over time.
Methods: A literature search was conducted to identify the most frequently affected cognitive domains in PD and to select candidate items for the initial scale. This scale was tested in 85 patients and 75 age-, education-, and sex-matched control subjects. Items that met predefined criteria for data quality, reproducibility, and discriminative properties were included in the final scale.
Results: The final scale, the SCOPA-COG (SCales for Outcomes of PArkinson's disease-cognition), consists of 10 items with a maximum score of 43, with higher scores reflecting better performance. The test-retest reliability of the total score was 0.78 (intraclass correlation coefficient) and ranged from 0.40 to 0.75 for individual items (weighted kappa). Cronbach's alpha was 0.83. Construct validity of the scale was supported by the expected correlations with the CAMCOG (Cambridge Cognitive Examination) and the Mini-Mental State Examination (MMSE) and by differences found between groups of participants classified by dementia status and between patients grouped by disease severity. The scale showed a clear trend toward lower cognition scores for patients with more advanced PD. The coefficient of variation of the SCOPA-COG was higher than that of the CAMCOG or the MMSE, indicating a better ability to detect differences between individuals.
Conclusion: The SCOPA-COG is a short, reliable, and valid instrument that is sensitive to the specific cognitive deficits in PD.