Development and validation of an alternative version of the Parkinson's Disease-Cognitive Rating Scale (PD-CRS).

INTRODUCTION: The Parkinson's Disease-Cognitive Rating Scale (PD-CRS) is a valid and reliable instrument to screen for and diagnose mild cognitive impairment in PD (PD-MCI) and to monitor potential outcomes in clinical trials. Although this scale shows adequate sensitivity to change in non-demented PD patients, an alternative form (AF) with proven reliability could minimize practice effects associated with repeated testing.

METHODS: We selected PD-CRS/AF items following the criteria proposed in the original PD-CRS. We assessed a prospective sample of 75 non-demented PD patients (normal cognition, n = 50; PD-MCI, n = 25) using both tools, administered on two consecutive days, in a randomized order.

RESULTS: The PD-CRS/AF showed a high internal consistency (Cronbach's α = 0.80). Differences between total mean scores were not significant. Floor/ceiling effects were acceptable. The discriminative power for MCI was high for both tools (area under the curve 0.91; 95% CI, 0.84-0.98 for PD-CRS; 0.88, 95% CI, 0.80-0.96 for PD-CRS/AF). Receiver operating curve analysis showed the optimal cut-off point of the two versions to discriminate PD-MCI from PD-normal cognition was ≤81 (PD-CRS = sensitivity 94%, specificity 73%; PD-CRS/AF = sensitivity 92%, specificity 73%).

CONCLUSIONS: Our results suggest that the PD-CRS/AF is a valid and reliable instrument to complement the original PD-CRS as an analogous tool for serial cognitive testing for PD patients in clinical practice and cognitive trials.