Global versus factor-related impression of severity in Parkinson's disease: a new clinimetric index (CISI-PD).

In Parkinson's disease (PD), the Clinical Global Impression of Severity (CGIS) is often used as an additional outcome in clinical trials. It is hypothesized that this measure summarizes clinical assessment and is mainly influenced by the rating of four domains, namely, motor signs, disability, motor complications, and cognitive impairment. Ratings of these four factors were combined to form a new Clinical Impression of Severity Index for Parkinson's Disease (CISI-PD). A sample of 150 PD patients was evaluated using the following scales: Hoehn and Yahr staging, Schwab and England scale, Unified Parkinson's Disease Rating Scale, Scales for Outcomes in Parkinson's Disease-Motor Scale, CGIS, and CISI-PD. The results show that the CGIS is closely related to the above-mentioned measures (r=0.49-0.89). CISI-PD correlation with these scales was very similar (r=0.55-0.91), to the extent that the difference between corresponding coefficients was systematically less than 0.10. A multiple regression model showed that 92% of the CIGS variance was explained by the four CISI-PD items. Finally, the CISI-PD displayed adequate psychometric properties, with satisfactory internal consistency (alpha=0.90) and convergent (r>0.75) and known-groups validity. The CISI-PD is a valid and reliable measure that expands the information obtained via the CGIS.