Assessing the utility of the Movement Disorder Society Task Force Level 1 diagnostic criteria for mild cognitive impairment in Parkinson's disease

• Substantial differences in PD-MCI frequencies with different sets of MDS criteria.
• Refinement of the MDS criteria is needed to standardize PD-MCI diagnosis.
• Characterization of PD-MCI should relate to decline from premorbid intellect.
• Clarification of an optimal cut-off point for characterizing MCI is needed.

BackgroundUsing the Movement Disorder Society (MDS) Task Force Level 1 criteria, this study examined the classification of mild cognitive impairment in Parkinson's Disease (PD-MCI) derived from a range of cut-off scores that have previously been suggested by the MDS Task Force. Furthermore, differences in PD-MCI frequencies were examined when comparing performance on current neuropsychological testing to the normative sample, as opposed to decline from premorbid functioning, as evidence of cognitive impairment.MethodTwo hundred and thirty-four non-demented PD patients underwent neurological and neuropsychological assessment at the Parkinson's Disease Research Clinic at the Brain and Mind Research Institute, University of Sydney.ResultsWhen cognitive impairment was defined as 1SD and 1.5SD below premorbid intellect, 109 patients (47%) and 76 (32%) patients met criteria for PD-MCI respectively. This proportion dropped considerably to 50 patients (21%) with a 2SD cut-off score. However, when calculating impairment based on comparisons with normative data, only 68 patients (29%) and 41 patients (18%) met PD-MCI criteria when a cut-off score of 1 and 1.5SD was employed. This proportion dropped to just 22 patients (9%) with a 2SD cut-off score.ConclusionResults from the present study suggest that the MDS PD-MCI criteria may be too broad, as substantial differences in frequencies of PD-MCI were observed with the application of differing criteria. We propose that a 1.5SD cut-off score below premorbid functioning may provide greater utility in characterizing PD-MCI than a 1.5SD cut-off below normative data, which has been widely applied in previous studies examining the MDS PD-MCI criteria.