The recently proposed Movement Disorder Society (MDS) Task Force diagnostic criteria for mild cognitive impairment in Parkinson’s disease (PD-MCI) represent a first step towards a uniform definition of PD-MCI across multiple clinical and research settings. Several questions regarding specific criteria, however, remain unanswered including optimal cutoff scores by which to define impairment on neuropsychological tests.

Seventy-six non-demented PD patients underwent comprehensive neuropsychological assessment and were classified as PD-MCI or PD with normal cognition (PD-NC). Concordance of PD-MCI diagnosis by MDS Task Force Level II criteria (comprehensive assessment), using a range of standard deviation (SD) cutoff scores, was compared to our consensus diagnosis of PD-MCI or PD-NC. Sensitivity, specificity, positive and negative predictive values were examined for each cutoff score. PD-MCI subtype classification and distribution of cognitive domains impaired were evaluated.

Concordance for PD-MCI diagnosis was greatest for defining impairment on neuropsychological tests using a 2 SD cutoff score below appropriate norms. This cutoff also provided the best discriminatory properties for separating PD-MCI from PD-NC, compared to other cutoff scores. With the MDS PD-MCI criteria, multiple domain impairment was more frequent than single domain impairment, with predominant executive function, memory, and visuospatial function deficits.

Application of the MDS Task Force PD-MCI Level II diagnostic criteria demonstrates good sensitivity and specificity at a 2 SD cutoff score. The predominance of multiple domain impairment in PD-MCI with the Level II criteria suggests not only influences of testing abnormality requirements, but also the widespread nature of cognitive deficits within PD-MCI.