LAUSR

Federico et al1 discuss the differences in normative values for global cognitive scales, including the Montreal Cognitive Assessment (MoCA) and the MiniMental State Examination (MMSE), across different populations, as well as sensitivity of these scales for detection of Parkinson's disease related mild cognitive impairment (PDMCI) at level I (Movement Disorder Society PDMCI Task Force diagnostic criteria). The issue of normative values is an important one, and caution should be exercised when interpreting results of cognitive testing in different patient populations. As discussed in our article,2 factors such as age, language, and education level often can affect results of cognitive testing. Moreover, the selection of the normative comparison group for cognitive testing plays an important role in interpreting cognitive testing results as well, and differences in “control” populations can lead to significantly differing normative values. Although some studies exclude participants as “healthy control” subjects only if they endorse subjective cognitive complaints, others apply more detailed and stricter criteria in which participants would be excluded as “healthy controls”: if they have other factors as well, for example, subjective complaints of memory loss, systemic illness, drug or alcohol use, or any abnormality on in depth neuropsychological assessment, neurologic examination, and brain imaging studies.3 These differences in definitions of “healthy control” populations thereby may lead to under or overestimation of PD MCI in the PD population.