The core criterion for Parkinson's disease dementia (PDD) is the impairment in activities of daily living (ADL) function primarily caused by cognitive, not motor symptoms. There is evidence to assume that mild ADL impairments in mild cognitive impairment (PD‐MCI) characterize those patients at high risk for dementia. Data of 216 Parkinson's disease (PD) patients assessed with comprehensive motor and neuropsychological assessments were analysed. Based on linear regression models, subscores of the Functional Activities Questionnaire (FAQ) primarily reflecting patients’ global cognitive status (FAQC) or PD‐related motor severity (FAQM) were developed. A quotient (FAQQ) of both scores was calculated, with values >1 indicating more cognitive‐ compared to motor‐driven ADL impairment. Both FAQC and FAQM scores were higher in PD‐MCI than cognitively normal (PD‐CN) patients, indicating more severe cognitive‐ and motor‐driven ADL impairments in this group. One third (31.6%) of the PD‐MCI group had a FAQQ score >1, which was significantly different from patients with PD‐CN (p = .02). PD‐MCI patients with an FAQQ score >1 were more impaired on tests assessing attention (p = .019) and language (p = .033) compared to PD‐MCI patients with lower FAQQ values. The differentiation between cognitive‐ and motor‐driven ADL is important, as the loss of functional capacity is the defining factor for a diagnosis of PDD. We were able to differentiate the cognitive‐driven from the motor‐driven ADL impairments for the FAQ. PD‐MCI patients with more cognitive‐ compared to motor‐driven ADL impairments may pose a risk group for conversion to PDD and can be targeted for early treatments.

Objectives:Parkinson’s disease (PD) patients with mild cognitive impairment (PD-MCI) have an increased risk of developing dementia (PDD). As activities of daily living (ADL) impairment is mandatory for the diagnosis of PDD, assessing early signs of instrumental ADL (iADL) dysfunction, especially in PD-MCI, is essential. In PD, self- and caregiver-reported iADL performance is often confounded by motor dysfunction and mood. Objective and time-efficient performance-based measurements are needed to screen for cognitive-related iADL dysfunction. We evaluated the Erlangen Test of Activities of Daily Living in Mild Dementia and Mild Cognitive Impairment (ETAM) in PD and determined its value for characterizing a subgroup of PD-MCI patients with mild performance-based iADL impairment.Methods:Twenty-one cognitively normal PD patients (PD-NC), 24 PD-MCI patients, and 18 healthy controls (HC) were analyzed. Assessments included the ETAM, a comprehensive neuropsychological test battery, iADL, mood, and motor measurements.Results:PD-MCI patients scored significantly lower on the ETAM total score compared to PD-NC patients (p = .002), whereas HC and PD-NC patients did not statistically differ. No HC scored lower than 27 points (diagnostic cutoff for mild iADL impairment); only PD-MCI patients scored below this cutoff (29.2%) suggesting the ETAM is able to characterize a PD-MCI subgroup with early iADL impairment. PD-MCI patients below the cutoff were more impaired in the attention domain (p = .04).Conclusions:The ETAM is a potentially valuable clinical assessment, able to detect first signs of iADL dysfunction in PD-MCI. Further studies in larger cohorts are needed to evaluate the prognostic ability for predicting PDD.