Separating cognitive and motor contributions to iADL difficulties in Parkinson's disease

Mild Cognitive Impairment (MCI) and dementia are distinguished by whether cognitive deficits interfere with independent performance of instrumental activities of daily living (iADLs). In Parkinson's disease (PD) this distinction is challenging due to the combined impact of motor and cognitive symptoms on autonomy. To address this, we examine two methods aimed at isolating these contributions using the Functional Activities Questionnaire (FAQ): (1) a modified scoring method that classifies items as motor or cognitive to compute a ratio of the two contributors (FAQ_Q), and (2) a novel, extended FAQ that captures patients' and care-partners' perspective to elucidate the cognitive burden experienced.

We conducted a retrospective chart review of PD patients (n = 283) prior to Deep Brain Stimulation. We extracted ratings from the standardized and extended FAQ, cognitive diagnoses [PD-MCI: n = 164; cognitively normal (PD-CN) n = 119], neuropsychological test scores, and demographic and clinical variables. We examined the degree to which respondents attributed iADL difficulties to motor and cognitive symptoms, and whether these ratings matched the modified scoring method's categorization. To validate this scoring method in our sample, we examined each standardized FAQ item's relationship with measures of motor symptoms (UPDRS-III) and global cognition (DRS-II). Lastly, we derived a Reported Cognitive Burden (RCB) score from the extended FAQ and examined how it, and the FAQ_Q, relate to cognitive status (PD-CN vs. PD-MCI) and performance on neuropsychological tests.

Patients and care-partners reported that iADLs were more limited by motor symptoms, even for items categorized as "cognitive." Regression models did not achieve the same item classification as prior research using the modified scoring method. The RCB, but not the FAQ_Q, was higher in PD-MCI than PD-CN and related to performance in attention and executive domains regardless of who provided the ratings.

Patient's and care-partner's appraisal of the source of iADL difficulties was inconsistent with previous categorization of FAQ items in patients with more advanced PD. Our novel RCB offers a sensitive means of detecting mild functional changes related to cognition even in the presence of highly disabling motor symptoms, and may aid in establishing cognitive diagnoses in PD and other neurodegenerative disorders.