Measuring functional impact of cognitive impairment: validation of the Parkinson's disease cognitive functional rating scale.

BACKGROUND: Little is known on the impact of cognitive impairment on instrumental activities of daily living (IADL) in pre-dementia stages of Parkinson's disease (PD).
OBJECTIVE: To investigate the clinimetric properties, applicability and responsiveness of a brief questionnaire (twelve-item; maximum score = 24) for rating functional abnormalities associated to cognitive impairment in non-demented PD patients (ND-PD).
METHODS: Two studies were carried-out: (1) a clinimetric study validated the Parkinson's Disease-Cognitive Functional Rating Scale (PD-CFRS) against the Older Americans Resource Survey (OARS-IADL) in 53 ND-PD patients and 53 matched controls; (2) A prospective multicenter 6-month responsiveness study involving 120 ND-PD patients explored sensitivity to change.
RESULTS: In the clinimetric study the PD-CFRS showed intermediate concurrent validity (ICC = 0.50), high test-retest (ICC = 0.82), inter-rater reliability (ICC = 0.80) and internal consistency (Cronbach's α = 0.79), and higher coefficient of variation to detect dysfunction in ND-PD patients (PD-CFRS 86.6% vs. OARS-IADL 8.1%). There was a strong relationship between the PD-CFRS and the global cognitive status determined with the PD-Cognitive Rating Scale (r = -0.72, p < 0.0001). The responsiveness study recruited 63 patients with normal cognition and 57 with mild cognitive impairment (MCI); an increase of 2 points in the PD-CFRS after 6 months was associated with a clinically significant worsening of the cognitive functional status. According to a discriminant analysis a PD-CFRS cut-off score of ≥3 was found to be optimal for detecting functional impairment in PD-MCI patients.
CONCLUSIONS: Cognitive impairment exerts measurable impact on IADL in ND-PD patients that can be reliable measured with the PD-CFRS, a PD-validated instrument that can be useful in clinical and research settings.