Validation of new diagnostic criteria for fatigue in patients with Parkinson's disease

Background: Although disabling fatigue is common in Parkinson's disease (PD), available consensus-based diagnostic criteria have not yet been empirically validated. The aim of the study was to evaluate the clinimetric properties of the criteria. Methods: A sample of outpatients with PD was evaluated for demographic, clinical, behavioural, and cognitive features. Fatigue was diagnosed according to the new diagnostic criteria and was rated by means of the Parkinson Fatigue Scale (PFS) and Fatigue Severity Scale (FSS). Acceptability, concurrent and discriminant validity, and inter-rater reliability were evaluated with binary logistic regression analyses and Cohen's kappa (?). Results: Out of 241 included patients, 17 (7.1%) met the diagnostic criteria for PD-related fatigue. Eight out of nine symptoms described in section A of the diagnostic criteria occurred in >50% of patients with fatigue. Acceptability (missing data=0.8%) of the criteria was good, as well as their concurrent validity with the PFS (Odds Ratio=3.65) and FSS (Odds Ratio=3.63). The discriminant validity of fatigue criteria with other PD-related behavioural and cognitive features was good (Odds Ratio<1.68). The inter-rater reliability was excellent (?=0.92). Conclusions: This is the first study to test the clinimetric properties of case definition diagnostic criteria for PD-related fatigue. Our results suggest that current diagnostic criteria may be useful in both clinical practice and research. Future longitudinal studies should examine their long-term stability.