Screening for cognitive impairment in Parkinson's disease--which marker relates to disease severity?

The frequency and pattern of cognitive deficits in Parkinson's disease (PD) is under discussion. We assessed 157 consecutive subjects with PD (66.4 +/- 8.9 years (mean +/- standard deviation); average duration of disease 3.5 +/- 1.3 years; average Hoehn and Yahr stage 2.4 +/- 0.9) diagnosed in centers specialized for the diagnosis and treatment of PD with brief tests for memory (Memory Impairment Screen), attention (Letter Sorting Test) and semantic fluency (category animals). Impaired memory was observed in about one half of the subjects regardless of severity of disease as assessed by staging according to Hoehn and Yahr. With greater severity, free recall was impaired and subjects required the cues to recall the items. Performance in the Letter Sorting Test and the semantic fluency task declined with increasing Hoehn and Yahr stage, also. We conclude that cognitive deficits are frequent in PD. Further analyses reveal that even in selected screening tests (e.g. semantic fluency) a significant impairment with increasing disease severity (Hoehn and Yahr stage) as opposed to disease duration alone can be demonstrated.