Longitudinal study on cognition in degenerative parkinsonisms

Executive function impairment is frequent in Parkinson's disease (PD), striato-nigral-degeneration-type multisystem atrophy (SND) and progressive supranuclear palsy (PSP); sometimes frank dementia is also present. However the progression of cognitive decline has not been delineated in these diseases. To clarify the progression of cognitive impairment in PD, SND and PSP patients and elucidate differences between the diseases, we compared 23 SND and 21 PSP patients, referred consecutively, and 18 PD patients matched for severity of parkinsonism on a comprehensive battery of cognitive tests and motor invalidity scales at baseline and again a mean of 21 months later (range 18-24 months). Patients with PSP performed worse than PD and SND patients in most cognitive tests, while PD and SND patients performed similarly, both at first and second evaluations. Twelve PD (66.6%), 14 SND (60.8%) and 11 PSP (52.4%) patients were re-tested; dropouts refused, had died or were too disabled. The PD group did not deteriorate in any cognitive measure, while SND patients deteriorated significantly in verbal fluency, attention and visuospatial tests. PSP patients worsened significantly in MMSE and in tests examining attention, executive functions and visuospatial organisation. Three PSP patients (14.3%) were demented at first evaluation and six (54.5%) at second evaluation; no PD or SND patients were demented (DSM IV criteria). The faster and more pervasive cognitive decline in PSP patients is probably related to conspicuous frontal deafferentation associated with direct premotor and prefrontal involvement, and dysfunction of the midbrain ascending activating system.