How do cognitive and axial motor signs correlate in Parkinson's disease? A 6-year prospective study.

Impairment of Parkinson's disease (PD) axial motor signs (AMS) has been described as a risk factor for dementia. Executive dysfunction is an important feature in recently proposed clinical diagnostic criteria for PD dementia. To clarify the relationship between AMS progression and executive cognitive performance, we conducted a 6-year prospective study in PD patients without AMS impairment at baseline. A hospital-based cohort of PD patients (n = 24) without dementia, in the initial motor stage (Hoehn-Yahr < or = 2), and matched controls (n = 20) were followed prospectively over a 6-year period. Neuropsychological tests were performed in both groups, and motor function (including AMS: speech, gait, postural instability) was evaluated in the PD group. The PD group had a significantly higher decline in neuropsychological test scores than did the controls. Most of the neuropsychological and motor decline occurred in the last 4 years. In UPDRS III, progression of AMS and especially speech were the most important motor variables related to dementia. There was a correlation between speech impairment progression and declines in MMSE (r = -0.598, p = 0.002), Clock Drawing (r = -0.671, p < 0.001), Semantic Verbal Fluency (r = -0.435, p = 0.034), Alternating Sequences (r = 0.497, p = 0.014), and Raven's Coloured Progressive Matrices (r = -0.735, p < 0.001). PD patients with higher speech impairment progression showed more rapid declines in some neuropsychological tests. Further studies are needed to clarify the different roles of speech, gait and postural instability on the initial phases of cognitive dysfunction.