Striatal dopaminergic correlates of the Montreal Cognitive Assessment test and the Mini Mental State Exam in Parkinson disease: A [11C]-DTBZ PET study

2003 Objectives Cognitive impairment is common in Parkinson disease (PD), especially in more advanced stages of the disease. A common screening method for cognitive assessment is the Mini Mental State Exam (MMSE). Compared to the MMSE, the Montreal Cognitive Assessment test (MoCA) is supposedly more sensitive in detecting so-called Mild Cognitive Impairment (MCI). It is unclear, however, how both tests relate to striatal dopaminergic denervation, the pathophysiological hallmark of PD. Methods 26 PD patients (1F/25M; 67.0±7.4 (50-84) years; 6.1±3.2 (1-14) years motor disease duration; Hoehn and Yahr (HY HY HY H&Y 3: N=7) underwent striatal [11C]-DTBZ PET imaging for assessment of striatal dopaminergic nerve terminal integrity. All patients were simultaneously enrolled in one study that used the MMSE and another study that used the MoCA for cognitive assessment.. Striatal [11C]-DTBZ Distribution Volume Ratio (DVR) was calculated using the non-invasive Logan plot approach with the neocortex as the reference region. Results The average MMSE score was 28.5±1.9 (22-30) and the average MoCA score was 24.8±2.3 (19-29). Neither motor disease duration nor Hoehn and Yahr stage correlated significantly with either the MMSE score or MoCA score. Higher MoCA scores were associated with higher striatal [11C]-DTBZ DVR (ρ=0.410, p=0.037); MMSE did not correlate with striatal [11C]-DTBZ DVR (ρ=0.0, ns). Conclusions Decreased MoCA but not MMSE scores, are associated with decreased nigrostriatal nerve terminal integrity. Whereas it is possible that the MoCA may better reflect subcortical than cortical cognitive changes, it is also possible that the MoCA score may be affected more by motor impairment associated with striatal dopaminergic denervation while the MMSE is not. Research Support NIH P01 NS015655 & RO1 NS070856 and Department of Veterans Affair