Loss of phosphodiesterase 4 in Parkinson disease: Relevance to cognitive deficits.

OBJECTIVE

To assess in vivo the expression of phosphodiesterase 4 (PDE4) and its relevance to cognitive symptoms in patients with Parkinson disease (PD) using [C]rolipram PET.

METHODS

We studied 12 levodopa-treated patients with PD with no concurrent diagnosis of mild cognitive impairment or dementia. Their data were compared with those from 12 healthy controls. All participants underwent neuropsychiatric and cognitive assessment using the Cambridge Neuropsychological Test Automated Battery. Parametric images of [C]rolipram volume of distribution (V) values were determined with the Logan plot.

RESULTS

Patients with PD performed worse than healthy controls in cognitive examinations assessing psychomotor speed, episodic memory, and spatial working memory and executive function. Patients with PD showed reductions in [C]rolipram V compared to healthy controls, in the caudate (28%), thalamus (23%), hypothalamus (32%), and cortex (16%). Within thalamic subregions, [C]rolipram V values in patients with PD were decreased by 12%-32%, with most marked decreases observed in prefrontal and temporal thalamic nuclei, whereas motor nuclei were less affected. Within the cortex, [C]rolipram V values in patients with PD were decreased by 11%-20%, with most marked decreases observed in posterior dorsolateral frontal cortex, medial frontal cortex, and supplementary motor area, whereas orbitofrontal cortex was less affected. Worse performance in spatial working memory correlated with lower [C]rolipram V values in posterior dorsolateral frontal cortex, medial frontal cortex, supplementary motor area, precentral gyrus, caudate, and prefrontal thalamic nuclei.

CONCLUSIONS

Our findings demonstrate loss of PDE4 expression in the striato-thalamo-cortical circuit, which is associated with deficits of spatial working memory in patients with PD.