Globus pallidus dopamine and Parkinson motor subtypes - Clinical and brain biochemical correlation

Background: Patients with Parkinson disease (PD) may be akinetic/rigid, be tremor dominant, or have comparable severity of these motor symptoms (classic). The pathophysiologic basis of different PD phenotypes is unknown. This study assessed pallidal and striatal dopamine level patterns in different motor subgroups of PD and normal control brains. Methods: Globus pallidus and striatum dopamine (DA) levels were measured with high performance liquid chromatography in eight autopsy confirmed PD and five control frozen brains. Results: DA levels in the external globus pallidus (GPe) of normal brains were nearly six times greater than in the internal pallidum (GPi). In PD, the mean loss of DA was marked (-82%) in GPe and moderate (-51%) in GPi. DA loss of variable degree was seen in different subdivisions of GPe and GPi in PD; however, DA levels were near normal in the ventral (rostral and caudal) GPi of PD cases with prominent tremor. There was marked loss of DA (-89%) in the caudate and severe loss (-98.4%) in the putamen in PD. The pattern of pallidal DA loss did not match the putaminal DA loss. Conclusion: There is sufficient loss of dopamine (DA) in external globus pallidus and the internal globus pallidum (GPi) as may contribute to the motor manifestations of Parkinson disease (PD). The possible functional disequilibrium between GABAergic and DAergic influences in favor of DA in the caudoventral parts of the GPi may contribute to resting tremor in tremor dominant and classic PD cases.