Intact presupplementary motor area function in early, untreated Parkinson's disease

Although motor symptoms of Parkinson's disease (PD) are initially responsive to dopamine replacement therapy, nonresponsive features develop over time, suggesting that impaired dopaminergic function alone may not be wholly responsible for all the motor features of the disease. Previous studies suggest impaired function in the presupplementary motor area (pre-SMA) in PD. Our objective was to determine whether pre-SMA abnormalities are present in untreated patients with early disease. We measured N-acetyl aspartate (NAA)/creatine (Cr) and choline (Cho)/Cr ratios in pre-SMA in 26 untreated patients with early PD (disease duration 3.0 +/- 2.0 yr) and 15 control subjects with single voxel magnetic resonance spectroscopy. Neither NAA/Cr nor Cho/Cr ratios differed significantly between groups. These observations suggest that, although pre-SMA function is impaired in moderately advanced PD, it is relatively spared in early disease. We suggest that pre-SMA dysfunction is in part responsible for the dopamine nonresponsive features associated with disease progression.