Structural changes of the substantia nigra in Parkinson's disease as revealed by MR imaging

Abstract

Background and purpose: The possibility of using MR imaging as a sensitive marker of the structural changes in Parkinson's disease has been a long-sought goal. We describe a new method for imaging and quantifying the morphologic changes of the substantia nigra in Parkinson's disease and compare radiologic findings with clinical evaluation.

Methods: Using a combination of two MR imaging inversion-recovery pulse sequences, the substantia nigra was imaged in six patients with Parkinson's disease and six age-related control participants. A radiologic index was defined and used to quantify the signal changes that were observed in the patients. The radiologic index was compared with clinical scores obtained from the Unified Parkinson's Disease Rating Scale.

Results: The images showed loss of signal in a lateral-to-medial gradient in cases of Parkinson's disease, corresponding to the known neuropathologic pattern of degeneration. The radiologic index was highly correlated with the Unified Parkinson's Disease Rating Scale score, and there was no overlap in radiologic indices between the patient and the control groups (P < .00005).

Conclusion: This study suggests that MR imaging is sensitive to structural changes in even the earliest cases of Parkinson's disease, thereby indicating the potential for detecting presymptomatic disease. Furthermore, a radiologic measure has been defined that correlates with the conventional clinical measure of disease severity. Therefore, MR imaging could prove to be a sensitive biological marker for objective staging of the disease.

fig 1.

Upper row displays an example of axial WMS and GMS MR acquisition images of the mesencephalon in a control participant. The cerebral peduncle (second row, left) extracted from the WMS midbrain image serves as a template to extract the GMS image of the cerebral peduncle shown on the right. The SN_C is seen as a bright arch in the peduncular WMS image, whereas it appears as a dark band in the corresponding GMS image. Note also the substantia nigra pars reticulata (SN_R) reaching across the crus cerebri toward the SN_C. The ratio image (WMS/GMS) of the two images in the second row yields the color-coded ratio image displayed on the bottom. All black and white images are shown using a standard display of 256 gray levels. The color image uses a 256-pseudocolor lookup table.fig 2. Ratio images of the cerebral peduncle displayed in pseudocolors show the morphologic characteristics of the SN_C in two control participants (C1 and C2) and the structural changes in two patients with Parkinson's disease (P1 and P2). The substantia nigra pars reticulata (SN_R) is indicated for participant C1. Notice that the SN_C in control participants reaches out toward the peduncular edge in the upper section, taking on the form of an arch. In the images of patient P1, who has Parkinson's disease, thinning and loss of signal can be seen in the lateral segment of the SN_C in the upper section. The lower section shows islands of cell loss on both sides of the SN_C. Note the considerable thinning and loss of signal in both upper and lower sections of the images of patient P2, who has late-stage Parkinson's disease. Left and right sides show two rims of preserved signal

fig 3.

Radiologic indices are displayed for the six control participants and the six patients with Parkinson's disease. There is no overlap between the groups, which are distinct by Student's t test (P < .00005). The error bars represent one SD.fig 4. Unified Parkinson's Disease Rating Scale scores for the six patients ranging from 12 to 71 are plotted versus radiologic indices. A linear regression analysis was conducted, yielding a linear correlation coefficient of r = 0.99