MRI can detect nigral volume loss in patients with Parkinson's disease: evidence from a meta-analysis.

BACKGROUND Parkinson's disease (PD) involves the degeneration of dopaminergic neurons in substantia nigra (SN) compacta. However, it is still a contentious issue whether magnetic resonance imaging (MRI) can detect the nigral volume loss in PD patients. OBJECTIVE We synthesized the results of published research on SN volumetry using a meta-analysis method in order to clarify this issue. METHODS A comprehensive literature search yielded 8 eligible studies. Nigral size was expressed as the standardized mean difference (SMD) between normal controls and PD patients. In addition, subgroup analysis was performed in order to identify the best condition for nigral volumetry. The proportion of variation due to heterogeneity was computed and expressed as I2. RESULTS Eight studies involved 172 normal control and 193 PD patients. The overall effect indicated that nigral volume in PD was significantly smaller than normal controls with homogeneous studies (SMD = -0.65, P < 0.0001; I2 = 47%). Maximum of subgroup effect was observed in 'volumetry' among three approaches ('thickness': SMD = -0.35, P = 0.18, I2 = not available; 'area': SMD = -0.39, P = 0.14, I2 = 0%; 'volumetry': SMD = -0.82, P = 0.0006, I2 = 56%). The approach including T1-weighted images (T1WI) showed larger effect ('with T1WI': SMD = -1.11, P < 0.00001, I2 = 36%; 'without T1WI': SMD = -0.32, P = 0.04, I2 = 0%). CONCLUSIONS These findings suggest that volumetry based on T1WI could be the most sensitive option to identify nigral volume loss in PD patients.