Potential usefulness of signal intensity of cerebral gyri on quantitative susceptibility mapping for discriminating corticobasal degeneration from progressive supranuclear palsy and Parkinson's disease

The typical MRI findings in corticobasal degeneration (CBD), which have been described in previous reports, may be non-specific. We evaluated cerebral gyri (CG) using quantitative susceptibility mapping (QSM) images of patients with CBD, progressive supranuclear palsy (PSP), and Parkinson's disease (PD) to determine the possibility of discriminating them on an individual basis. After reviewing the normal appearances on QSM on 16 healthy subjects, two radiologists assessed abnormal findings from 12 CBD, 14 PSP, and 30 PD patients. For conventional MRI, two radiologists independently reviewed typical CBD findings that have been previously reported. We also investigated three autopsy cases including one each of CBD, PSP, and PD to reveal the histopathological basis of MRI findings. CBD-specific findings included three layers; a higher susceptibility layer in superficial GM, a lower susceptibility layer, and a higher susceptibility layer in corticomedullary junction, with frequencies of 83% (10/12) in CBD, 21% (3/14) in PSP, and 0% (0/30) in PD patients. The typical CBD findings on conventional MRI were observed in only 42% (5/12) of CBD patients. Ferritin-positive microglia accumulated in the superficial gray matter (third cortical layer) and corticomedullary junction in CBD patients. The CG findings on QSM images may be more useful than those on conventional MRI for discriminating CBD from PD on an individual basis. Based on postmortem pathological data, cortical QSM hyperintensity might be an expression of ferritin-positive microglia.