Histopathologic correlates of white matter changes on MRI in Alzheimer's disease and normal aging

We investigated the histopathologic correlates of white matter changes in Alzheimer's disease (AD) patients (n = 6) and controls (n = 9) using postmortem MRI. White matter changes were rated on a 0 to 3 scale in 51 regions. Histopathologically, we subjectively rated the loss of myelinated axons in the deep and periventricular white matter, denudation of the ventricular ependyma, gliosis, width of the perivascular spaces, and leptomeningeal congophilic angiopathy; we measured structural changes in the walls of the blood vessels in the white matter in micrometers. The AD brains displayed significantly more white matter hyperintensities on MRI than controls. Histopathologically, the denudation of the ventricular ependyma and the gliosis were significantly more severe in AD than in controls, and there was a trend toward more loss of myelinated axons in the deep white matter in the AD brains (p = 0.07). The MRI abnormalities correlated with the loss of myelinated axons in the deep white matter (r' = 0.37; p < 0.01) and with the denudation of the ventricular lining (r' = 0.54; p < 0.01). We could not find any evidence for arteriolosclerosis, but the mean thickness of the adventitia of the arteries of the deep white matter in AD almost doubled the value in control brains (p = 0.0009). We conclude that white matter abnormalities in AD patients and controls consist of loss of myelinated axons, probably caused by arterial changes and breakdown of the ventricular lining. Since imaging/histopathologic correlation was similar in AD patients and controls, these changes probably represent some form of accelerated aging.