In addition to the different rates of loss, the scientists discovered that the various subject groups also exhibited different patterns of loss. In the Alzheimer's patients, widespread regions of gray and white matter were consistently wasted; only the primary motor and sensory cortices, brain stem and cerebellum were spared. The changes in the healthy controls were also somewhat diffuse. But in the four at-risk subjects, progressive atrophy was most pronounced in the posterior cingulate, the parietal lobe and, in particular, the medial temporal lobe.
The scientists warn that "some caution is needed in extrapolating results found in familial Alzheimer's disease to the more common sporadic Alzheimer's disease." Nevertheless, their findings accord well with other lines of study into the disease's histological changes (plaques, tangles, etc.), which probably precede any structural changes. "We have been able to show a presymptomatic phase of three years or more of increased rates of tissue loss," the authors explain. "The recognition of a presymptomatic phase, which extends beyond the medial temporal lobe, implies that structural changes might start earlier and are more widely distributed that previously appreciated."