A new article on cerebral microbleeds in memory clinic patients was published in the May 9 issue of Neurology. Microbleeds are the small hemorrhages that doctors could see signs of on the MRI of my father's brain. Thes microbleeds happen when the blood vessel walls in the brain thicken, harden and then crack, allowing blood to seep into the brain. This can be caused by high blood pressure or by deposits of a protein called amyloid on the vessel walls (cerebral amyloid angiopathy).
The Neurology article describes how researchers from the Department of Neurology/Alzheimer Center at the Vrije Universiteit (VU) Medical Center in Amsterdam looked for cerebral microbleeds in 772 memory clinic patients. They found microbleeds in 65% of vascular dementia patients (whose dementia is caused by problems with blood supply to the brain), 18% of Alzheimer's disease patients and 20% of patients diagnosed with mild cognitive impairment. While these percentages are lower than those of hemorrhagic stroke patients (estimated at 68% in one study), they are higher than the percentages found in the general population. For example, as part of the Framingham study in the US, researchers found microbleeds in 4.7% of 472 participants with a mean age of 64 years, only two years younger than the mean age of the Dutch memory clinic patients.
The VU scientists' findings raise some questions about the relationship of microbleeds and vascular disease to Alzheimer's. Currently, vascular dementia and Alzheimer's are viewed as separate conditions. But some researchers wonder whether vascular disease causes or contributes directly to Alzheimer's.
For an expert opinion on these issues, I checked in with Dr. Philip Scheltens, Professor of Cognitive Neurology, Director of the Alzheimer Center at the Vrije Universiteit Medical Center and co-author of the new study. His study concludes that the relatively high proportion of microbleeds in Alzheimer's disease and mild cognitive patients "provides further evidence for the involvement of vascular factors in neurodegenerative disease such as Alzheimer disease."
Dr. Philip Scheltens
I asked Professor Scheltens whether he thinks microbleeds might actually cause or contribute to Alzheimer's. "I think they are yet another phenomenon that occurs alongside Alzheimer's," he says, "and certainly do not cause it but may precipitate the clinical picture."
Could microbleeds cause dementia independent of Alzheimer's? "That we don't know yet," Professor Scheltens says, noting that there are not enough large studies on this topic to come to a firm conclusion. "My view is that AD is a clinical label to which many pathologies can contribute; there are pure cases and cases where degenerative and vascular pathology go together and one may influence the other."
I'm waiting for an analysis of Dad's tissue that I hope will provide more clues as to what caused his dementia, and whether he had cerebral amyloid angiopathy and/or Alzheimer's. In the meantime, studies like Professor Scheltens' are providing more clues about the relationships among these conditions and diseases. That may help researchers better understand the causes of dementia and eventually lead to the development of more effective treatments.