Understanding the Connection Between Traumatic Brain Injury and Alzheimer's Disease: A Population-Based Medical Record Review Analysis

It seems true that some people, like boxers, are more likely to develop Parkinson's disease after being repeatedly knocked out or taking punches to the head. But not all boxers appear to have that risk. And it is well known that traumatic brain injury (TBI) can cause thinking problems right after the injury. Some research has shown that a history of TBI can increase the risk for developing thinking problems (like dementia) later in life that they otherwise would not have developed, while other studies have shown no such risk. The reason for this disagreement most likely relates to the many different ways researchers have defined TBI and other conditions, the varied populations chosen for study, and the many different groups used for comparison. People in military and civilian life are at greatest risk for milder TBI, and it is common that this group is not represented in this research. The best and most accurate way to find out whether having a TBI increases risk for developing conditions like Alzheimer's disease, Parkinson's disease, or other age-related thinking problems, is to identify a large group of individuals within a defined population (for instance, in an entire county) who we know had a TBI by looking in their medical record with their consent. That allows us to collect a sample of individuals that represents the population of that county (all ages and both sexes), determine how severe the TBI was (mild, moderate, or severe), and count how many injuries an individual had. When a group of individuals with TBI that represents the population is identified, each of those individuals can be matched to another member of the population who are like the individual with TBI (same age and sex), but who did not have a TBI as determined by reviewing their medical record with their consent. By following both groups over time, and reviewing their medical records to determine which people in either group develop Alzheimer's disease or one of the other related conditions, it can be determined with confidence whether TBI increases the risk for developing one of those conditions. Research that requires reviewing thousands of medical records is extremely difficult and time-consuming. The Mayo Clinic established the Rochester Epidemiology Project in the mid-1960s, linking all the medical records of everyone in the population of Olmsted County in Minnesota who consents, and has been doing exactly this sort of research since then. The scientists involved in this application have over a decade of experience specifically studying TBI and Alzheimer's disease and related conditions in the entire population of Olmsted County. In this way, the Mayo Clinic provides the unique resources and expertise that is required to determine whether a history of TBI adds risk for developing Alzheimer's disease or a related condition. From extensive clinical and research experience with individuals with TBI and Alzheimer's disease, we expect to find no consistent connection between them overall. But because we anticipate having a large sample of almost 2500 individuals with TBI of all severities, we are likely to find that individuals with certain characteristics -- such as those who have many injuries or injuries at a certain age or of a certain severity -- might show an increased risk for developing Alzheimer's disease or a related condition. If so, we could contact those individuals for additional clinical evaluation and potentially be able to identify those at the highest risk earlier in life.