There are more than 6 million people who are injured and about 200,000 who die in motor vehicle accidents annually around the world[106]. In the US, injury occurs in one in four people during a given year[106]. Injury is one of the leading causes of death over several age groups[106]. Injury from unintentional and intentional causes, for example, is the leading cause of death for children and adults between the ages of 1 and 44 years[106]. It has been estimated that there are 18 hospital discharges and 250 injury-related visits to hospital emergency department for every injury death[106].

Several population based studies favored an association between traumatic brain injury and subsequent Alzheimer’s disease[107,108]. For instance, a hazard ratio of 2.32 (confidence interval = 1.04 to 5.17) for moderate traumatic brain injury and a hazard ratio of 4.51 (confidence interval = 1.77 to 11.47) for severe head injury was observed in a historical cohort study of 548 World War II veterans[109]. A recent meta-analysis of case-control studies confirmed that men diagnosed with traumatic brain injury are at increased risk of developing Alzheimer’s disease[110]. 

Traumatic brain injury was identified based on the CDC surveillance guidelines[57]. Using ICD-9-CM methodology, it was calculated that there were 701 (0.009%) patients discharged with both traumatic brain injury and Alzheimer’s disease in 2001. Out of all discharges in 2001, the proportion of patients diagnosed with both traumatic brain injury and Alzheimer disease was highest among those aged 80-89 years old followed by those aged 70 – 79, followed by those 90 – 99 years old and finally those aged 60-69:

More than half of patients diagnosed with both traumatic brain injury and Alzheimer’s disease were among those aged 80-89 years old (54%) and about one third cases were among those aged 70-79 (30%):

There were more men than women diagnosed with both traumatic brain injury and Alzheimer’s disease were women (51% vs. 49%):

There were two more important findings. The proportion of patients diagnosed with both traumatic brain injury and Alzheimer’s disease was nearly twice as high as the proportion of patients diagnosed with Alzheimer’s disease and any other comorbidities (p < 0.001). In the adjusted (for age, gender, length of stay and primary source of payment) logistic regression analysis, patients diagnosed for traumatic brain injury were 1.82 times more likely to be diagnosed with Alzheimer’s disease (95% confidence interval 1.28 – 2.58).