An experience of three or more concussions is associated with a fivefold greater chance of developing Alzheimers disease earlier and a threefold greater chance of developing memory deficits.Chronic traumatic encephalopathy, or "CTE", is an example of the cumulative damage that can occur as the result of multiple concussions or less severe blows to the head. The condition was previously referred to as "dementia pugilistica", or "punch drunk" syndrome, as it was first noted in boxers. The disease can lead to cognitive and physical disablities such as parkinsonism, speech and memory problems, slowed mental processing, tremor, depression, and inappropriate behavior. It shares features with Alzheimers disease. Second-impact syndrome
Second-impact syndrome, in which the brain swells dangerously after a minor blow, may occur in very rare cases. The condition may develop in people who receive a second blow days or weeks after an initial concussion before its symptoms have gone away. No one is certain of the cause of this often fatal complication, but it is commonly thought that the swelling occurs because the brains arterioles lose the ability to regulate their diameter, causing a loss of control over cerebral blood flow. As the brain swells, intracranial pressure rapidly rises. The brain can herniate, and the brain stem can fail within five minutes. Except in boxing, all cases have occurred in athletes under age 20. Due to the very small number of documented cases, the diagnosis is controversial, and doubt exists about its validity.
Until the 17th century, a concussion was usually described by its clinical features, but after the invention of the microscope, more physicians began exploring underlying physical and structural mechanisms. However, the prevailing view in the 17th century was that the injury did not result from physical damage, and this view continued to be widely held throughout the 18th century. The word "concussion" was used at the time to describe the state of unconsciousness and other functional problems that resulted from the impact, rather than a physiological condition. In 1839, Guillaume Dupuytren described brain contusions, which involve many small hemorrhages, as contusio cerebri and showed the difference between unconsciousness associated with damage to the brain parenchyma and that due to concussion, without such injury. In 1941, animal experiments showed that no macroscopic damage occurs in concussion. Society and culture
Costs
Due to the lack of a consistent definition, the economic costs of mTBI are not known, but they are estimated to be very high. These high costs are due in part to the large percentage of hospital admissions for head injury that is due to mild head trauma, but indirect costs such as lost work time and early retirement account for the bulk of the costs. These direct and indirect costs cause the expense of mild brain trauma to rival that of moderate and severe head injuries.