Causes

Repetitive head trauma is likely the cause of CTE. Football and ice hockey players, as well as military personnel serving in war zones, have been the focus of most CTE studies, though other sports and factors such as physical abuse also can lead to repetitive head injuries.

However, not all athletes and not everyone who experiences repeated concussions, including military personnel, go on to develop CTE. Some studies have shown no increased incidence of CTE in people exposed to repeated head injuries.

In brains with CTE, researchers have found that there is a buildup of a protein called tau around the blood vessels. Tau buildup in CTE is different from accumulations of tau found in Alzheimer's disease and other forms of dementia. CTE is thought to cause areas of the brain to waste away (atrophy). Injuries to the sections of nerve cells that conduct electrical impulses affect communication between cells.

It's possible that people with CTE may show signs of another neurodegenerative disease, including Alzheimer's disease, amyotrophic lateral sclerosis (ALS) — also known as Lou Gehrig's disease — Parkinson's disease or frontotemporal lobar degeneration (frontotemporal dementia).