When former athletes with severe brain damage experience cognitive issues, doctors have been quick to blame Alzheimer’s disease in recent years. Notably, however, autopsies later revealed many of those patients actually had no Alzheimer’s at all. They had chronic traumatic encephalopathy (CTE). Researchers estimate CTE was misdiagnosed as dementia in 40% of advanced cases.
The finding comes from a Boston University study of 614 brain donors, including 366 with CTE. Among the 99 donors with advanced CTE who had been diagnosed with dementia during life, only 17% of physicians correctly identified CTE as the cause. The misdiagnosis rate points to a troubling gap in how doctors recognize this disease.
The study, published in Alzheimer’s & Dementia, also revealed differences by disease stage. Among donors with the most severe CTE (stage IV), roughly 8 in 10 had dementia before death, compared to just 16% of those without CTE. Those with stage IV were more than four times as likely to have had dementia. But surprisingly, early-stage CTE showed no connection to memory problems at all. Moreover, despite common assumptions, CTE severity had no link to depression or behavioral issues.
How the Disease Progresses
CTE comes in four stages as abnormal proteins gradually spread through the brain. Early stages (I and II) involve small pockets of damage in the frontal regions. By stage III, the proteins reach deeper memory areas. Stage IV means widespread damage across much of the brain.
Family members of the deceased athletes filled out detailed surveys about memory problems, personality changes, and daily functioning before death. Researchers combined these accounts with medical records to determine who had dementia.
The connection became clear at advanced stages. Stage IV donors scored about twice as high on cognitive difficulty assessments as people without CTE. They struggled far more with basic tasks like managing finances or remembering appointments.
Early-Stage CTE Shows No Symptoms
Early-stage CTE showed no link to dementia or memory problems at all. Stages I and II looked essentially the same as having no CTE.
“It is uncertain if low-stage CTE clinically manifests,” the authors wrote. This suggests the brain can initially tolerate small amounts of damage before symptoms appear.
This finding challenges assumptions that any amount of CTE causes problems. The brain appears capable of withstanding limited damage without triggering memory loss or personality changes. It’s only when the disease reaches advanced stages that dementia becomes highly likely.
Why the Confusion Happens
Both CTE and Alzheimer’s attack memory first, and patients show similar symptoms in the doctor’s office. Former football players often struggle to recall recent events and conversations, just like Alzheimer’s patients do. Without a brain scan that can detect CTE, doctors often assume the more common diagnosis.
Vascular dementia accounted for another 10% of misdiagnoses, and 38% of doctors labeled the condition as “dementia unspecified or unknown.” Among all the physicians who diagnosed dementia in patients with advanced CTE, only 17% correctly identified CTE as the cause.
This raises a troubling possibility: some former athletes with dementia may be told they have Alzheimer’s when the real cause is CTE. The study can’t put a number on how often this happens among living people, but the mismatch researchers found in autopsy cases suggests it could be more common than anyone realizes.
Severe CTE Strongly Linked to Dementia
CTE severity had no connection to depression, anxiety, or impulsiveness in this study. That finding contradicts popular assumptions that CTE directly causes the mood and behavior problems many former athletes experience.
More likely, those symptoms come from multiple sources. Brain imaging often shows damage to white matter (the brain’s wiring) and blood vessels in former players. Chronic pain, sleep problems, and past substance use probably contribute too. CTE might be one factor among many, rather than the sole culprit for behavioral issues.
Some former athletes struggle with anger, depression, or impulsive behavior for years before memory problems appear. This study suggests those early struggles may not come from CTE itself, but from the accumulated toll of repeated hits, injuries, and the lifestyle that often accompanies professional sports.
Even after researchers accounted for blood vessel damage and other brain issues, the link between severe CTE and dementia held firm. Mood symptoms remained unconnected to disease stage.
What This Means for Athletes
The study focused almost entirely on male athletes, with 80% having played American football. Most with severe CTE had played at the college or professional level for many years. Those with the worst brain damage had typically started playing young and continued for decades.
The good news, if any exists here, is that mild CTE may not cause symptoms. The brain appears capable of withstanding limited damage without triggering memory loss or personality changes. The bad news is that once CTE reaches advanced stages, dementia becomes highly likely.
Researchers also found that age matters less than disease severity. Even when they looked specifically at donors 52 and older to control for natural aging, advanced CTE still carried the same elevated dementia risk. The disease itself, not just getting older, drives cognitive decline.
The Challenge of CTE Diagnosis
Right now, doctors cannot diagnose CTE in living people. Brain tissue must be examined under a microscope after death to spot the telltale protein deposits around blood vessels. This leaves athletes and their families in limbo, wondering whether symptoms stem from CTE or something else entirely.
