The damage in the brain of chronic traumatic encephalopathy begins showing symptoms many years after an athlete stops getting hit in the head — which could have been from professional football, hockey or boxing.

And this very delayed presentation of symptoms is what makes CTE so intriguing and mystifying.

Repeated hard strikes to the head during the athlete’s career is what leads to the symptoms of CTE, but not all athletes who suffer a lot of concussions or hits to the head develop this incurable condition.

CTE is progressive. It just keeps getting worse the longer the patient lives. And mysteriously, the cognitive symptoms aren’t present SOON after retirement from the sport — but many years after it.

Why do the symptoms of CTE take years after the head trauma to start showing?

“The short answer is we really do not know why,” explains neuropsychologist Kenneth Podell, PhD, co-director, Houston Methodist Concussion Center, concussion specialist for the Houston Texans and Houston Astros. I interviewed him for this article.

Another intriguing point to consider is that the symptoms of CTE keep on worsening, even though the brain is free of the insults caused by football, hockey or whatever the sport was that the athlete played.

Dr. Podell says this: “Cell death in the brain can take years to occur and must reach a critical level of damage or threshold before they clinically express themselves.”

The primary mechanism is the head trauma that’s suffered in football or hockey games or boxing matches.

And there is a secondary mechanism: the progression of changes in the brain — a progression that’s self-starting — that leads to worsening symptoms years later.

“The primary damage in CTE, at least one of the thoughts,” notes Dr. Podell, “is that the hits to the head and concussions damage the tau proteins that act like structure bridges or a lattice that supports the microtubules (the channels that transport information down the length of an axon or nerve cell) for communication with other nerve cells.”

Dr. Podell then adds, “Without the proper support and lattice, these microtubules will start to break down (a secondary damage) which can take longer to occur.”

CTE is a devastating brain disease for which there isn’t even an effective treatment.

Dr. Podell says that the “secondary damage” has not been proven to be a definitive explanation for how all of this happens over the years.

Why does CTE happen? He says that nobody knows the answer. Nobody truly understands why it behaves like a snowball rolling down a hill after the athlete retires.

There is conjecture that a genetic component plays a role in the development of CTE.

“It could be that all the damage to the brain was done at the time of insult,” affirms Dr. Podell, “and that it simply takes years for it to express itself, or that chronic traumatic encephalopathy itself actually worsens over time.

“Or it can simply be a cascading effect [think of the snowball analogy]. The only way to quantify CTE would be through a brain autopsy.”

Dr. Podell says that currently, there are techniques being developed for PET scanners to create an image of CTE in people who are still alive, “but we are not at a point to do serial quantification.”


Postmortem examinations of CTE victims reveal a pathological accumulation of plaques and tangles in the brains.

Dr. Podell explains: “We really have not advanced the science enough to know the cause of the disease course and progression of CTE.”