Doctors say they have found a way to diagnose Chronic Traumatic Encephalopathy (CTE) — the degenerative disease that is found in the brains of former professional football players — in a living person.

If true, their technique could change the way the disease is detected, studied, and treated.

But there’s a caveat.

The doctors at the University of California, Los Angeles (UCLA), have only made the diagnosis in one person so far.

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One man’s diagnosis

The doctors published a case study of a 51-year-old man who came to the UCLA Psychiatry Cognitive Health Clinic and Research Program earlier this year complaining of memory loss, trouble focusing, and mood swings.

He and his wife had been seeking an accurate diagnosis for years. Other doctors told them he had bipolar disorder and attention deficit hyperactivity disorder (ADHD). But those diagnoses were unsatisfying.

“He was being told a medical explanation that didn’t fit his story,” Dr. David Merrill, an assistant clinical professor at UCLA, and co-author of study, told Healthline.

Both bipolar disorder and ADHD usually manifest earlier in life. This patient had never experienced problems with his attention span or his mood before middle age.

So Merrill and his team did an MRI. Using new software to quantify the brain’s volume and compare it with volumes found in average brains, they found that certain regions of the man’s brain — regions associated with CTE — were smaller than average.

And when they compared this MRI with one taken in 2012, they found that the man’s brain had been shrinking over time. In fact, he had lost 14 percent of his total gray matter in the past four years.

But why CTE? The patient wasn’t a National Football League (NFL) player or professional athlete of any kind.

He had, however, played football in high school, the doctors found out.

“As part of the patient’s high school football training, he was taught to go ‘head to head’ in his play, projecting his head forward to absorb impacts. It was seen as a positive to have ‘a lot of nicks on your helmet from the opposing players,’” the authors wrote in the study, which was published today in the American Journal of Geriatric Psychiatry.

They estimated the man received about 900 blows to the head throughout his high school career.

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Questioning the diagnosis

Although the condition is associated with NFL players, CTE has been found in the brains of amateur athletes before.

Last year, the Mayo Clinic announced that a third of the donated brains of men who had played contact sports in their youth showed signs of CTE.

In 2006, 18-year-old football and rugby player Eric Pelly died 10 days after he suffered a concussion — one of a handful in his young life. An autopsy later confirmed CTE.

Despite these confirmed cases in amateur athletes, Dr. Ann McKee, a neuropathologist at Boston University who diagnosed CTE in the brains of many NFL players, is skeptical of the UCLA doctors’ claims.

“There are many things that could be causing his symptoms,” she told Healthline.

The brain shrinkage the doctors observed in the man’s MRI images isn’t enough to make that diagnosis, she said.

Currently, the only accepted way to diagnose CTE is to look deep within the brain for tangled bundles of the protein tau.

In people with the disorder, the protein malfunctions and jams the flow of information between brain cells. Finding those bundles requires taking sections of the brain, so it’s only possible to do during an autopsy.

The UCLA team asserts that the regions of the brain that shrank in their patient are the same regions where tau protein buildup and atrophy occur in known cases of CTE. But they acknowledge that their results are preliminary.

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Past warnings

Several members of the team that published today’s case study, which includes Dr. Bennet Omalu, portrayed by Will Smith in the 2015 movie “Concussion,” have previously been accused of jumping the gun.

Last year, the FDA sent a warning letter to the company TauMark ordering them to stop advertising brain scans with their proprietary protein tag, FDDNP. The company’s claims of the tag’s safety and effectiveness had not yet been evaluated, the agency said.

A number of researchers are working on similar tags as a means of diagnosing CTE in living brains.

Using this method, a patient would be injected with a radioactive tag that binds itself to the tau protein. Then, the dyed protein would show up in the brain under a PET scan. McKee thinks this is the most promising venue for detecting CTE in a living person.

Merrill concedes that he can’t definitely diagnose this patient with CTE. But he says that it’s an explanation that makes sense for the man and provides him and his wife some relief.

“It’s the old saying that knowing is half the battle,” Merrill said.

For the patient and his family, he said, it’s important to understand that it’s not weak will, it’s not selfishness — and “it’s not all in your head.”