TUESDAY, July 23, 2019 (HealthDay News) -- Nearly three years ago, U.S. diplomats in Cuba began experiencing hearing loss, dizziness and memory problems -- in what the Trump administration attributed to an attack of unknown origin.
Now researchers say they have detected some "alterations" in the patients' brain structure and function -- though the significance, if any, is disputed.
The findings come from 40 U.S. embassy employees who, between 2016 and 2018, reported symptoms of what came to be known in the media as "Havana syndrome." They suffered from a range of concussion-like symptoms, including balance problems, memory lapses, difficulty concentrating, insomnia, headaches and nausea.
In 2017, the State Department said the employees may have been victims of a "sonic attack" that harmed their brains: Their symptoms reportedly arose after they heard intense, high-pitched sounds in their homes or hotel rooms.
But the alleged events remain unsolved. And there has been no objective evidence of any brain injuries.
Now, University of Pennsylvania researchers say they've potentially uncovered that evidence in MRI brain scans. As a group, the embassy workers' brains looked and functioned differently, in certain ways, compared to a group of healthy, "demographically similar" people.
Overall, the embassy workers had a smaller volume in the brain's white matter -- which contains the fibers that connect different parts of the brain. They also showed lower "functional connectivity" in areas of the brain involved in hearing and visual-spatial abilities.
The big caveat: It's not clear what the group differences signify.
The brain findings "don't represent any known pathology," said lead researcher Ragini Verma, a professor of radiology at Penn.
But, she said, the differences were seen in the cerebellum, a brain region involved in voluntary tasks, like walking and writing. And that fits with the pattern of symptoms the patients reported, according to Verma.
It's impossible to discern the cause, however.
"Brain imaging can only tell you there are differences," she said. "It can't tell you the 'what' or the 'how.'"
What's important, Verma said, is that the MRI findings offer "objective support" for the symptom reports.
Not everyone is convinced, however. The differences between the two groups were small and could be chance findings, said Dr. Sophia Frangou, a professor of psychiatry at Mount Sinai's Icahn School of Medicine in New York City.
When you go hunting for such brain disparities, you are bound to find something, according to Frangou, whose research uses brain-imaging techniques.
"This looks like a lot of incidental findings," she said.
"I think they wanted to do what they could for these patients, so they looked at everything," Frangou noted. "Unfortunately, nothing came up that was important."
The findings, published July 23 in the Journal of the American Medical Association, are based on a review of brain scans from 40 embassy workers. All went to Penn to have their symptoms evaluated, and underwent advanced MRI techniques that reveal details about the structure and functioning of the brain.
The imaging findings were compared with those from 48 healthy individuals who were similar in age, ethnicity and education.
But while there were some differences between the groups, there were not clear links between the patients' brain findings and their symptoms. A subgroup of 28 patients had tests of balance, eye motion and other abilities; researchers found little connection between those test scores and the MRI findings.
"The correlations weren't there," Verma said.
But, she added, that's a difficult bar to meet because this wasn't designed as a research study: The patients sought evaluation at various points after symptoms arose, and they did not uniformly undergo the same clinical testing and scoring.
Although Frangou did not see significance in the MRI differences, she was not dismissing the patients' symptoms.
"You can't always correlate imaging findings with symptoms," she said. "I think there are some things that go unexplained."
Some patients recovered from their symptoms and returned to work, while some others are still in rehabilitation, according to Verma. It might be informative, she said, to do post-rehab MRIs to see if the patients' brains show "compensatory changes" over time.
For now, the mystery remains unsolved. But Frangou saw "some degree of good news" in the MRI findings. "Nothing major was wrong with their brains," she said.
The U.S. National Institute of Neurological Disorders and Strokes has more on brain injuries.