Washington —

A series of advanced tests found no brain damage or degeneration among U.S. diplomats and other government employees suffering from a mysterious health problem once known as “Havana syndrome,” researchers reported Monday.

Nearly five years of research by the National Institutes of Health offers no explanation for symptoms such as headaches, balance problems and difficulty thinking and sleeping, which were first reported in Cuba in 2016 and later reported by hundreds of U.S. personnel in multiple countries.

But it does contradict some earlier findings that raised concerns about brain damage in people experiencing what the State Department now calls “unusual health events.”

“These are people who have real symptoms and are going through a very difficult time,” said Dr. Leighton Chan, director of rehabilitation medicine at the National Institutes of Health, who helped lead the study. “They can be very serious, disabling and difficult to treat.”

However, when the Havana syndrome patients were compared to healthy government workers with similar jobs, including some at the same embassy, ​​sophisticated MRI scans found no brain volume, structure or white matter (signs of damage or degeneration) There are significant differences. There were also no significant differences in cognitive and other tests, according to findings published in the Journal of the American Medical Association.

While this doesn’t rule out the possibility of brief impairment at the onset of symptoms, the researchers say the good news is that they were unable to detect in the brain scans the typical long-term markers after trauma or stroke.

That “should be reassuring to patients,” said study co-author Louis French, a neuropsychologist who treats Havana syndrome at Walter Reed National Military Medical Center. “It allows us to focus on the here and now and get people back where they should be.”

A subset of Havana syndrome cases (about 28%) are diagnosed with a balance problem called persistent postural perceptual dizziness (PPPD). It is associated with inner ear problems and severe stress, and results when certain brain networks are not injured but cannot communicate properly. French calls it a “maladaptive response,” like the way people who hunch over to relieve back pain develop postural problems even after the pain goes away.

Havana syndrome participants reported more fatigue, post-traumatic stress symptoms, and depression.

The findings are the latest to unravel a mystery that began when staff at the U.S. Embassy in Cuba sought medical care for hearing loss and tinnitus after reporting sudden, strange noises.

Earlier, there were concerns that Russia or other countries might use some form of directed energy to attack Americans. But last year, U.S. intelligence agencies said there was no indication that a foreign adversary was involved and that most cases appeared to have different causes, ranging from undiagnosed illnesses to environmental factors.

Some patients accuse the government of ignoring their disease. In an editorial in the Journal of the American Medical Association on Monday, a scientist called for more research to prepare for the next such health mystery, warning that the NIH study design combined with the current There are limitations in medical technology that may miss some clues.

“One might suspect that nothing happened in these cases or that nothing serious happened. That would be unwise,” wrote Dr. David Lehrman of Stanford University, who in 2022 became the head of a government-appointed panel. members, the team could not rule out the possibility that energy in the form of pulses could explain some of the cases.

The NIH study, which began in 2018 and included more than 80 people with Havana syndrome, was not designed to examine the possibility of certain weapons or other triggers of Havana syndrome symptoms. Chen said the findings did not contradict the intelligence agency’s conclusions.

If there is some “external phenomenon” behind the symptoms, “it does not lead to sustained or detectable pathophysiological changes,” he said.

The State Department said it is reviewing the NIH’s findings but that its first priority is to ensure that affected employees and family members “are treated with respect and compassion and receive timely medical care and all benefits to which they are entitled.”