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By Maggie Fox

Staff pulled out of the U.S. embassy to Cuba last fall have symptoms that look similar to those caused by concussions, doctors report.

Medical exams of 21 of the staffers show they had headaches, balance problems, sleep disturbances and visual and hearing problems, a team at the University of Pennsylvania reported.

Objective measurements confirm that most had problems with thinking, balance and eye control. Most are still undergoing therapy, the team reports in the Journal of the American Medical Association.

“So, this is really concussion without concussion. I mean it really looks like concussion without the history at the head trauma," said Dr. Douglas Smith, director of the Center for Brain Injury and Repair at Penn’s Perelman School of Medicine.

The medical reports add more to the mystery surrounding events at the U.S. embassy in Havana. Cuban officials have denied they did anything to the staffers.

Starting in 2016, some staff reported hearing strange sounds and said they were suffering headaches and other symptoms. The federal government started pulling staff out in September and expelled some Cuban embassy staff from Washington in October.

But the descriptions given by the staffers of what happened to them baffled medical and national security experts alike. No known weapon or device causes such symptoms in a way the events were described.

“For 18 of the 21 individuals, there were reports of hearing a novel, localized sound at the onset of symptoms in their homes and hotel rooms,” Smith and colleagues wrote.

“Affected individuals described the sounds as directional, intensely loud, and with pure and sustained tonality,” they added.

“Of the patients, high-pitched sound was reported by 16, although two noted a low-pitched sound. Words used to describe the sound include ‘buzzing,’ ‘grinding metal,’ ‘piercing squeals,’ and ‘humming’,” they added.

Five of the staffers said the sounds were so loud they covered their ears.

“The sounds were often associated with pressurelike or vibratory sensory stimuli, which were also experienced by two of the three patients who did not hear a sound,” the doctors wrote.

“The sensory stimuli were likened to air ‘baffling’ inside a moving car with the windows partially rolled down.”

Loud sounds can affect hearing but they are not known to cause brain damage. Yet the staff reported persistent and troubling symptoms.

Most immediately felt a need to get away, and many felt confused, nauseated and had a headache.

They later felt foggy, had trouble concentrating and felt nervous or irritable. “For at least six individuals, a clear change in work performance was noted by supervisors and colleagues,” the medical team wrote.

The staff did not appear to be malingering,the doctors concluded.

“Rather than seeking time away from the workplace, the patients were largely determined to continue to work or return to full duty, even when encouraged by health care professionals to take sick leave,” Smith and colleagues wrote.

And while some of the symptoms overlap with concussion, not all did.

“In contrast to classic concussions, most patients referred following suspected exposure in Havana exhibited significant impairment that persisted for months with no significant improvement in multiple cases until rehabilitation was initiated,” the doctors said.

“For example, individuals experienced unilateral ear pain and tinnitus after exposure,” they added. And they had balance problems not often seen with concussion.

“This raises the question of whether, in the absence of physical trauma, central nervous system injury may be sustained through exposure to sound or other phenomena.”

Outside experts said the findings raised as many questions as they answered.

“Before reaching any definitive conclusions, additional evidence must be obtained and rigorously and objectively evaluated,” neurologists Dr. Christopher Muth of Rush University Medical Center in Chicago and Dr. Steven Lewis of the Lehigh Valley Health Network in Allentown, Pennsylvania wrote in a commentary.

They said it was possible the affected staff had compared notes before they were examined, and that much of the evidence was based on their own reports, which could have been colored by time.

They also noted that age and other conditions can cause many of the symptoms described. The Penn team was unable to provide many details about the patients, such as age or sex, in the interest of protecting their privacy.

“Nonetheless, the similarities among the 21 cases merit consideration of a common medical, environmental, or psychological event as the potential cause,” Muth and Lewis said.

“The authors emphasize similarities to the symptoms seen in concussion, with the notable exception that the individuals in this case series did not experience physical head trauma, as is typical in concussion or other forms of traumatic brain injury,” they added.

“This raises the question of whether, in the absence of physical trauma, central nervous system injury may be sustained through exposure to sound or other phenomena.”