THURSDAY, Feb. 15, 2018 (HealthDay News) -- They described hearing loud, unusual noises in either their homes or hotel rooms. Afterwards, they experienced concussion-like symptoms such as memory and thinking problems, headaches, dizziness and balance issues.
But the exact nature of what harmed more than 20 U.S. government personnel stationed in Havana, Cuba, last year remains mysterious, reports a team led by Dr. Douglas Smith of the University of Pennsylvania.
All that can be said for sure is that "we have identified a new syndrome that may have important public health implications," Smith said.
"None of these patients have suffered any type of blunt head trauma, yet the symptoms they describe and evaluations demonstrate are remarkably similar to those found in persistent concussion syndrome," noted Smith, who directs UPenn's Center for Brain Injury and Repair in Philadelphia.
Reports of the strange illnesses among U.S. diplomats stationed in Havana began to surface in late 2016 and continued through August of 2017, Smith's team reports in the Feb. 15 issue of the Journal of the American Medical Association.
Of the 80 embassy staff evaluated in the spring of 2017, "16 individuals were identified with similar exposure history and a constellation of neurological signs and symptoms" most often tied to concussion -- though none had suffered head injury, the researchers noted. Another eight cases developed over time.
The U.S. government convened an expert panel to look into the issue and that panel "came to consensus that the triage findings were most likely related to neurotrauma from a non-natural source," and requested further investigation, led by the UPenn team.
Initial testing done at the University of Miami also showed that the symptoms resembled those of concussion. Patients were then tested in a more detailed manner at UPenn facilities, beginning in the summer of 2017.
"In the new study, the Penn research team reports that patients experienced a wide variety of neurocognitive symptoms, including memory problems, trouble concentrating and processing information, and word-finding difficulties," a UPenn news release noted. "Visual focusing, dizziness and balance problems were also commonly reported during and after the sound incidents, and many patients subsequently suffered from headaches and sleep problems."
Overall, more than 20 people from the U.S. diplomatic staff in Havana have displayed such symptoms, Smith's group concluded.
The exact nature of what caused the symptoms -- and whether they are related to the strange noises heard by patients beforehand -- remain unclear, however. The research team said that noise "in the audible range is not known to cause persistent injury to the central nervous system."
Brain scans were largely inconclusive, the researchers added.
And the scientists also said that certain symptoms differed from those of a classic concussion. Patients developed pain in one ear, or tinnitus ("ringing in the ears") and balance issues, none of which is common after a concussion. Recovery for some patients was also much slower than that usually seen with concussion.
However, there was one upside to the study.
"The good news is that the symptoms appear to respond to rehabilitation interventions in a similar fashion, as we see in patients with persisting symptoms following a concussion," study author Dr. Randel Swanson said.
"While some patients reported that symptoms diminished on their own over time with no treatments, most individuals had symptoms that did not begin to improve until targeted therapies were initiated," said Swanson, an assistant professor of physical medicine and rehabilitation at UPenn.
He said that, based on what's been learned, a special rehabilitation program has been developed to help patients recover and return to their jobs.
There's more on concussion symptoms at the American Academy of Neurology.