The earliest medical exams of 25 US diplomats in Cuba reporting dizziness, foggy thinking, and related injuries suggest they all had inner ear damage possibly caused by noise or pressure, according to a new study. Many experts are critical of these findings, however, saying this two-year-old medical mystery remains unsolved as ever.

In 2016, US and Canadian diplomats in Havana began reporting neurological symptoms tied to a suspected acoustic weapon of some kind targeting their homes. Then-secretary of state Rex Tillerson called the injuries “health attacks” and withdrew more than half of the Havana embassy staff in response a year later, in a still continuing diplomatic uproar marked by wide disagreement among medical experts over the cause of the mysterious injuries.

In the new study, released on Wednesday, a team of blast injury experts led by otolaryngologist Michael Hoffer of the University of Miami report on the first examinations of diplomatic personnel, 15 men and 10 women. The most common injury was dizziness, the study found, and 100% of the diplomats bore signs of an inner ear injury.

Just like past investigations, the researchers were unable to pin down a cause of the damage, but they said a sonic weapon was possible.

“It does not seem imprudent to speculate that a highly specific unidentified energy exposure, perceived as a sound or pressure, could be producing an inner ear disturbance or demonstrate findings suggestive of a mild traumatic brain injury,” the study concludes.

But independent experts asked by BuzzFeed News called that suggestion unlikely, saying the data presented in the study could just as easily point to something other than an attack. Some observers have suggested mass hysteria, for example, or an infectious disease.

“The authors assume from the get-go that the subjects have some kind of ‘disorder,’ which has not been established with any certainty,” neuroscientist John Van Horn of the University of Southern California told BuzzFeed News.

Critics also took issue with the authors’ decision to discard from the study 10 other diplomats, all housemates who were unaffected, including two who briefly heard the noises. The authors said that the differences among housemates showed that the exposure “was both fairly precise and delimited in space and time.” But Van Horn pointed out that it is still unclear what, if anything, the diplomats were exposed to.

An editorial in JAMA earlier this year raised the possibility of an infection causing the problem, while other experts have noted that vertigo, deafness, and other neurologic ailments are common in mass hysteria events. Those explanations aren’t examined in the new study, nor is the State Department’s role in the research.

The team tested the 25 diplomats in Miami. The 10 housemates were examined there but not subjected to the study tests, and 105 other unaffected diplomatic and military personnel at the embassy in Havana had medical exams as a precaution. All of the reports of initial symptoms were based on personal recall by the 25 injured diplomats 4 to 60 days after their exposure. “The affected individuals all reported direct exposure to either noise or pressure,” according to the study, followed by intense ear pain and ringing.

Of the 25, 13 failed an eye-movement test for vertigo, and 23 reported dizziness. Overall, the breadth of symptoms from dizziness to failed eye-movement measures does seem to point to an inner ear injury of some kind, perhaps pointing to a concussion-like syndrome suggested by University of Pennsylvania researchers who had examined 21 of the diplomats.

At the same time, the tests found only two diplomats with hearing loss, despite the ear pain and tinnitus, and both of those had hearing problems before the events in Havana. Only six of the injured diplomats reported headaches, a signature of head trauma, about the same rate as their unaffected housemates.

“These are very ambiguous results,” neuroscientist Mark Cohen of UCLA told BuzzFeed News. There is no real overlap in symptoms among the diplomats, aside from dizziness, which is tough to measure objectively. That points away from a single cause for the symptoms, pressure beam or otherwise, he said. And the decision to exclude the housemates from testing was a mistake. “They had a very nice control group and they didn’t use them.”

There is no way of knowing how often the difficulties reported by the diplomats turn up in any group of middle-aged people, Cohen added. “I have no reason to doubt the symptoms reported by the people aren’t real, aside from hearing loss which tests show isn’t there, but I have no way to tell if they are different from random, either.”

The study was published in a low-ranked journal, Laryngoscope Investigative Otolaryngology, where Hoffer is an associate editor. The authors seem to have had greater ambitions a year ago, however, when they were preparing to submit it to the prestigious New England Journal of Medicine.

As a spokesperson for the State Department told BuzzFeed News by email: “Dr. Hoffer submitted a proposed New England Journal of Medicine article which the Department received in December 2017 and cleared on February 20, 2018. The Department has no additional information regarding the status of that article.”

Emily Tamkin contributed reporting to this story.