Study finds no evidence to support New Brunswick’s mystery brain disease

FREDERICTON — There is no evidence to support claims of a mystery brain disease in New Brunswick, says a new study that suggests the media may have played a role in feeding patients’ fears.

Published Wednesday in the journal JAMA Neurology, the study reviewed the cases of 25 patients evaluated at two hospitals in New Brunswick and Ontario and found their symptoms could be traced back to several known neurodegenerative and non-neurodegenerative conditions.

“Unfounded concerns that a potentially fatal mystery disease, possibly induced by an environmental toxin, is causing the patients’ neurological symptoms has been amplified in traditional and social media,” the study said.

Nearly 400 New Brunswick residents – mostly in the Acadian Peninsula and Moncton areas – have reported symptoms of what the province’s Health Department has called a “neurological syndrome of unknown cause.” Symptoms include memory problems, balance issues, behavioural changes, muscle spasms and bursts of intense pain.

The Health Department under the former Progressive Conservative government in 2022 said a team of six neurologists and other health experts found no evidence that a cluster of cases existed after their investigation of 48 patients – 46 of them referred by a single neurologist: Dr. Alier Marrero. But after the list of patients reporting symptoms grew to almost 400, the Liberals, who won last year’s provincial election, promised to reopen the investigation.

Now, the JAMA study by authors affiliated with the University of Toronto, New Brunswick’s Horizon Health Network and other Canadian institutions seems to back up the initial research under the Tory government. Data for the study was collected between November 2023 and March 2025, and included initial health records and followups, as well as demographic information and autopsy reports when available.

The study said well-known conditions such as traumatic brain injury or metastatic cancer were identified in all 25 patients, who were evaluated at New Brunswick’s Horizon Health Network and Ontario’s University Health Network. As well, there was “strong evidence” against an exposure to an environmental toxin. The condition of some of the patients is “complex” and warrants a second opinion, the study said. “However, it appears few patients sought this.”

That the illness has gained a reputation as a “mystery brain disease” can be attributed to several factors such as a decreased trust in public health institutions following the COVID-19 pandemic and general misinformation, the study said.

“Misinformation regarding this cluster (of cases) has proliferated in both traditional and social media, from not only the predictable and easily identifiable groups co-opting the crisis to suit their agenda, such as anti-vaccine advocates, but also those who are unknowingly amplifying an incorrect diagnosis from their physician,” it said.

Data showed patients could be suffering from other diagnosable neurological conditions and could potentially benefit from a multidisciplinary treatment, the study said. It noted that some patients who got a second opinion rejected the diagnosis, choosing to believe they were suffering from an unknown neurological disease.

“Education, reassurance, and mental health support should also be prioritized for patients and families who have been profoundly impacted by claims that a potentially fatal mystery disease continues to affect them,” the study said.

Meanwhile, Marrero, the neurologist who was the first to diagnose the patients with a mystery illness, is defending his work. In an email on Wednesday, the doctor said he has evaluated more than 500 patients and provided a “significant amount of unequivocal, sometimes critical environmental exposure evidence, as well as rare autoimmune markers in many of them.”

He “profoundly” disagrees with the JAMA study’s conclusions and has a number of questions regarding its methods and content.

The province’s chief medical officer, Dr. Yves Léger, said in March his office would review 222 patient files with the Public Health Agency of Canada into the illness and results could be expected by the end of May. In an email statement on Wednesday, Léger said the new study doesn’t change his office’s intention to complete its own investigation.

Dr. Anthony Lang, co-author of the JAMA study, said the patients are suffering from a variety of symptoms, and need to be evaluated by experts who have an open mind to what might be the cause, rather than a fixed belief that they’re dealing with a mystery disease.

“I think the problem is that if somebody believes that they’re making a diagnosis, a single diagnosis, then everything becomes that diagnosis,” said Lang, who holds the Jack Clark Chair for Parkinson’s disease research at the University of Toronto.

“There’s nothing uniform about these patients, and therefore one can’t claim that you have a large cohort of an unusual condition in a small region.”

Lang said he got involved because he started hearing about a mystery disease but had not seen proper scientific documentation demonstrating that any of the patients had a rare neurological disorder.

“It should be concerning to the media and to the health-care system that no other physicians are making similar claims,” he said. “It’s not as if all physicians in New Brunswick are suddenly beginning to realize that they have an epidemic of neurological diseases that can’t be explained or far more Parkinson’s or Alzheimer’s or other conditions that are far more frequent than expected.”

Patients could have been helped, he said, had Marrero sought guidance from his peers. “One of the problems in neurology is that many neurological diseases don’t have clear diagnostic tests,” Lang noted.

The 2022 report from New Brunswick’s Health Department attributed some of the symptoms to other conditions including Alzheimer’s, dementia, Parkinson’s, paranoid schizophrenia, chronic fatigue, severe anxiety disorder, and cancer.

Sarah Nesbitt, one of Marrero’s patients, said she stands behind the doctor, adding that her symptoms were caused by an environmental toxin. She said she saw her family physician and was evaluated at the Moncton Interdisciplinary Neurodegenerative Diseases clinic, before she was referred to Marrero. However, she said she has not been seen by a neurologist other than him.

“This man is a wise, intelligent, kind, educated man,” she said, describing Marrero. “He’s very thorough.”

This report by The Canadian Press was first published May 7, 2025.

Hina Alam, The Canadian Press