Research published today explores the mystery behind a reported cluster of an unknown brain disease in New Brunswick, Canada.
Neurologists in Canada led the study, published Wednesday in JAMA Neurology. They analyzed over two dozen suspected cases of the mystery illness, finding no evidence that the patients’ symptoms were caused by a novel disease or shared environmental trigger. This study is unlikely to be the final word, however, as the local government has launched a new investigation into the apparent cluster.
In March 2021, a memo from New Brunswick health officials to health care workers was leaked to the press. It warned doctors that an unusual number of residents in the area were being diagnosed with neurological symptoms that had no clear cause. These symptoms included dementia, rapid weight loss, trouble moving, and hallucinations. Early tests appeared to rule out possible known culprits for the cluster, such as prions—rogue, potentially transmissible, proteins that slowly destroy the brain.
Neurologist Alier Marrero was the first doctor to come across these cases, some of which may date as far back as 2013. In 2020, he began to report them to officials at the Public Health New Brunswick. The cases were classified as a neurological syndrome of unknown cause (NSUC). By the time the memo became public, 48 possible NSUC cases had been identified, with several patients having died from their symptoms.
PHNB officials eventually created an oversight committee of experts to review these early cases. In February 2022, the committee published its findings. They concluded that the patients did not seem to share a “common illness”—instead, their symptoms were caused by a variety of known neurological conditions. Later that same month, the New Brunswick government declared the investigation closed.
But the story didn’t end there. Marrero, along with people who believe they have NSUC and other advocates, has continued to argue that the cluster is real—and potentially much larger than officially reported, possibly affecting hundreds. They’ve further alleged that local and federal governments hampered the original investigation by barring some experts from participating; by failing to include many suspected cases for consideration; and by ignoring possible causes, such as certain environmental agents.
This new study is the work of neurologists from across Canada, including experts from the Moncton Interdisciplinary Neurodegenerative Diseases (MIND) Clinic in New Brunswick, where many NSUC patients were first evaluated. The researchers analyzed autopsy data from 11 people who died after being diagnosed with NSUC, and re-examined 14 other patients who agreed to get a second evaluation at the MIND Clinic.
As with the earlier investigation, the researchers failed to find a single underlying cause, let alone a novel one, for the illnesses. They concluded that all 25 cases could be explained by other known conditions and causes, including Alzheimer’s disease, Parkinson’s, and traumatic brain injury. They also argued that at least some of the NSUC cases may have been misdiagnosed due to inaccurate clinical assessments and an overreliance on non-definitive tests that could be misinterpreted, such as electroencephalograms (EEGs).
“We have found no support for the existence of an undiagnosed mystery disease in New Brunswick,” the authors wrote. “The broad range of very different, well-recognized diseases diagnosed is also strong evidence against a single environmental toxin causing the patients’ symptoms.”
These cases are only a small sample of the potential suspected cases of NSUC in New Brunswick, however, and the findings are unlikely to close the door on the matter.
Marrero continues to urge local officials to investigate the cluster and has submitted dozens more reports of suspected cases. Last year, during the provincial election campaign in New Brunswick, candidate Susan Holt promised that she would reopen the government’s investigation if elected premier—a promise she has kept.
The Office of the Chief Medical Officer of Health in New Brunswick, the Vitalité Health Network, and the Public Health Agency of Canada, are now once again investigating the cluster. Yves Léger, the chief medical officer of health, stated in March that the office has begun to analyze 222 cases referred to it by Marrero. A public report on the cluster is expected by this summer.
In their paper, the researchers noted that over 100 patients diagnosed with NSUC were offered a second evaluation at the MIND Clinic in 2022, but most declined or didn’t respond. In some cases, they added, people who were given a different diagnosis the second time refused to accept it. And they argue that the initial public and media fervor over these cases, along with other factors, may have impeded people from trusting other doctors or alternative explanations.
“Clear and transparent communication strategies to report the much-needed reevaluations are required,” they wrote. “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.”
