Study finds no evidence of mystery brain disease in New Brunswick

By Brian Owens, The Courier

There is no evidence to support the existence of neurological syndrome of unknown cause in New Brunswick, according to a new independent scientific study.

The existence of a potential “mystery brain disease” in the province was first suggested in 2019 when a neurologist in Moncton identified several patients with unexplained neurodegenerative symptoms.

Since then more than 200 possible cases have been identified.

But an investigation by Public Health New Brunswick, published in 2022, concluded that there was “no evidence of a cluster of a neurological syndrome of unknown cause”. 

The latest study, published today in the journal JAMA Neurology, involved researchers in New Brunswick, Ontario, and Alberta and was led by Dr. Anthony Lang, a neurologist at the Kembril Brain Institute in Toronto. The study was carried out based on scientific curiosity and received no external funding, said Lang.

Lang and his colleagues re-examined the cases of 25 patients who had been diagnosed with a neurological syndrome of unknown cause. They carried out clinical evaluations of 14 patients, and autopsies on 11 more who had died.

In all 25 cases the researchers identified well-known conditions, including common neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease, traumatic brain injury, and cancer. A number of patients were also diagnosed with “functional neurological disorders” – what used to be called psychosomatic disorders – in which there is no physical brain abnormality, but cognitive function is altered.

“In 100 percent of the cases we saw we were able to make a neurological diagnosis,” said Lang. “This objective second evaluation came to the conclusion that there was no mystery disease.”

The wide variety of diagnoses also suggests that there is unlikely to be a single cause responsible for all of the illnesses.

“It’s not as though we’re dealing with a single neurodegenerative disease that could be caused by an environmental toxin,” he said.

Lang said determining whether environmental toxins are responsible for any of the cases would require an extensive epidemiological study to first show that there is a higher-than-expected rate of a particular neurodegenerative disorder like Parkinson’s in the area being studied.

“If we prove that there is a high incidence of selected disorders, not a broad spectrum of symptoms, then we can get serious about environment,” he said.

This latest study is not related to the ongoing review of the cases of undiagnosed neurological illness that is being conducted by the New Brunswick Chief Medical Officer of Health along with the Public Health Agency of Canada. Dr. Yves Leger, New Brunswick’s Chief Medical Officer of Health, said his office was not involved in Lang’s study, and did not receive an advance copy of the work.

“This study doesn’t change my office’s intention to complete its own investigation into cases of undiagnosed neurological illness in New Brunswick,” said Leger.

That review, launched in March 2025, is investigating concerns about potential environmental contaminants, but is not intended to determine whether there is a cluster of unknown disease, or its characteristics.

The final report is expected in late summer this year.

Dr. Alier Marrero, the Moncton neurologist who first identified the cluster of cases, said in an email that he disagrees with the conclusions of Lang’s study and is “appalled that a parallel investigation with a small number of patients has apparently been conducted for a long time, without our knowledge or our patients and families’ knowledge”.

Marrero said he has provided data for the government’s current review, including evidence of environmental exposures and rare autoimmune markers in many patients, and hopes this will help get to the bottom of the mystery.

“I trust that the current process of independent multidisciplinary scientific investigation and extensive files analysis that is underway by our Public Health authorities could provide much expected appropriate answers,” he said. “We are hopeful that this process would include not only comprehensive additional patients testing, but also testing for water, food, soil, and air samples in the affected areas, as well as additional patient support and effective prevention and treatments measures.”

But Lang cautioned that the records being used in the government’s review may not be reliable. He said that he and his colleagues found many inaccuracies in the records they reviewed. Some patients denied ever having some of the symptoms listed in their record, and some clinical features claimed to be present in the records were not there upon examination. 

“I’d have considerable concern about the quality and accuracy of any records being reviewed,” he said.