Health officials say no evidence of mystery brain illness in New Brunswick

A report by Canadian officials has found no evidence of a new disease after hundreds of reports of neurological symptoms led to claims of a mystery brain condition.

The results of the investigation by New Brunswick's Chief Medical Officer of Health add to a growing body of research that suggests patients may have diagnosable illnesses instead.

About 500 people in New Brunswick and other provinces have been identified by neurologist Dr Alier Marrero as having unexplained neurological symptoms.

Officials said they also found no evidence to support Marrero's claims that patients' symptoms were caused by elevated levels of herbicides and heavy metals. The BBC has contacted Marrero for comment.

"Regardless of the findings of our investigation, the fact remains there are patients who are very ill and need support," said New Brunswick's chief medical officer of health Dr Yves Léger on Friday.

A BBC report published earlier this month questioned the legitimacy of the cluster of patients and asked whether hundreds may have been misdiagnosed by Marrero, and had suffered instead from known neurological illnesses.

The BBC report also revealed that at least one cluster patient had opted for death via medically assisted dying – with the mystery disease cited as the cause on the death certificate – and that at least one other patient was considering medically assisted dying.

The provincial study published on Friday examined the cases of 222 of Marrero's patients and reviewed results of extensive testing he had ordered on the patients which he said showed elevated levels of herbicides and heavy metals.

After comparisons with test results from among the broader population in the Atlantic Canada region, the province's findings showed that the herbicide levels among the cluster patients were normal, officials said.

A small number of patients did show higher than expected levels of heavy metals, the report found, but officials said it was difficult to confirm the results because of issues with the way they had been tested and they said there was no clear evidence to suggest the elevated levels could have led to adverse neurological health effects.

Officials said the provincial review was limited by several factors, including that some of Marrero's initial testing had not been done according to correct guidelines and that most patients had not been regularly retested to establish a pattern of elevated levels.

The report also found that close to 60% of patients in the group had also been seen by a second neurologist, and that none of the other neurologists had raised concerns to health authorities regarding the patients' conditions.

In response to the report's findings, health officials said that any patient referred to the province with an unexplained neurological condition would now have to be examined by two separate specialists.

Dr Léger told reporters on Friday that there was "mounting evidence that these patients have diagnosable conditions", adding that the province was "certainly concerned about that and about patient care".

He said the province's findings would be shared with Marrero, and that it was important the neurologist "understand what we've found from our analysis".

The data will also be shared with the Public Health Agency of Canada, Leger said, which will conduct a further review.

Sarah Nesbitt, a patient in the cluster and an environmental advocate, said she was concerned about the limitations of the study and that some patients did prove to have elevated levels of metals in their system.

But Nesbitt told the BBC she is hopeful that this a step towards helping patients, especially those with elevated levels, get more answers and additional support for their illnesses.

"At the end of the day, it's about finding the problem with the patients, helping them heal or cure or symptom manage," she said.

Friday's study is the second conducted by the province into the purported mystery illness.

Results of the previous study, which examined the first 48 patients in the cluster, was published in 2022 and similarly found no common exposures and concluded the patients were likely suffering from a range of different illnesses.

Last year, a separate research paper published by the JAMA neurology journal echoed the conclusions of the 2022 provincial report. The paper, based on a review of 25 cluster cases, found that the patients had all suffered from known and diagnosable illnesses including cancer and dementia.

The lead author of the JAMA paper, Dr Anthony Lang, told the BBC on Friday that the provincial report "confirms our suspicion or belief that there was no environmental factor that could have accounted for such a broad range of neurological problems".

"There was no consistent neurological disease that we had seen in this small group of patients we described," Lang added.

"So this just confirms exactly what we've suspected and really emphasises the suffering and pain that patients and families have had."

Nesbitt and other patients have rejected accusations that Marrero has misdiagnosed patients, and said he rightfully raised concerns about their test results of elevated metals.

She added some patients have expressed they do not want to see another neurologist "because they don't trust anybody anymore".

"He's a kind man, he's intelligent, he does due diligence," Nesbitt said, adding that he has done a considerable amount of testing on patients to help give them answers.

Marrero did not immediately reply to a request for comment about Friday's report. In September, he told the BBC that other senior federal and provincial scientists had also believed there was a novel syndrome in New Brunswick and that he was now being portrayed as the sole purveyor of the idea.

"They are trying to present me as it," he said. "I was part of it, but I was not it. The only difference is, when the table was empty, I stayed."