Province report finds no environmental cause for neurological symptoms in New Brunswick patients
A New Brunswick health review found no evidence that herbicides or metals caused neurological symptoms in patients of one neurologist, and calls for procedural changes and further review.
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By Torontoer Staff
A New Brunswick investigation has found no environmental link to the range of neurological symptoms reported by hundreds of patients seen by a single neurologist, the province’s Chief Medical Officer of Health, Yves Léger, said Friday. The review, which analysed data from 222 patients, did not find herbicides or metals at levels likely to have contributed to illness for most people in the group.
The report does not resolve why patients continue to experience serious, unexplained neurological problems, and the province is moving forward with recommendations and an external review requested by patient representatives.
What the investigation examined
Health officials launched the review after Dr. Alier Marrero, a neurologist practising in New Brunswick, raised concerns in 2023 about a growing number of patients with undiagnosed neurological illness who also had elevated levels of herbicides or metals detected in their bodies. The provincial investigation was tasked with determining whether there was any environmental connection, including exposures that could plausibly explain the symptoms reported.
Investigators reviewed clinical and laboratory data from 222 patients and assessed available environmental and biological testing. The province has not released a detailed catalogue of every test or laboratory method used in the publicly available summary.
Key findings
According to the report, the pattern of results does not suggest a common environmental exposure that could account for the majority of cases. In particular, measured levels of herbicides and metals were not consistent with exposures at concentrations that would typically be expected to cause the kinds of neurological illness described.
Earlier reviews had already found no evidence of a single, shared diagnosable illness among the patients. The new report adds that, on the environmental front, the data do not support a unifying toxic cause.
Regardless of the findings of our investigation, the fact remains there are patients who are very ill and need support.
Dr. Yves Léger, Chief Medical Officer of Health
Recommendations and next steps
The report outlines steps the province says it will take to strengthen case identification and oversight. One formal change is a requirement that two specialists assess a patient before they are reported as a new case of an unknown neurological illness. The goal is to standardise how cases are classified and reduce the risk of misidentification.
The provincial government has asked the Public Health Agency of Canada to conduct a separate review of the full dataset from the investigation. That request followed an appeal from patient representatives who sought an independent examination of the findings and the underlying data.
- Investigation reviewed data from 222 patients associated with one neurologist
- No environmental exposure identified that plausibly explains symptoms for most patients
- New procedural requirement: two specialists must confirm cases before official reporting
- Public Health Agency of Canada asked to do an independent review at the request of patient representatives
What this means for patients and clinicians
The report does not provide a clinical explanation that would change care for patients, and health officials said attention will shift to implementing recommendations and ensuring patients receive appropriate clinical support. Clinicians will be asked to follow the new case confirmation process, while public health agencies carry out the independent review.
Patient advocates have for months pressed for transparency and external oversight. The provincial request to the federal agency responds to some of those calls, but it may take time for an independent analysis to conclude and for its findings to be made public.
Background and ongoing questions
The situation dates to 2023, when Dr. Marrero publicly raised concerns after seeing a number of patients with varied neurological complaints and reporting abnormal tests for pesticides and metals in some individuals. Multiple investigations since then have sought, so far without success, to identify a single cause that links the cases.
Health officials and clinicians say further work will be needed to support patients, to improve diagnostic pathways, and to ensure any future clusters of unexplained illness are investigated with clear standards and independent oversight.
For now, the province’s report closes one line of inquiry by concluding that environmental herbicide or metal exposure is unlikely to explain the symptoms experienced by most patients in this group. Authorities have committed to follow-up steps and to a federal review of the data.
New Brunswickpublic healthneurologyinvestigationYves Léger
