Dr. Neil Cashman, a neurologist at the University of British Columbia in Vancouver, who is investigating the illness, said it was a medical whodunit of the type seen only a couple of times a century.
“From the standpoint of a mystery, there is usually something horrible like a murder — in this case it is rapidly progressive dementia, and psychiatric manifestations, losing everything at once that is controlled by the brain and the spinal cord,” he said. “It is terrifying.”
But other medical experts questioned the condition’s novelty.
Dr. Michael D. Geschwind, a professor of neurology at the University of California, San Francisco, who is one of the world’s leading experts on rare neurological outbreaks, hasn’t studied the cases or autopsies of those affected. But he cautioned that what can seem like a new illness sometimes turns out to be a known disease that hasn’t been diagnosed. Those affected, he added, could end up suffering from a “grab bag” of disparate neurodegenerative diseases that were being linked together.
“Sometimes what seems to be a cluster turns out to be something else,” he said.
The disease was first observed in 2015 when a New Brunswick neurologist, Dr. Alier Marrero, saw a patient who presented a bizarre mix of symptoms including anxiety, depression, rapidly progressive dementia, muscle pains and frightening visual disturbances.
Three years later, he had eight total cases. The next year the total was 20. Then 38. Then 48.
The patients range in age from 18 to 84 and live primarily in two areas of New Brunswick: Moncton and the Acadian Peninsula.
Baffled by what he was observing, Dr. Marrero, a physician at Dr. Georges-L.-Dumont University Hospital Center in Moncton, ordered blood tests, spinal taps, M.R.I. scans and electroencephalograms.