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Surveillance Continues on Pork Plant Workers Diagnosed with ‘Mystery’ Neuropathy


doi: 10.1097/01.NT.0000342330.69786.24
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Investigators provide clinical updates on a neuropathy that developed among workers at a Minnesota pork plant.

SALT LAKE CITY—It has been nearly one year since Mayo Clinic investigators determined that workers at a pork-processing plant in Austin, MN — who reported similar neuromuscular complaints — were suffering from a mysterious neuropathy. And the surveillance continues.

In a report here at the American Neurological Association (ANA) annual meeting in late September, the Mayo Clinic investigators who first identified the cluster last February offered updates on their findings.

“We are describing a newly recognized sensory-predominant painful polyradiculoneuropathy that occurs in pork-processing workers exposed to aerosolized pig brain,” said Jennifer A. Tracy, MD, a muscle fellow in the Department of Neurology at the Mayo Clinic in Rochester, MN.

“We think it's most likely to be an autoimmune mechanism based upon a high CSF protein content, enlarged nerve roots on MRI, abnormal inflammation on nerve biopsy, and abnormal autoantibody profiles.”

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Twenty-one employees — all of who worked in a “warm room” of a plant, in which pig brains were removed by blowing compressed air through the cranium — developed neuromuscular symptoms and alerted Mayo Clinic neurologists.

Eleven were women and 10 were Hispanic. Nearly all patients had aching and burning distal limb pain, and 17 had weakness, usually mild. Fourteen workers had sensory loss.

Nerve conduction studies showed abnormalities in at least one test in 16 of 19 patients, including prolonged distal motor latencies in 12 of 19, prolonged F-wave latencies in 13 of 19, and prolonged trigeminal blink latencies in 10 of 15.

“It is really the most distal and most proximal areas of the nerve that are predominantly affected,” Dr. Tracy said.

CSF protein content was elevated in 15 of 19 workers, with a median of 99 mg/dL and a range of 23 to 231 mg/dL.

Dr. Tracy also said that “there was CNS involvement in two patients.”

Three workers from an Indiana pork processing plant where pig brains were also removed by compressed air, developed similar problems and were also examined by Mayo researchers. “Essentially they had the same clinical manifestations, the same electrophysiologic and MRI findings as well as the other measures,” Dr. Tracy said.

Former ANA president Arthur Asbury, MD, a professor of neurology at the University of Pennsylvania School of Medicine and a leader in neuropathy research, praised the Mayo study.

“I think it's been very professionally done,” he said. “They looked at all the right stuff.”

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Lyle Ostrow, MD, a resident at Johns Hopkins who attended Tracy's poster presentation and question-and-answer session, wondered why this syndrome was being observed only now.

“This technique of aerosolizing the brain is not new, right? It's something that's been going on for a while,” he said. “What changed?”

Dr. Tracy suggested that the rapid increase in production at the plant might have something to do with it. The plant formerly processed about 1,000 pigs per hour but more recently increased production to 1,400 pigs an hour. “When the procedure was slower, it was also neater,” Dr. Tracy said. “Now they're trying to get through them faster, and there's more splatter.”

“Another possible reason might be that this condition has existed for a longer time but was not recognized until now,” said P. James B. Dyck, MD, of the Mayo neurology department, who was involved in the studies. “It might have gone unnoticed until now because of the high turnover at the plant, and because many workers are non-English speakers and less likely to report health problems.

“In fact, in Indiana, one patient told us she replaced a worker who got sick from doing brain removals.”

“We've been trying to find a clear answer as to when the aerosolization technique started,” Dr. Tracy said. “Because the Minnesota Department of Health is doing the epidemiological part of the study, we have not been dealing directly with the company. We are aware that the procedure has been going on for a number of years prior to this outbreak, but have gotten different answers to this question when we ask our patients how long this technique has been used.”

The company voluntarily terminated the practice of using air-compression to remove the brains in December of 2007 after suspicion arose that the brain mist might be making the workers sick.

The effect of treatment on the workers remains to be seen, Dr. Tracy said. Some of the workers have undergone immunomodulatory treatment, she said. The condition of the workers generally improved gradually once they stopped having exposure to the aerosolized brain, she said.

“All of them had some improvement,” Dr. Tracy said. “At this stage, we're still working on analysis of the data to see if there's a significant difference between treated and untreated patients.”

For More on the Pork Plant Neuropathy Visit for past reports on the pork plant neuropathy:

  • “Antibody Pattern Discovered for Pork Plant Illness,” June 5, 2008.
  • “Alert to Neurologists — Help Needed to Help Solve Mysterious Neurological Illness at Minnesota Pork Plant,” Feb. 7, 2008.
  • “Neurologists Asked to Report Neuropathy Cases to CDC,” Feb. 21, 2008.
©2008 American Academy of Neurology