Findings in Pork Workers With Novel Neurological Illness Reported for the First Time

Caroline Cassels

April 17, 2008

April 17, 2008 (Chicago, Illinois) — Initial findings on a mysterious neurological illness in a cluster of pork workers indicate this is a new disorder with distinct serologic and radiographic characteristics.

Here at a late-breaking session of the American Academy of Neurology 60th Annual Meeting, Daniel Lachance, MD, from the Mayo Clinic in Rochester, Minnesota, presented findings on 18 confirmed cases of what investigators are calling immune polyradiculoneuropathy or progressive inflammatory neuropathy.

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"To date, accounts of this condition have been reported only in the lay press. This meeting is the first opportunity we've had to officially present a description of the disorder and these initial findings to an audience of our peers," Dr. Lachance told Medscape Neurology & Neurosurgery.

Reports of the illness, which includes symptoms ranging from a transverse myelitis syndrome (in a single patient), to pain, numbness, and tingling in the extremities, fatigue, and weakness, were first made public in December 2007.

Limited Use of Extraction Procedure in the United States

All of the affected slaughterhouse workers had jobs harvesting pig brains, which involved the use of a compressed-air gun to remove the organs from the animals' skulls.

At this point, said Dr. Lachance, the working hypothesis is that the air gun aerosolized the brain matter, turning it into a fine mist, which workers then inhaled, setting up an immune response and subsequent inflammation in the spinal cord and root nerves.

In September 2007, a Mayo Clinic Health System Spanish interpreter and nursing staff at the pork-processing plant, which is located in Austin, Minnesota, reported this pattern of symptoms in 12 suspected cases to a senior family physician, who contacted Dr. Lachance, a neurologist with a subspecialty in neuroimmunology.

In November 2007, the Minnesota Department of Health launched an investigation of the plant, and in December 2007, the plant voluntarily stopped using compressed air guns to process the brains. The plant employs 1200 workers, 500 of whom work in the "warm room" where the pig brains are butchered.

According to James Sejvar, MD, from the Centers for Disease Control and Prevention, in Atlanta, Georgia, who collaborated with the Minnesota Department of Health on the initial investigation, use of compressed-air devices to extract pig brains appears to be limited to 3 plants in the United States. However, he added, it is not known whether these devices are used internationally.

Novel Antibody Pattern

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The 18 cases underwent standardized clinical and laboratory testing at the Mayo Clinic's peripheral nerve center, which included assessments of autonomic nervous system function, cerebral spinal fluid (CSF) analysis, magnetic resonance imaging (MRI), and serologic testing.

Of note, said Dr. Lachance, was the fact that 100% of the subjects had a novel profile of neural antibodies, including an IgG immunostaining pattern.

"In the Mayo Clinic's neuroimmunology laboratory experience, where we analyze 10,000 to 20,000 [serum samples] per year, we have never seen this particular antibody pattern before," he said.

In addition, 13 of 15 patients had elevated CSF protein levels, and MRI findings revealed that the majority of subjects also had enlarged, sometimes thickened, spinal roots.

To date, said Dr. Lachance, none of the patients has completely recovered, none has progressed, and most have returned to work. At this point, he said, there is no indication that this is either an infectious or food-borne illness.

"So far as we know, the only commonality [among the affected individuals] has been the brain-extraction procedure that has been employed at these plants," said Dr. Lachance.

Ongoing Investigation

Additional suspected cases have been reported. Of these, 5 subjects are workers from a pork-processing plant in Indiana and another single suspected case is in a worker from a pork slaughterhouse in Nebraska.

Dr. Lachance reported he also saw 1 suspected case in the spring of 2004, who was lost to follow-up, and another in the fall of 2005, who is a current patient but is not included in these findings. However, none of these individuals has been confirmed with the condition.

Treatment of these patients, said Dr. Lachance, was determined by symptom severity. More severely affected individuals received either high-dose methylprednisolone or intravenous immunoglobulin on a continuing schedule. Individuals less severely affected were treated with analgesics and/or gabapentin.

"As far as we know there have been no new cases since the brain-harvesting procedure was terminated in December. But I want to emphasize that it is still early, and it's possible more cases could emerge over the coming months. It's important to note that this is an ongoing investigation, and the story could very well change," said Dr. Lachance.

American Academy of Neurology 60th Annual Meeting: Abstract LBS.001. Presented April 16, 2008.

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