The report includes the detailed results of the diagnostic assessment and clinical care of these patients, a description of some of the scientific investigations performed to try to understand the nature of the illness, as well as Mayo Clinic’s involvement with components of the public health investigation.
Since late 2007, Mayo Clinic has provided comprehensive care and specialized diagnostic services for 24 individuals who first complained of neurological symptoms such as weakness, fatigue, pain, difficulty walking, tingling in the arms and legs, severe headache, and in one case, progressive confusion and seizures. The individuals all worked at Minnesota or Indiana pork processing plants in or near the area where compressed air was used to extract brain matter. Extensive investigations, in collaboration with the Minnesota Department of Health and the U.S. Centers for Disease Control and Prevention, suggested that this novel illness was an autoimmune neurological disorder caused directly by exposure to aerosolized brain matter. The most frequent effect of the auto immune system disorder in these patients was inflammation of peripheral nerves in a very distinct pattern (a sensory predominant polyradiculoneuropathy).
The collective assessment of a number of test results led the Mayo team to their conclusions, but the most compelling results came from the Mayo Clinic Neuroimmunology Laboratory. “Blood samples for each of the 24 affected patients were found to have antibodies that reacted when exposed to neural tissue,” says Daniel Lachance, M.D., a Mayo Clinic neurologist and the lead author of this paper. “This finding was new and specific to this outbreak.”
The Mayo Clinic publication reports that, as part of the public health investigation, the Minnesota Department of Health collected blood samples from 90 other individuals who worked at the Minnesota pork processing plant who appeared well and had no neurologic symptoms.
Testing these samples in the Mayo Clinic Neuroimmunology Lab demonstrated that the same antibody response to the brain matter exposure that occurred in affected workers also occurred in 34 percent of the asymptomatic individuals. According to Dr. Lachance, these findings suggest that the body’s immune response in the workers was most likely the result of exposure to aerosolized brain matter. However, there are other unknown factors which caused some individuals to become ill as a result of the exposure, while others remained healthy. The Mayo Clinic team made an additional important observation. “The antibody levels seemed to correlate directly with the distance between the point of exposure where the aerosolized brain matter was produced and the primary place in the production line at the plant where each individual worked,” says Dr. Lachance. “Not surprisingly, the closer an individual worked to the point of exposure, the higher their antibody levels.”
According to P. James B. Dyck, M.D., a Mayo Clinic neurologist and an author of this paper, the aerosolized brain tissue is a conglomeration of brain material with many components that can cause immune systems to react. He says that the antibody response is to multiple different components of the nervous system.
Another compelling piece of evidence that this was a unique disease due to occupational exposure was the distinctive patterns found on nerve conduction studies. The involved regions were the very terminal ends of the nerves and the beginning regions of the nerves (nerve roots) as they exited the spinal cord. “These patterns of nerve conduction abnormalities were very unusual and were one of the first observations that made us believe we had an outbreak,” says Dr. Dyck. “This is an important observation as these nerve regions are where the blood nerve barrier (the defense of the nerve) is the weakest and hence the parts of the nerve most susceptible to autoimmune attack.”
Mayo Clinic physicians continue to follow most of the affected patients, and their publication in Lancet Neurology reports consistent improvement in these individuals. “In ongoing patient follow-up we’ve found that all objective measures, including physical examination findings, MRI, electrical and physiological abnormalities, are all improving over time,” says Dr. Dyck. “Additionally, as we’ve measured the antibody levels over time, we’ve found that all levels have fallen, and in most instances have nearly normalized.”
Other Mayo Clinic scientists involved in this research include Vanda Lennon, M.D., Ph.D., director of the Mayo Neuroimmunology Laboratory; Sean Pittock, M.D., the lab’s co-director; Jennifer Tracy, M.D.; Karl Krecke, M.D.; Kimberly Amrami, M.D.; Eric Poeschla, M.D.; Robert Orenstein, D.O.; and Bernd Scheithauer, M.D. James Sejvar, M.D., and Stacy Holzbauer, both from the Centers for Disease Control and Prevention, and Aaron DeVries, M.D., Minnesota Department of Health, also contributed to this research.
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Mayo Clinic is the first and largest integrated, not-for-profit group practice in the world. Doctors from every medical specialty work together to care for patients, joined by common systems and a philosophy of “the needs of the patient come first.” More than 3,700 physicians, scientists and researchers, and 50,100 allied health staff work at Mayo Clinic, which has campuses in Rochester, Minn; Jacksonville, Fla; and Scottsdale/Phoenix, Ariz.; and community-based providers in more than 70 locations in southern Minnesota., western Wisconsin and northeast Iowa. These locations treat more than half a million people each year. To obtain the latest news releases from Mayo Clinic, go to www.mayoclinic.org/news. For information about research and education, visit www.mayo.edu. MayoClinic.com (www.mayoclinic.com) is available as a resource for your health stories.