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When the body attacks the brain: Immune system often to blame for encephalitis, study finds
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ROCHESTER, Minn. — Encephalitis caused by the immune system attacking the brain is similar in frequency to encephalitis from infections, Mayo Clinic researchers report in Annals of Neurology.
Encephalitis is a term used to describe brain inflammation. Its symptoms include fever, confusion, memory loss, psychosis and seizures. It progresses quickly over days to weeks and can be life-threatening. Traditionally, it has been thought that infections account for most cases of encephalitis, but this study shows autoimmune encephalitis is an equally common cause.
“The results of our study suggest that doctors evaluating patients with encephalitis should search for autoimmune causes in addition to infectious causes, given both have a similar frequency,” says Eoin Flanagan, M.B., B.Ch., senior author of the population-based study and an autoimmune neurology specialist at Mayo Clinic.
Feb. 22 is World Encephalitis Day — a day to raise awareness of the illness.
Infection remains an important concern when evaluating patients with encephalitis, notes Michel Toledano, M.D., one of the study’s co-investigators and a neuro-infectious diseases specialist. “But the results of our study indicate that doctors also should explore autoimmune causes to ensure that the appropriate treatment is given, which is essential to prevent long-lasting damage,” Dr. Toledano says.
To identify cases of encephalitis, the study used data from the Rochester Epidemiology Project, a medical records database of all medical providers in Olmsted County, Minnesota. The researchers found about 14 per 100,000 people had autoimmune encephalitis in their lifetime, compared to 12 per 100,000 who had infectious encephalitis. One study limitation is that the diagnostic criteria for autoimmune and infectious causes of encephalitis differed, which could affect the comparison.
“Previously, we did not know how common autoimmune encephalitis was, as no prior studies evaluated this,” Dr. Flanagan says. “This study allows us to estimate that approximately 1 million people worldwide had autoimmune encephalitis in their lifetime. We also estimate that, currently, about 90,000 people around the world develop autoimmune encephalitis each year.”
In this study, the researchers used 2016 diagnostic criteria for autoimmune encephalitis. Using the Mayo Clinic Neuroimmunology Laboratory, which performs comprehensive neural autoantibody testing on blood and spinal fluid, the researchers were able to identify neural antibody markers that indicate a likely autoimmune cause.
“Our study showed that clinicians are now detecting more cases of autoimmune encephalitis than they were in the past because of the discovery of these new neural autoantibody markers. These advances in diagnostic testing are good news for patients, as they have allowed doctors to diagnose and treat autoimmune encephalitis more effectively.” Dr. Flanagan says.
This research was supported by the National Institute on Aging grant R01AG034676 through the Rochester Epidemiology Project and the National Institute of Neurological Disorders and Stroke grant NS065829
Additional researchers involved in the Mayo Clinic study were Divyanshu Dubey, M.B.B.S.; Sean Pittock, M.D.; Cecilia Kelly, M.D.; Andrew McKeon, M.B., B.Ch.; Alfonso Lopez Chiriboga, M.D.; Vanda Lennon, M.D., Ph.D.; Avi Gadoth, M.D., Tel Aviv Sourasky Medical Center; Carin Smith, Sandra Bryant, Christopher Klein, M.D.; Allen Aksamit, M.D.; Bradley Boeve, M.D.; and Jan-Mendelt Tillema, M.D.
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About the Rochester Epidemiology Project
The Rochester Epidemiology Project is a collaboration of clinics, hospitals, and other medical and dental care facilities in southern Minnesota and western Wisconsin. It was founded by Mayo Clinic and Olmsted Medical Center in 1966 in Olmsted County, Minnesota. The collaboration now includes Olmsted County Public Health Services as its first public health member and stretches across 27 counties. This collaboration and sharing of medical information makes this area of Minnesota and Wisconsin one of the few places where true population-based research can be accomplished. Learn more about the Rochester Epidemiology Project.
About Mayo Clinic
Mayo Clinic is a nonprofit organization committed to clinical practice, education and research, providing expert, comprehensive care to everyone who needs healing. Learn more about Mayo Clinic. Visit the Mayo Clinic News Network.
Media contact:
- Susan Barber Lindquist, Mayo Clinic Public Affairs, 507-284-5005, newsbureau@mayo.edu
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