February 20, 2018
2 min read

Infectious, autoimmune encephalitis show similar incidence, prevalence

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Findings recently published in Annals of Neurology indicate that autoimmune encephalitis has an incidence and prevalence similar to that of infectious encephalitis.

“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,” Eoin P. Flanagan, MB, BCh, autoimmune neurology specialist at the Mayo Clinic, said in a press release.

Flanagan and colleagues conducted a population-based comparative study evaluating the incidence and prevalence of both infectious and autoimmune encephalitis among patients in Olmsted County, Minnesota. They used 2016 diagnostic criteria to diagnose autoimmune encephalitis and required the confirmation of an infectious pathogen for the diagnosis of infectious encephalitis. The researchers calculated the prevalence and incidence rates of each, adjusting for age and sex. The researchers excluded patients with an uncertain etiology.

The prevalence of autoimmune encephalitis was 13.7 per 100,000, compared with 11.6 per 100,000 for infectious encephalitis, Flanagan and colleagues reported (P = .63). A viral subcategory showed a prevalence of 8.3 per 100,000 (P = .17).

Between 1995 and 2015, autoimmune encephalitis had an incidence rate of 0.8 per 100,000 person-years, whereas infectious encephalitis demonstrated an incidence rate of 1 per 100,000 person-years, the researchers wrote (P = .58). Patients with autoimmune encephalitis experienced more relapses or hospital readmissions than those with infectious disease (P = .03).

Further, incidence of autoimmune encephalitis rose during the study period, increasing from 0.4 per 100,000 person-years between 1995 and 2005 to 1.2 per 100,000 person-years between 2006 and 2015, the researchers reported. Flanagan and colleagues attributed this increase to an increase in the detection of autoantibody-positive cases.

Black patients demonstrated a greater incidence of autoimmune encephalitis than white patients, the researchers wrote (2.7 vs. 0.7 per 100,000 person-years; P = .01), as well as a greater prevalence (38.3 vs. 13.7 per 100,000; P = .04).

Myelin oligodendrocyte glycoprotein and glutamic acid decarboxylase 65 were the most common neural antibodies (1.9 per 100,000 for both), followed by unclassified neural antibodies (1.4 per 100,000); leucine-rich glioma-inactivated protein 1 (0.7 per 100,000); collapsing response-mediator protein 5 (0.7 per 100,000); N-methyl-D-aspartate receptor (0.6 per 100,000); antineuronal nuclear antibody type 2 (0.6 per 100,000); and glial fibrillary acidic protein A (0.6 per 100,000), according to Flanagan and colleagues.

“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 antibody markers,” the researchers wrote. “These advances in diagnostic testing are good news for patients, as they have allowed doctors to diagnose and treat autoimmune encephalitis more effectively.” – by Andy Polhamus

Disclosures: The authors report no relevant financial disclosures.