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Infectious, noninfectious etiologies should be considered in diagnosis of temporal lobe encephalitis
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In making the differential diagnosis of temporal lobe encephalitis, it is important to consider potential infectious and noninfectious etiologies in addition to the herpes simplex virus, according to recent findings published in Clinical Infectious Diseases.
“Herpes simplex encephalitis (HSE) … is commonly associated with temporal lobe abnormalities on neuroimaging,” the researchers wrote. “However, mimics of HSE, including other infections and increasingly recognized autoimmune causes, have been described in cases of temporal lobe encephalitis.”
Researchers reviewed 2,001 cases of adult encephalitis from the California Encephalitis Project with temporal lobe abnormalities detected on MRI. Patients who met the case definition for encephalitis underwent testing for herpes simplex virus (HSV)-1 and HSV-2, varicella zoster virus (VZV), Epstein-Barr virus (EBV), HHV-6, West Nile virus and respiratory pathogens, including influenza viruses, respiratory syncytial virus and adenoviruses. The researchers identified noninfectious etiologies based on medical records and communication with referring physicians. Medical records and case history forms were used to assess demographics, clinical presentation, laboratory data and brain MRI characteristics.
The researchers studied the correlations between specific clinical and MRI characteristics and HSE vs. other temporal lobe encephalitis etiologies, as well as the radiologic predictors of HSE.
Of the 251 cases determined to be temporal lobe encephalitis, infectious etiology was present in 43%, while 16% had a noninfectious etiology. Of the infectious cases, HSV was the most prevalent agent of infection (n = 60), with tuberculosis accounting for eight cases and VZV present in seven. Of cases with noninfectious etiology, more than half (n = 21) were attributable to autoimmune disease. HSE etiology was associated with older age (56.8 vs. 50.2 years), white race (53% vs. 35%), presenting acutely (88% vs. 64%) and presenting with fever (80% vs. 49%). HSE cases were less likely to present with a rash (2% vs. 15%).
Multivariate logistic regression analysis revealed a lower likelihood of HSE associated with bilateral temporal lobe involvement (OR = 0.38, 95% CI, 0.18-0.79) and lesions outside the temporal lobe, insula or cingulate (OR = 0.37, 95% CI, 0.18-0.74).
“Use of these imaging characteristics, in combination with the clinical history, epidemiologic risk factors and laboratory testing, may improve our ability to differentiate between etiologies of [temporal lobe] encephalitis,” the researchers wrote. “Possible next steps include assessing the performance of these MRI characteristics in an unselected prospective cohort to determine their predictive value and evaluating MRI characteristics on serial brain imaging … to identify features that may enhance our ability to distinguish HSE from other causes of [temporal lobe] encephalitis.” – by Jen Byrne
Disclosure: The researchers report no relevant financial disclosures.
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