Novel H1N1 (referred to as “swine flu” earlier) is a new influenza virus causing illness in humans. This virus was first detected in people in Mexico and the United States in April 2009. It is spreading worldwide from person-to-person, probably in much the same way as the spread of regular seasonal influenza. The latter can be associated with neurologic complications,1,2 but the frequency with which these occur with the novel influenza A(H1N1) virus infection is unknown. Neurologic sequelae such as seizures, encephalopathy, or encephalitis within 5 days of the initial illness were reported in 4 children with H1N1 infection for the first time in Dallas, Texas.3 Brain imaging findings were normal in these children.
The first case of neuroimaging abnormalities in H1N1 infection was reported in a child from Texas presenting with imaging features of acute necrotizing encephalitis.4 Subsequently, 2 more cases of encephalitis associated with H1N1 infection have been reported by Haktanir from Turkey5 and Ormitti et al from Italy.6 Neuroimaging findings in influenza-associated encephalopathy might be normal, but in severe cases, abnormalities can include diffuse cerebral edema and bilateral thalamic lesions.2 Lack of evidence of H1N1 viral infection in the CSF suggests that neurologic manifestations might be an indirect effect of respiratory tract infection, similar to the ones observed in influenza A and B viral infections.1,2
The imaging findings may resemble those of acute necrotizing encephalitis or may present as encephalitis with hemorrhage and typically involve the bilateral thalami as seen in all 3 case studies.4–8 These imaging features have also been described in Arbovirus encephalitis and may overlap these conditions.9 These case studies suggest that imaging may be abnormal in H1N1-associated encephalitis with normal CSF; and in the presence of flu-like symptoms in the endemic zones, H1N1-associated encephalitis should be considered as an important differential diagnosis. Because these patients are known to recover completely with treatment, early recognition of H1N1-associated encephalitis will result in early institution of therapy specific to H1N1 and will possibly help in reducing the associated morbidity and mortality.
References
- 1.
- 2.
- 3.
- 4.
- 5.
- 6.
- 7.
- 8.
- 9.
- Copyright © American Society of Neuroradiology