Abstract & Commentary
Neurological Manifestations of Influenza in the Era of the new Pandemic (H1N1) Strain
By Dean L. Winslow, MD, FACP, FIDSA
Clinical Professor of Medicine and Pediatrics Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Associate Editor of Infectious Disease Alert
Dr. Winslow is a consultant for Siemens Diagnostic.
SYNOPSIS: 25 cases of neurologic complications of influenza were reported from Great Britain beginning in 2011. 84% of cases were seen in children. A variety of distinct neurological manifestations were seen. 80% of patients required intensive care, 68% had poor outcomes, and 4 patients (16%) died.
SOURCE: Goenka A, et al. Neurological manifestations of influenza infection in children and adults: results of a national British surveillance study. CID 2014; 58: 775-84.
A 2-year surveillance study was conducted in British neurological surveillance units beginning in 2011. 21 children and 4 adults with influenza virus infection were identified. PCR of respiratory samples identified influenza A in 21 patients (of which 20 were H1N1) and influenza B in 4 patients. 12 children had encephalopathy (1 with movement disorder), 8 encephalitis, and 1 meningoencephalitis. Two adults had encephalopathy with movement disorder, 1 encephalitis, and 1 had Guillain-Barre syndrome. Specific acute encephalopathy syndromes included 4 with acute necrotizing encephalopathy, 1 acute infantile encephalopathy affecting frontal lobes, and 1 acute hemorrhagic leukoencephalopathy. 80% of patients required intensive care, 68% had poor neurologic outcomes, and 16% died.
This is a very interesting study from the UK, which presents detailed evaluations of 25 cases of well-documented influenza-associated neurologic complications. The authors very carefully evaluated the specific neurologic manifestations observed clinically and in most cases were able to correlate these with neuro imaging studies including MRI scans. In contrast to the large study of influenza-associated neurologic complications published by Glaser et al1 in 2012 (which reported on 77 such patients with neurologic complications associated with pandemic H1N1 in California who became ill during the 2009-2010 season and tended to have good outcomes), this British study seemed to show much more severe disease and worse neurologic outcomes. However, as was the case in the study by Glaser and colleagues, neurologic complications were seen primarily in children.
It seems clear that influenza A H1N1 strains circulating since 2009, in particular, appear to be more neurovirulent than influenza strains circulating in previous years. In the Glaser paper influenza-associated neurologic complications were seen in 4% of cases of fatal or severe 2009 H1N1 influenza. Sadly, most of these cases were potentially preventable. In the British surveillance study, none of the patients reported had received influenza vaccine. The pathogenesis of this apparent increased neurovirulence is not known.
- Glaser CA, et al. A population-based study of neurologic manifestations of severe influenza A (H1N1) pdm09 in California. Clin Infect Dis 2012; 55: 514-20.