• Written By: Mike Vaphiades, DO

    The authors report in the March issue of the Journal of Neuro-Ophthalmology an unusual case of H1N1 influenza A virus infection primarily affecting the posterior visual pathways. The patient, a 20-year-old woman, developed bilateral cortical visual loss. The authors describe H1N1 encephalopathy, the associated neuroimaging abnormalities and related syndromes.

    The patient was infected with the 2009 H1N1 strain of influenza A. Brain MRI showed restricted diffusion of the parietal and occipital lobes. Her spinal fluid did not contain inflammatory cells.

    The authors note that neuroimaging abnormalities associated with the pandemic 2009 H1N1 strain have been reported infrequently, usually in children. Neuroimaging abnormalities from influenza A encephalitis may be due to several mechanisms. Hypoxic or anoxic damage as a result of respiratory dysfunction can lead to CNS ischemia or infarction. Alternatively, CNS damage may be due to a direct infectious or parainfectious process related to the H1N1 virus.

    They conclude that the pattern of symmetrical MRI abnormalities with restricted diffusion in their patient most likely represents a parainfectious encephalopathy. They say that her elevated protein level but otherwise unremarkable cerebrospinal fluid (CSF) level is consistent with the CSF profile of other H1N1 encephalopathy patients.