The neural complications of influenza are shown in box 1. The commonest of these, particularly in young children from Japan and Taiwan, is influenza virus associated encephalopathy. Influenza virus associated encephalopathy is an acute non-inflammatory encephalopathy that presents with seizures and coma on the day, or the day after, influenza symptoms start.¹ Influenza is characterised by the abrupt onset of a fever greater than 39°C, respiratory symptoms (rhinorrhoea, cough, and sore throat), myalgia (particularly of the back and limb muscles), and headache.² In infants symptoms are often lethargy, poor feeding, apnoea, and interstitial pneumonia; older children may also have less specific symptoms of croup, otitis media, diarrhoea, and vomiting.

INFLUENZA VIRUS ASSOCIATED ENCEPHALOPATHY

Influenza virus associated encephalopathy is a disease of young children with a peak incidence between 6 and 18 months of age.¹ It has mostly been reported from Japan and Taiwan, but cases have been reported from Europe and North America and in Caucasian children.³ It is a severe disorder with a fatality of around 30%, and persisting neurodisability in around one third of survivors, associated with cerebral atrophy. The majority of cases complicate influenza A infections, but influenza B is responsible for around 10%.

Rapidly progressive neurological deterioration, seizures, and coma occur around 26 hours after the onset of influenza symptoms. Neuroimaging shows cerebral oedema in the …