Clinical and radiological variability of influenza-related encephalopathy or encephalitis

Influenza-related encephalopathy or encephalitis is not rare in children. However, it is not well understood why the brain lesion develops from influenza infection. The purpose of this study was to clarify its pathogenesis by analyzing the clinical and neuroradiological findings in patients having influenza-related brain lesions.

The clinical findings in 10 children with influenza-related brain lesions were analyzed. Eight patients had findings consistent with the diagnosis of acute encephalopathy and two had postinfectious focal encephalitis.

The results from magnetic resonance imaging (MRI) or computed tomography were divided into five categories: normal (category 1); diffuse involvement of the cerebral cortex (category 2); diffuse brain edema (category 3); symmetrical involvement of the thalamus (category 4); and postinfectious focal encephalitis (category 5). Patients in categories 2-4 had symmetrical or diffuse brain lesions without leukocytosis in their cerebrospinal fluid, and there were no inflammatory reactions in the brains of two autopsied patients. Furthermore, serum concentrations of GOT were high in all, and disseminated intervascular coagulation was present in 4 of 5.

These findings suggested that the pathogenesis of the brain lesions in these cases was toxic or metabolic damage due to multisystemic organ diseases induced by the influenza virus. The MRI findings in patients in category 2 suggested diffuse cortical cell necrosis. On the other hand, the thalamic lesions in category 4 patients reflected hyperpermeability of the blood vessels followed by severe edema with or without microhemorrhages. The pathogenesis of lesions of category 5 included allergic angitis of a self-limiting nature. These findings indicated that the pathogenesis of brain damage induced by influenza infection was very variable.