The spectrum of acute encephalopathy with reduced diffusion in the unilateral hemisphere.

We describe the clinical, EEG, and MRI features of children with reduced diffusion in the unilateral hemispheres. Seven patients with reduced diffusion in the subcortical white matter of the unilateral hemisphere alone were identified. Their median age was 32 months. Human herpesvirus 6 infection was virologically proven in 2 patients and human herpesvirus 7 in 1. The initial neurological symptom was a prolonged seizure in 4, a brief seizure in 2, and delirious behavior in 1. Three patients had biphasic clinical course. Laboratory tests were unremarkable in most patients. MRI showed no abnormal findings during the acute phase, whereas reduced diffusivity in the unilateral hemisphere was seen during the subacute phase. EEG during the acute phase demonstrated marked slowing in the affected hemisphere in 1 patient, mild slowing in 4, and relatively low voltage in 1. No patients died, but 6 patients had various degrees of neurological sequelae. Acute encephalopathy with reduced diffusion in the unilateral hemisphere may be one of the representative phenotypes of acute encephalopathy.