Pandemic influenza A-associated acute necrotizing encephalopathy without neurologic sequelae.

We describe an 8-year-old girl with the mildest form of acute necrotizing encephalopathy, associated with pandemic influenza A. She manifested a convulsion engendering deterioration of consciousness, although cranial computed tomography and magnetic resonance imaging within 4 hours after the convulsion revealed no abnormalities. Cranial magnetic resonance imaging 20 hours after the convulsion revealed lesions of the thalamus bilaterally, brainstem tegmentum, internal capsule, and white matter. She was diagnosed with acute necrotizing encephalopathy. Typically, the prognosis of acute necrotizing encephalopathy with a brainstem lesion is poor. Nevertheless, she recovered almost completely, after early intervention with pulsed methylprednisolone and high-dose γ-globulin therapy. She manifested a thermolabile phenotype of carnitine palmitoyltransferase II variants such as cystine-isoleucine-methionine phenotype type 9 (FVM-CIM; Phe352Cys-Val388Ile-Met647Met alleles), resulting in a predisposition to encephalopathy during influenza infection. This case is the first, to the best of our knowledge, of pandemic influenza A-associated acute necrotizing encephalopathy with a good outcome despite severe magnetic resonance imaging findings.