Probable post-influenza cerebellitis.

The nucleoprotein (NP) gene of type B influenza virus was detected by reverse transcription polymerase chain reaction (RT-PCR) from the cerebrospinal fluid (CSF) of a patient presenting with ataxia due to cerebellitis. The CSF was obtained 7 and 9 weeks after flu syndrome occurred, suggesting persistence of viral genes in the central nervous system (CNS). Although an unusually high serum hemagglutination inhibition (HI) titer against influenza virus B was noted, HI titers of the CSF were not elevated.