An infant with encephalitis

Abstract

This boy had an underlying hypogammaglobulinaemia and a chronic, progressive neurological disease secondary to poliovirus vaccination. Poliovirus-vaccine-associated paralytic disease is a known complication of live poliovirus vaccination, with an overall occurrence rate of 1 case per 2·6 million doses distributed in the USA. Affected patients usually develop paralytic poliomyelitis, with acute onset of asymmetrical limb weakness, which progresses to reach maximum severity within 2 weeks, followed by variable degree of recovery. The risk is greatly increased in children with hypogammaglobulinaemia, in whom the presentation might be atypical. Signs of encephalitis such as altered consciousness level and muscle tone, seizures, and developmental regression are the predominant features. In a previous report, these presentations were associated with viral replication in the central nervous system with extensive gliosis and necrosis of the brain especially the thalamus and basal ganglia. The mechanism relating hypogammaglobulinaemia to the predominant cortex rather than anterior horn cell involvement is, however, not known. In developed countries, the emergence of vaccine-associated poliomyelitis has become a concern since the successful eradication of the naturally acquired disease by widespread immunisation with oral Sabin poliovirus vaccine. Our case should serve to remind clinicians that in the management of a child with unexplained encephalitis, investigations for hypogammaglobulinaemia and evidence of poliovirus infection should be considered. Siblings should undergo thorough perinatal screening and live vaccine might better be replaced by killed vaccine.