Subacute sclerosing panencephalitis (SSPE) occurs several years after the initial measles infection. It begins with behaviour changes before progressing to severe seizures. SSPE is always fatal.
The condition is rare and, because of the long time lag between measles infection and the development of SSPE, is has proven difficult to study.
A new analysis of 17 cases of by the University of California – mostly related to a California measles epidemic from 1988-1990 – suggests the rate could be as high as one in 600, depending on the patient’s age at the time of infection.
The findings were reported at a conference in the US and have yet to be published in a peer-review journal but sparked renewed interest in the devastating condition.
“We used to think it was quite rare,” said Dr James Cherry until a study from German researchers in 2013 suggested the rate was about one in 1,700 measles infections among children under age five. The “really striking” findings of the current study suggest that is still an underestimate, he said.
First year of life
Many of those affected by SSPE were infected by measles in the first year of life, before the live attenuated vaccine can be given, Cherry and colleagues found.
“We need to be thinking about herd immunity,” he said, because what protects those infants too young to be vaccinated is making sure that everyone around them is immune to the disease.
The study is based on data mainly from the now-defunct California Encephalitis Project, which investigated encephalitis cases of all types in the state starting in 1998.
They found that 9,564 children younger than the age of five had measles in the outbreak, including seven SSPE cases that were recorded at the time. The numbers suggest the risk of developing SSPE after measles infection is 1 in 1,367.
However, of the 3,651 children who were less than one year old when they caught measles, six later developed SSPE. This implies a rate of 1 SSPE case in every 609 recorded measles infections.
View our most-read article ever: How measles can change a life