Narcolepsy increase in China after H1N1 outbreak, not vaccine-related
MedWire News: Narcolepsy onset appears to be seasonal in China, peaking after upper airway infection outbreaks such as the 2009 H1N1 winter flu pandemic, say researchers.
However, they add that contrary to previous suggestions, there appears to be no link between the H1N1 vaccination and narcolepsy.
Narcolepsy is a rare neurological sleep disorder caused by the loss of hypocretin/orexin neurons in the hypothalamus, which is thought to be the result of an autoimmune process.
Recent reports of increased prevalence of narcolepsy following the H1N1 flu vaccination in Northern Europe have caused concern.
To investigate whether the vaccination increased narcolepsy risk in China and to further explore factors associated with onset of the condition, Emmanuel Mignot (Stanford Center for Sleep Sciences and Medicine, Palo Alto, California, USA) and colleagues carried out a retrospective analysis of narcolepsy onset in Beijing, China, between 1998 and 2010.
In total, the researchers collected self-reported month and year of onset from 629 patients (86% children). Associations with the H1N1 vaccine were evaluated in 182 patients who developed the condition after October 2009.
As reported in the Annals of Neurology, the team found that narcolepsy onset was seasonal, with an average 6.7-fold more patients developing the condition in April compared with November in each year of the study. This corresponds with a 5-7 month delay between the peak of the winter upper respiratory infections and narcolepsy onset on a year-to-year basis.
When the researchers looked at variation in the annual prevalence of narcolepsy, they noticed a three-fold increase in the onset of narcolepsy after the 2009 H1N1 winter flu pandemic.
This increase is unlikely to be related to vaccination, however, as only 8 of the 142 patients who developed the condition after the pandemic reported having the vaccination.
The researchers say that despite the limitations of the study, due to its observational nature, the results suggest that H1N1 or other winter infections are causally associated with the onset of narcolepsy.
"These findings are reminiscent of the encephalitis lethargica epidemic that followed the great Spanish influenza pandemic of 1917-1918," commented Mignot.
"Not only narcolepsy, but also psychosis and Parkinson's disease may follow winter infections, and further research is needed in the area of autoimmune diseases of the brain," he concluded.
By Helen Albert