New research shows that the occurrence of narcolepsy in China is highly correlated to a seasonal pattern, with onset most frequent in April. A significant increase in narcolepsy cases was also observed following the 2009-2010 H1N1 pandemic, but the findings now available in Annals of Neurology, a journal of the American Neurological Association and the Child Neurology Society, report flu vaccination was unlikely to be the cause of the increase.
Medical evidence shows that narcolepsy-cataplexy affects less than 1% of the world population and NINDS estimates 1 in 3,000 Americans have this disorder. Following the 2009-2010 H1N1 pandemic, studies reported increased incidence in narcolepsy and increased risk of narcolepsy in patients receiving the Pandemrix vaccine. Other studies show that infection with streptococcus preceded the onset of narcolepsy in Caucasian patients, suggesting upper airway infections may trigger the disorder.
For the present study, the research team, led by Dr Fang Han from the Beijing University People’s Hospital in China and Dr Emmanuel Mignot with the Stanford Center for Sleep Sciences and Medicine in Palo Alto, Calif, conducted retrospective analysis of narcolepsy onset in patients diagnosed between 1998 and 2011 in Beijing. Data on the month and year of narcolepsy onset was collected from 629 patients (86% children) who were part of the Stanford-Beijing University Chinese narcolepsy study cohort. A vaccination history was provided by 182 participants who developed narcolepsy after October 2009.
“Our findings show a seasonal variation in narcolepsy onset in a Chinese population, occurring most frequently in late spring and early summer,” said Han. Analysis revealed that onset of narcolepsy was least frequent in November and occurred most often in April, with close to a sevenfold increase from lowest point to peak time.
Researchers also studied year-to-year variations, identifying 173 cases of narcolepsy following the 2009-2010 H1N1 flu pandemic, which represented a threefold increase in the disorder. “The increase in narcolepsy incidence was unlikely caused by increased vaccination as only 6% of study narcolepsy participants reported receiving a vaccination against H1N1,” noted Mignot. A 5- to 7-month delay between the seasonal peak in flu and peak in the onset of narcolepsy was also observed.
"These findings are reminiscent of the encephalitis lethargica epidemic that followed the great Spanish influenza pandemic of 1917-1918. 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," Mignot concluded.