Mysterious ‘sleeping sickness’ pandemic offers insight into Parkinson’s
A bizarre disease that caused sufferers to fall into a deep ‘sleep’ while still being aware of their surroundings can offer us insight into the nature of Parkinson’s disease, says an expert on the history of brain disease.
Dr Paul Foley, from Neuroscience Research Australia, says the pandemic of encephalitis lethargica, which swept the world in the 1920s, caused Parkinson’s-like symptoms in many sufferers, most of whom were less than 30 years old.
“While we don’t know for sure what caused encephalitis lethargica, there is strong evidence that it was a virus that ultimately caused neurological symptoms appearing many years after the initial infection,” says Dr Foley.
“We can use this as a model to investigate the notion that there may be an infectious involvement in other brain diseases, such as Parkinson’s disease, and even Alzheimer’s disease and multiple sclerosis,” he says.
Encephalitis lethargica was most prominent between the two World Wars. It was first described in 1917, with the most extensive outbreak occurring throughout the Northern Hemisphere in 1920-21, and a final major epidemic in the United Kingdom in 1924.
“New cases were regularly reported until the 1930s, but after this time it effectively disappeared, although scattered cases were seen from time to time,” says Dr Foley.
The disorder had two distinct phases. During the first, acute phase, victims seemed to fall into a deep sleep, but often maintained an awareness of their environment.
“They would close their eyes, and just didn’t have the will power to move themselves. But they could recount afterwards what the doctors around them were saying, what the nurses were doing,” says Dr Foley.
As many as one third of sufferers died during this initial phase.
In the second, chronic phase, which often commenced after a relatively healthy interval of many years, most victims developed incurable neurological symptoms resembling Parkinson’s disease, resulting in life-long incapacity. Encephalitis lethargica is best known today through the depiction of these cases in Oliver Sacks’ book, ‘Awakenings’.
Dr Foley says encephalitis lethargica can be most accurately described as a ‘neuro-psychiatric’ disorder, as victims also developed psychiatric symptoms.
“In adults, this typically involved a reduced ability to exercise their will, while a minority developed syndromes resembling schizophrenia. Children developed a syndrome that resembled what is now called ‘attention deficit/hyperactivity disorder’,” he says.
Dr Foley says his research indicates that around 30% of those who developed chronic symptoms did not experience any acute phase symptoms.
“This suggests that it is possible that an infection can have long term consequences for brain function, even where the initial infection is mild or even negligible,” he says.
Dr Foley says that encephalitis lethargica can help us investigate other infections that cause neurological symptoms after a long lag time, and can possibly help us understand the cause of some brain diseases.
“The idea of an infectious involvement in diseases like schizophrenia, Alzheimer’s disease and Parkinson’s disease is controversial today, just as it was in the 1920s,” he says.
“But by the end of the 1920s, researchers and clinicians had built up a body of evidence with regards to encephalitis lethargica, which showed an infection can have both serious psychiatric and neurological outcomes.”
“I’m hoping that putting these facts out there may help researchers piece together the puzzle with regards to other brain diseases,” says Dr Foley.
Dr Foley is currently completing a book on encephalitis lethargica.