This terrifying disease started in World War I Europe

Encephalitis lethargica is a disease that seems to belong in a horror movie, complete with brain damage that causes victims to sleep for years or to hack away at their own bodies — and it all started in Europe during World War I.

It was first described by World War I pilot and noble, Constantin von Economo, who switched to a career in medicine at the request of his parents after family members died in the war. As a physician, he served both civilians and the Central Powers, and his historical significance comes from being the first to describe a neurological disorder that popped up during the war.

His first patients reported constant exhaustion despite constantly sleeping, leading some people to call it the "sleeping disease" or "sleepy sickness." This wasn't exactly correct, though, as many patients never truly slept. They remained aware of their surroundings even when seemingly in deep sleep. As the disease progressed, patients also began exhibiting symptoms like abnormal eye movement, delirium, headache, or paralysis.

The paralysis and other symptoms were sometimes limited to one side of the body, giving off the surreal result that one side of the face and body became sluggish and tired while the other side remained relatively alert and functional.

From here, patients' symptoms would progress in a couple directions. 5 million people were afflicted with the disease from 1917 to 1928. Approximately a third died, a third survived, and the final third were trapped in endless sleep. But the scary part for survivors was that symptoms could return years later — or they could suffer from Parkinson's brought on by the disease.

Dr. Oliver Sacks, a physician famous for his work with encephalitis lethargica patients who slept for decades before awaking for a short period.

(Luigi Novi, CC BY 3.0)

And that endless sleep thing wasn't a euphemism or anything. Some patients went to sleep for decades, only coming out of their near-endless rest when given an anti-Parkinson's medication in 1969 through an effort led by Dr. Oliver Sacks. Unfortunately, Sack's treatment with L-DOPA only provided a temporary relief of their symptoms. All patients eventually regressed back to permanent sleep or a catatonic state.

Oddly enough, those afflicted with long-term catatonia did get one benefit: They aged much more slowly than people awake.

But while encephelitis lethargica has plenty of terrifying traits for adults, it was much worse in children and adolescents, among whom it caused psychosis. In one extreme case, a young girl pulled out many of her teeth and gouged out both of her eyes. Patients also often inflicted serious violence, sexual and otherwise, against others with no regard for age, gender, or nearly any other factor.

People attacked members of their own family, authority figures, or random passersby, often with little visible emotion afterwards.

Encepheilitis lethargica could strike people of any age, and it often caused long-term Parkinson's in the months or years after a patient had seemingly recovered from the condition.

(British Medical Journal 1925, Gullan)

Obviously, for troops in the war and returning veterans, the idea that exhaustion could be a sign of their imminent demise was terrifying, and the fact that their families could be afflicted by this mysterious disease was terrifying, but another outbreak pushed the sleepy sickness to the back of most people's minds.

The Spanish flu pandemic broke out in 1918 and eventually killed between 20 and 50 million victims of the roughly 500 million people affected.

Today, we still don't know the cause of encephelitis lethargica, but new cases fortunately fell off a cliff in 1926 and continued to dwindle in the 1930s. Now, new cases are extremely rare, but the exact symptoms of encephelitis lethargica were so varied that it's hard to even be sure that new cases are from the same cause.

The title page of Constantin von Economo's 1931 description of encephalitis lethargica.

(Wellcome Images, CC BY 4.0)

There does appear to be an auto-immune element to the disease with nearly all sufferers showing damage to the brain stem consistent with it coming under attack from the body's immune system. This, combined with the disease's first appearance around the same time as the flu pandemic, has led to speculation that it comes from the body's overreaction to a virus. But that's still not certain.

Analysis of other influenza and viral outbreaks, both before World War I and after, show some connection between viral outbreaks and the onset of encephelitis lethargica.

It's still possible that the world could see a sudden resurgence of encephelitis lethargica, especially if there's a new influenza outbreak, but our luck has held for over 70 years — fingers crossed.