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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Encephalitis lethargica | 1/2 | https://en.wikipedia.org/wiki/Encephalitis_lethargica | reference | science, encyclopedia | 2026-05-05T11:04:25.215156+00:00 | kb-cron |
Encephalitis lethargica (EL) is an atypical form of encephalitis. Also known as "von Economo Encephalitis", "sleeping sickness" or "sleepy sickness" (distinct from tsetse fly–transmitted sleeping sickness), it was first described in 1917 by neurologist Constantin von Economo and pathologist Jean-René Cruchet. The disease attacks the brain, leaving some victims in a statue-like condition, speechless and motionless. Between 1915 and 1926, an epidemic of encephalitis lethargica spread around the world. The exact number of people infected is unknown, but it is estimated that more than one million people contracted the disease during the epidemic, which directly caused more than 500,000 deaths. Most of those who survived never recovered their pre-morbid vigor.
== Signs and symptoms == Encephalitis lethargica is characterized by high fever, sore throat, headache, lethargy, double vision, delayed physical and mental response, sleep inversion and catatonia. In severe cases, patients may enter a coma-like state (akinetic mutism). Patients may also experience abnormal eye movements ("oculogyric crises"), Parkinsonism, upper body weakness, muscular pains, tremors, neck rigidity, and behavioral changes including psychosis. Klazomania, a vocal tic involving compulsive screaming, is sometimes present. Approximately a third of the affected children experienced change of behavior, with many of them becoming "delinquents". Boys between the ages of 5 and 18 years were the most affected. Symptoms include change of personality, restlessness, irregular sleeping habits, emotional instability manifesting as irritability, crying spells, and temper tantrums, including impulsivity, and unpredictability, what Economo described as "moral insanity". More extreme cases include aggression and "shameless sexual activity". Children under the age of 5 years suffered severe developmental delays. Delays were also present in children between 5 and 14 years of age, even though the claims are controversial. It is estimated that 25–90% of adults also suffered from psychological problems, including hysteria and abnormal behavior and movement. A large minority of patients described having bradyphrenia.
== Cause ==
The causes of encephalitis lethargica are uncertain. Though it used to be believed that it was connected to the Spanish flu epidemic, modern research provides arguments against this claim. Some studies have explored its origins in an autoimmune response, and, separately or with an immune response, links to pathologies of infectious disease – viral and bacterial, such as in the case of influenza, where a link with encephalitis is clear. Postencephalitic Parkinsonism was clearly documented to have followed an outbreak of encephalitis lethargica following the 1918 influenza pandemic; evidence for viral causation of the Parkinson's symptoms is circumstantial (epidemiologic, and finding influenza antigens in encephalitis lethargica patients), while evidence arguing against this cause is of the negative sort (for example, lack of viral RNA in postencephalitic Parkinsonian brain material). In reviewing the relationship between influenza and encephalitis lethargica (EL), McCall and co-authors conclude, as of 2008, that "the case against influenza [is] less decisive than currently perceived ... [yet] there is little direct evidence supporting influenza in the etiology of EL," and that "[a]lmost 100 years after the EL epidemic, its etiology remains enigmatic." Hence, while opinions on the relationship of encephalitis lethargica to influenza remain divided, the preponderance of literature appears skeptical. The German neurologist Felix Stern, who examined hundreds of encephalitis lethargica patients during the 1920s, noted that their encephalitis lethargica typically evolved over time:
The early symptoms would be dominated by sleepiness or wakefulness. A second symptom would lead to an oculogyric crisis. The third symptom would be recovery, followed by a Parkinson-like syndrome. If patients of Stern followed this course of disease, he diagnosed them with encephalitis lethargica. Stern suspected encephalitis lethargica to be close to poliomyelitis, but had no evidence. Nevertheless, he experimented with the convalescent serum of survivors of the first acute syndrome. He vaccinated patients with early-stage symptoms, telling them that it might be successful. Stern is the author of the definitive book, Die Epidemische Encephalitis. In 2010, in a substantial compendium reviewing the historic and contemporary views on EL, it quotes a researcher, writing in 1930, who stated, "we must confess that etiology is still obscure, the causative agent still unknown, the pathological riddle still unsolved", and went on to offer the following conclusion, as of that publication date:
Does the present volume solve the "riddle" of EL, which ... has been referred to as the greatest medical mystery of the 20th century? Unfortunately, no: but inroads are certainly made here pertaining to diagnosis, pathology, and even treatment.
After the publication of this compendium, an enterovirus was discovered in encephalitis lethargica cases from the epidemic. In 2012, Oliver Sacks, the author of the book Awakenings, about institutionalized survivors, acknowledged this virus as the probable cause of the disease. Other sources have suggested Streptococcus pneumoniae as a cause.
== Diagnosis == There have been several proposed diagnostic criteria for encephalitis lethargica. One, which has been widely accepted, includes an acute or subacute encephalitic illness where all other known causes of encephalitis have been excluded. Another diagnostic criterion, suggested more recently, says that the diagnosis of encephalitis lethargica "may be considered if the patient's condition cannot be attributed to any other known neurological condition and that they show the following signs: influenza-like signs; hypersomnolence (hypersomnia), wakeability, ophthalmoplegia (paralysis of the muscles that control the movement of the eye), and psychiatric changes". Others describe lethargy, "mask-like faces", excess blood in the meninges, and other general neurological symptoms.
== Treatment ==
Modern treatment approaches to encephalitis lethargica include immunomodulating therapies and treatments to remediate specific symptoms. There is little evidence so far of a consistent effective treatment for the initial stages, though some patients given steroids have seen improvement. The disease becomes progressive, with evidence of brain damage similar to that of Parkinson's disease. Treatment is then symptomatic. L-DOPA (Levodopa) and other anti-Parkinson drugs often produce dramatic responses; however, most people given L-DOPA experience improvements that are short-lived.
== History ==
=== Occurrences === Retrospective diagnosis tentatively suggests various historical outbreaks of encephalitis lethargica: