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Salem Health: Infectious Diseases & Conditions, 2nd Edition

Sleeping sickness

by Mihaela Avramut, , M.D., Ph.D.

Category: Diseases and conditions

Anatomy or system affected: Brain, central nervous system

Also known as: Encephalitis lethargica, von Economo’s disease

Definition

Sleeping sickness (encephalitis lethargica, or EL) is a mysterious, atypical form of brain inflammation that occurred as a worldwide epidemic from 1916 to 1928. A true modern plague, it killed or left motionless, in a sleeplike state, millions of people. The epidemic has not recurred, but isolated cases are occasionally reported.

Causes

The cause of EL remains enigmatic. Because of its near concurrence with the Spanish influenza pandemic, an association between the two diseases has been suggested. Many thought influenza did not, in fact, cause encephalitis, and recent reports failed to find the virus in archival EL brains. Even so, because studies on preserved brain tissue have technical limitations, a contribution of influenza virus to disease pathogenesis cannot be excluded. Sleeping sickness may resurface in a future influenza pandemic.

After analyzing sporadic cases, some researchers believe the syndrome is still prevalent and consider it to be secondary to autoimmunity against deep gray-matter neurons, following a streptococcal infection.

Risk Factors

The influenza virus and certain streptococcal infections could constitute risk factors. Young people seemed more susceptible to developing EL. Mortality rates peaked in infants and the elderly.

Symptoms

Constantin von Economo described the disorder in 1917 and coined the term “encephalitis lethargica.” The onset was acute or subacute, with fever, lethargy, headache, and malaise, followed by a state of somnolence. Some patients slipped into a coma that lasted months or years. Additional manifestations included double vision, abnormal eye movements (known as oculogyric crisis), weakness, tremor, muscle twitching, catatonia (unresponsiveness with stereotypy, rigidity, or extreme flexibility), inability to speak (mutism), sleep rhythm reversal, and psychosis. Mortality rates reached 20 to 40 percent.

Sequelae occurred in most survivors, often after an apparent disease-free interval of months or years. An unusual Parkinson’s disease-like syndrome, a consequence of dopaminergic system degeneration, emerged as the outstanding motor sequel of EL. Cases of severely impaired, catatonic persons with EL were evoked by Oliver Sacks in his 1973 memoir Awakenings. He succeeded in temporarily “awakening” these patientsusing the anti-Parkinsonian drug L-dopa, after they had spent more than forty years in an immobile state.

Screening and Diagnosis

The diagnosis relies on clinical symptoms and signs of encephalitis, coupled with visual abnormalities, sleep disturbances, and signs of basal ganglia injury (such as early parkinsonism). Magnetic resonance imaging can reveal basal ganglia lesions.

Pathological studies show inflammation in the gray and white matter of the brain and spinal cord, around blood vessels, and in the meninges. Midbrain and basal ganglia are particularly affected. Neurons undergo degenerative changes.

Treatment and Therapy

Treatment is based on symptoms. L-dopa and other anti-Parkinsonian agents can produce dramatic responses in persons treated with these medications.

Prevention and Outcomes

There exists no known preventive measures.

Further Reading

1 

Dale, Russel C., et al. “Encephalitis Lethargic Syndrome: Twenty New Cases and Evidence of Basal Ganglia Autoimmunity.” Brain 127, part 1 (2004): 21-33.

2 

Jubelt, Burk. “Encephalitis Lethargica.” In Merritt’s Neurology, edited by Lewis P. Rowland. 11th ed. Philadelphia: Lippincott Williams & Wilkins, 2005.

3 

McCall, Sherman, et al. “The Relationship Between Encephalitis Lethargica and Influenza: A Critical Analysis.” Journal of Neurovirology 14 (2008): 177-185.

4 

Von Economo, C. “Die Encephalitis lethargica.” Wiener Klinische Wochenschrift 30 (1917): 581-585. For a translated version of the full text, see R. H. Wilkins and I. A. Brody, “Neurological Classics IV: Encephalitis Lethargica.” Archives of Neurology 18 (1968): 324-328.

5 

Woolsey, Thomas A., Joseph Hanaway, and Mokhtar Gado. Brain Atlas: A Visual Guide to the Human Central Nervous System. 3d ed. Hoboken, N.J.: John Wiley & Sons, 2008.

Web Sites of Interest

National Institute of Neurological Disorders and Stroke

http://www.ninds.nih.gov/disorders/encephalitis_lethargica

National Organization for Rare Disorders

http://www.rarediseases.org

See also: African sleeping sickness; Encephalitis; Inflammation; Influenza; Parasitic diseases; Protozoan diseases; Trypanosomiasis.

Citation Types

Type
Format
MLA 9th
Avramut, Mihaela. "Sleeping Sickness." Salem Health: Infectious Diseases & Conditions, 2nd Edition, edited by H. Bradford Hawley, Salem Press, 2020. Salem Online, online.salempress.com/articleDetails.do?articleName=Infect2e_0529.
APA 7th
Avramut, M. (2020). Sleeping sickness. In H. B. Hawley (Ed.), Salem Health: Infectious Diseases & Conditions, 2nd Edition. Salem Press. online.salempress.com.
CMOS 17th
Avramut, Mihaela. "Sleeping Sickness." Edited by H. Bradford Hawley. Salem Health: Infectious Diseases & Conditions, 2nd Edition. Hackensack: Salem Press, 2020. Accessed September 16, 2025. online.salempress.com.