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Encephalitis lethargica
ICD-10 A85.8
ICD-9 049.8
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Encephalitis lethargica is an atypical form of encephalitis.

Encephalitis Lethargica, also known as sleeping sickness (though different from the sleeping sickness transmitted by the tsetse fly), is a devastating illness that swept the world in the 1920s and then vanished as quickly as it had appeared. Encephalitis Lethargica attacks the brain, leaving some victims like living statues, speechless and motionless, as if they fall asleep and do not wake up.

Between 1917 and 1928, an epidemic of encephalitis lethargica spread throughout the world, but no recurrence of the epidemic has since been reported, though isolated cases continue to occur. During the outbreak, over 5 million died, and some were left frozen inside their useless bodies, in institutions.


Encephalitis lethergica is characterized by high fever, sore throat, headache, double vision, delayed physical and mental response, sleep inversion, catatonia and lethargy. In acute cases, patients may enter a coma-like state (akinetic mutism). Patients may also experience abnormal eye movements, parkinsonism, upper body weakness, muscular pains, tremors, neck rigidity, and behavioral changes including psychosis.

Postencephalitic Parkinson's disease may develop after a bout of encephalitis, sometimes as long as a year after the start of the illness.


The cause of encephalitis lethargica is not yet known for certain, but on the basis of research by British doctors Russell Dale and Andrew Church, the disease is now thought to be due to a massive immune reaction to an infection by the streptococcus-like bacterium, diplococcus. There is also some evidence of an autoimmune origin with antibodies (IgG) from patients with EL binding to neurones in the basal ganglia and mid-brain. It had been hypothesised that encephalitis lethargica, Sydenham's chorea and PANDAS (paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections) are mediated by the same post-streptococcal immune response...

A BBC Horizon television programme on the potential for a world-wide outbreak of H5N1 Bird Flu broadcast on November 7, 2006 postulated that the 1920s outbreak of encephalitis lethargica might have been as a direct, delayed pathological result of the Spanish Flu pandemic.


Treatment for encephalitis lethargica in the early stages is patient stabilization, which may be very difficult. There is little evidence so far of a consistent effective treatment for the initial stages, though one patient who was given steroids initially has so far made a good recovery. Other patients have been less fortunate, and the disease then becomes progressive, with evidence of brain damage similar to Parkinson's disease. Treatment is then symptomatic. Levodopa (L-Dopa) and other antiparkinson drugs often produce dramatic responses. However in most of the patients who were given L-Dopa in the 1960s, the amelioration of the disease was short lived.

The course of encephalitis lethargica varies depending upon complications or accompanying disorders.


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