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What is Encephalitis Lethargica & How is it Treated?|Causes, Symptoms, Prognosis of Encephalitis Lethargica

What is Encephalitis Lethargica?

Appeared first in 1917 in the form of a wide spread epidemic, encephalitis lethargica is an unusual form of encephalitis. Also called “sleepy sickness” or “Nellysa disease”, this illness was discovered by a neurologist named Constantin von Economo. It is probably caused by a neurotropic virus and affects all age groups and both the sexes.

Encephalitis lethargica mainly affects babies, young children and seniors. Swamp dwelling birds and mosquitoes transmit this disease to humans and equine animals as well. Encephalitis lethargica is a seasonal disease and occurs mainly during summer and early autumn.

Encephalitis Lethargica can be acute, subacute or chronic in nature. The characteristic features of this disease are degenerative an inflammatory changes in the thalamus and around the mid-brain. Next are changes observed in the pons, medulla, and basal ganglia. Spinal cord can also get diffusely affected. The brain damage in encephalitis lethargica can at times leave patients in a statue-like state. The course of encephalitis lethargica varies significantly for different individuals, especially when accompanied by simultaneous or pre-existing disorders and diseases.

What Causes Encephalitis Lethargica?

The exact causes of encephalitis lethargica are not known yet. However, it is believed to be caused as a result of an auto-immune response which can be linked to pathologies or infectious viral, fungal, bacterial, rickettsia or parasitic diseases.

What are the Symptoms of Encephalitis Lethargica?

The symptoms of encephalitis lethargica are based on the stages and severity of the disease. In acute stage of encephalitis lethargica, there is extensive and persistent back and neck pain, headaches, delirium, and convulsions. The symptoms of encephalitis lethargica also include disturbances in sleep pattern, restlessness at night and insomnia. Visual disturbances like irregular eye movement, unequal pupils, blurred vision and doubled vision are also common symptoms in this illness. Patients also suffer from involuntary movements like myoclonus intention tremors.

The disease is progressive in nature and is known to cause potential brain damage like Parkinson’s disease. After being in its acute stage for some time, encephalitis lethargica disease either gets arrested or gradually passes into a chronic stage. Chronic form of encephalitis lethargica is marked by features of mental symptoms, parkinsonian syndrome, ocular abnormalities, somnolence, lethargy, fever, sore throat, tics, muscular pain, tremors, torticollis, oculogyric crisis, chorea and even coma. Parkinson-ism can develop over a period of months or years.

How is Encephalitis Lethargica Diagnosed?

Correct identification of the kind of encephalitis that the patient is suffering from is extremely important for deciding the appropriate course of treatment. The diagnosis of encephalitis lethargica is primarily based on the symptoms experienced by the patient. The doctor would also inquire about any recent illness or exposure to virus to get a proper history, which helps in diagnosis of encephalitis lethargica.

Certain tests may help to confirm the diagnosis of encephalitis lethargica, which include lumbar puncture, MRI scan or electroencephalogram (EEG). Blood tests to check the white blood cell count and presence of viruses or bacteria in the body may need to be conducted as well. The doctor can zero down on encephalitis lethargic if the patient’s condition cannot be linked to any other known neurological condition and they show influenza-like symptoms, hypersomnia, opthalmoplegia, awareness or being alert and psychiatric changes. Biopsy or analysis of brain tissue sample may be required to confirm the diagnosis of encephalitis lethargica.

How is Encephalitis Lethargica Treated?

Treatment of encephalitis lethargica includes modern approaches like immunomodulation therapies, and treatments to relieve specific symptoms. The treatment of encephalitis lethargica in the early stages primarily focuses on stabilizing the patient. It is very difficult to treat this disease in its initial stages and little evidence of consistent effectiveness of the treatments has been recorded so far. However, the conditions of some patients who have been given steroids have shown improvement. Parkinsonism is treated with anti-Parkinson drugs like levodopa. However, many patients who take this drug experience improvement in symptoms, which are short lived. Other kinds of encephalitis may also accompany encephalitis lethargica.

What is the Prognosis for Encephalitis Lethargica?

Prognosis of encephalitis lethargica varies but complete recovery occurs in just 20% of cases. Mortality rate in case of encephalitis lethargic is around 2% to 12%. This rate is higher in case of young children and survivors are left with chronic disabilities like blindness, hemiplegia, mental retardation and speech disorders.

How can Encephalitis Lethargica be Prevented?

With the advancement of medical science, certain potential causes of encephalitis lethargica can now be prevented successfully. Prevention of encephalitis lethargica is also possible by prevention of some related infections. The eradication of smallpox and vaccination against measles, mumps, and rubella (MMR) has considerably decreased the occurrence of encephalitis lethargica, especially in children. Vaccines have been developed for people who travel to high-risk regions as well. Some other ways of preventing this illness is by keeping oneself protected against mosquitoes and avoiding people with active viral illness which can further cause encephalitis lethargica.


  1. Vilensky JA, Foley P, Gilman S. Children and Encephalitis Lethargica: A Historical Review. Pediatr Neurol. 2007;37(2):79-84. doi:10.1016/j.pediatrneurol.2007.04.013
  2. National Institute of Neurological Disorders and Stroke. Encephalitis Lethargica Information Page. Accessed fromhttps://www.ninds.nih.gov/Disorders/All-Disorders/Encephalitis-Lethargica-Information-Page
  3. McCall S, Vilensky JA, Gilman S, Taubenberger JK. The Relationship Between Encephalitis Lethargica and Influenza: A Critical Analysis. J Neurovirol. 2008;14(3):177-185. doi:10.1080/13550280801998762
  4. Rana AQ, Qureshi AR, Rana MA. Postencephalitic Parkinsonism: Current Perspectives. Neuropsychiatr Dis Treat. 2018;14:2057-2065. doi:10.2147/NDT.S173726

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Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 1, 2023

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