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 patients 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." 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 Parkinsons 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:

In 1580, Europe was swept by a serious febrile and lethargic illness that led to Parkinsonism and other neurological sequelae. In 1673–1675, a similar serious epidemic occurred in London, which Thomas Sydenham described as "febris comatosa". In 1695, a 20-year-old woman in Germany experienced oculogyric crises, Parkinsonism, diplopia, strabismus, and other symptoms following an attack of somnolent brain fever, as described by Albrecht of Hildesheim. In 1712–1713, a severe epidemic of Schlafkrankheit (sleep sickness) occurred in Tübingen, Germany, followed in many cases by persistent slowness of movement and lack of initiative (aboulia).
Cinchonism is a pathological condition caused by an overdose of quinine or its natural source, cinchona bark. Quinine and its derivatives are used medically to treat malaria and lupus erythematosus. In much smaller amounts, quinine is an ingredient of tonic drinks, acting as a bittering agent. Cinchonism can occur from therapeutic doses of quinine, either from one or several large doses. Quinidine (a Class 1A anti-arrhythmic) can also cause cinchonism symptoms to develop with as little as a single dose. Signs and symptoms
Signs and symptoms of mild cinchonism (which may occur from standard therapeutic doses of quinine) include flushed and sweaty skin, ringing of the ears (tinnitus), blurred vision, impaired hearing, confusion, reversible high-frequency hearing loss, headache, abdominal pain, rashes, drug-induced lichenoid reaction (lichenoid photosensitivity), vertigo, dizziness, nausea, vomiting and diarrhea. Large doses of quinine may lead to severe (but reversible) symptoms of cinchonism: skin rashes, deafness, somnolence, diminished visual acuity or blindness, anaphylactic shock, and disturbances in heart rhythm or conduction, and death from cardiotoxicity (damage to the heart). Quinine may also trigger a rare form of hypersensitivity reaction in malaria patients, termed blackwater fever, that results in massive hemolysis, hemoglobinemia, hemoglobinuria, and kidney failure. Most symptoms of cinchonism (except in severe cases) are reversible and disappear once quinine is withdrawn.