Encephalitis lethargica

Overview
Encephalitis lethargica (EL) is an atypical form of encephalitis. Also known as sleeping sickness (though different from the sleeping sickness transmitted by the tsetse fly), EL is a devastating illness that swept the world in the 1920s and then vanished as quickly as it had appeared. First described by the neurologist Constantin von Economo in 1916, EL attacks the brain, leaving some victims in a statue-like condition, speechless and motionless. 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 from disease-related causes.

Symptoms
Encephalitis lethargica 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.

Cause
The cause of encephalitis lethargica is not known for certain.

Research in 2004 suggested that the disease is due to an immune reaction. In this study, many of the people with encephalitis lethargica had experienced recent pharyngitis and the authors found some evidence linking the reaction to prior strep throat. They hypothesised that encephalitis lethargica, Sydenham's chorea and PANDAS (paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections) are mediated by variations of the post-streptococcal immune response.

There is also some evidence of an autoimmune origin with antibodies (IgG) from patients with EL binding to neurons in the basal ganglia and mid-brain.Western immunoblotting showed that 95% of EL patients had autoantibodies reactive against human basal ganglia antigens.By contrast, antibodies reactive against the basal ganglia were found in only 2-4% of child and adult controls (n = 173, P < 0.0001).

Some researchers believe that new data supports the influenza hypothesis, while others consider this less likely.

Treatment
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 some patients given steroids have seen improvement. 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 anti-parkinson 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.