Encephalitis lethargica (EL) is a serious sporadic form of encephalitis. Since the late 16th century, there have been reports from various European countries describing epidemic outbreaks of disease that seems at least to have been similar to EL. The name encephalitis lethargica itself was coined by the neurologist Constantin Von Economo at an early stage of the epidemic that occurred during and after the First World War. Difficulty of diagnosis and the lack of statistical records in many countries mean that estimates of the number of cases have varied greatly.
However, modern reports suggest that perhaps half a million or more people were affected, of whom about one-third died. Patients who survived EL often develped a form of parkinsonism called post-encephalitis Parkinson's disease, which results in serious neurological disability. An understanding of the mechanism of post-encephalitis parkinsonism may also shed light on the causes of Parkinson's disease.
Although the last epidemic of EL occurred over three quarters of a century ago, the cause was never scientifically established, and remains a matter of controversy today. This makes diagnosis difficult, and is one of the reasons why we do not know how many cases of EL there have been in recent times.
Better awareness, knowledge and understanding of EL could significantly improve diagnosis and treatment. Research into EL is therefore essential.
The "Spanish" influenza epidemic of 1918 and EL
Literature survey and diagnostic criteria
Symptoms of EL