Dr Trisha Macnair
This mysterious illness, also known as sleeping sickness, can cause fever, headache, weakness and other symptoms, which can lead to a prolonged state of unconsciousness or to Parkinson's disease.
The cause remains a mystery.
Between 1917 and 1928 a puzzling illness swept around the world. Young people, especially women, seemed to be most vulnerable, although it affected people of all ages.
Doctors named it encephalitis lethargica, which simply means 'inflammation of the brain that makes you tired'.
Thousands of people were struck down and many survivors were left to battle difficult symptoms for years afterwards.
Some thought it was caused by a virus, some confused it with the Spanish flu epidemic of the time, while others blamed weapons used in World War I. But scientists are still not clear what causes the condition.
Although an epidemic of encephalitis lethargica hasn't recurred, occasional cases had been reported beforehand and are still sometimes seen. Some experts suggest it may be more common than we realise, but that many more minor cases go undiagnosed.
Doctors in south-west England are trying to pin down exactly how common it is. You can see details at www.thesophiecamerontrust.org.uk.
Many other names have been given to the condition or to diseases that appear to cause the same symptoms. These include Von Economo's disease, Cruchet's disease, Akureyri disease (after a similar epidemic in Iceland in 1948), benign myalgic encephalomyelitis and sleeping disease.
The illness usually starts with a high fever, headache and sore throat
The symptoms of encephalitis lethargica can be variable, but the illness usually starts with a high fever, headache and sore throat.
Double vision, disturbance of eye movements, weakness of the upper body, tremors and strange movements, neck stiffness, intense muscle pains, a slowing of physical and mental response, drowsiness and lethargy soon follow.
Unusual brain and nerve symptoms may occur, and the person's behaviour and personality may change too. Occasionally, they become psychotic with extremely disturbed thinking.
Sometimes the illness is mistaken for epilepsy, hysteria or even drug or alcohol abuse.
This is why the disease is sometimes known as sleeping sickness.
Many died during the 1920s' epidemic, but modern medicine can help to keep people alive.
The disease leaves a variety of problems that can cause prolonged disability
However, the disease leaves a variety of problems that can cause prolonged disability. Most people recovering from encephalitis lethargica develop a form of Parkinson's disease, with typical symptoms of
slowness, tremor and abnormal muscle movements called dystonia. As with Parkinson's there may be little facial movement, so although the person can hear, understand and is mentally fine, they don't appear to respond much to the world around them.
These problems may develop as long as a year after recovery. There may also be problems with swallowing or vision, as well as long-term behavioural disorders. However, some people do manage to make a full recovery.
Many people believe a virus or other type of infection may be to blame for encephalitis lethargica, but there's not yet good evidence of any particular organism.
Some researchers have suggested it might be an auto-immune disease, where the body's immune system is triggered by a throat infection (perhaps with a streptococcus bacteria) to attack the nervous system.
Research shows that areas of the brain called the mid-brain and basal ganglia become inflamed during the illness. But while anti-brain antibodies can be detected, no viruses have been found. This suggests the syndrome isn't caused by a virus directly entering and attacking the brain, so could it be that the body's own immune cells are attacking the nerve cells here?
As long as the cause of encephalitis lethargica remains unknown, it's difficult to give specific treatment or prevent the disease. There's no cure for the condition. Instead, treatment is targeted at supporting the person through their illness and dealing with the symptoms as they occur.
In the early stages, treatment in an intensive care unit may be necessary to keep the person breathing, fed and protected from other infections, especially if they're in a coma. Steroid drugs may help to reduce inflammation in the brain.
As the person recovers, physiotherapy, nutritional support and speech therapy may all help to speed them on the path back to normality. They may also need psychological support to deal with emotional and behavioural problems.
The Sophie Cameron Trust
Kelston House, College Road, Lansdown, Bath BA1 5RY
Tel: 01225 424224
This article was last medically reviewed by Dr Rob Hicks in December 2005.