Just after World War I, a viral disease called encephalitis lethargica attacked almost 5 million people throughout the world and then suddenly disappeared in the 1920s. Known as sleeping sickness in the United States, this disease killed one-third of its victims and led to post-encephalitic parkinsonism in many others.
Post-encephalitic parkinsonism is a particularly severe form of movement disorder in which some people develop disabling neurological disorders, including various forms of catatonia, often years after the acute phase of the illness has passed. (In 1973, neurologist Oliver Sacks published Awakenings, an account of his work in the late 1960s with post-encephalitic patients in a New York hospital. Using the then-experimental drug levodopa, Dr. Sacks was able to temporarily "awaken" these people from their statue-like state. A film by the same name was released in 1990.)
In rare cases, other viral infections, including western equine encephalomyelitis, eastern equine encephalomyelitis, and Japanese B encephalitis, can leave people with Parkinson's disease-like symptoms.
A reversible form of parkinsonism sometimes results from the use of certain drugs, such as chlorpromazine and haloperidol, prescribed for people with psychiatric disorders.
Some drugs used for stomach disorders (metoclopramide) and high blood pressure (reserpine) may also produce parkinsonian symptoms. However, stopping the medication or lowering the dosage often causes the symptoms to go away or become less severe.
In this form of parkinsonism, the substantia nigra is only mildly affected, while other brain areas show more severe damage than that which occurs in people with primary Parkinson's disease. People with this type of parkinsonism tend to show more rigidity, and the disease progresses more rapidly.