Essential tremor is a neurological disorder that can cause various parts of the body, such as the head or hands, to shake uncontrollably. It's caused by electrical fluctuations in the brain transmitting abnormal signals to the muscles. A patient with essential tremor in his dominant hand may find it difficult or impossible to write with a pen or pencil. Some patients have tremor that disrupt the muscles involved in speaking as well.
As Columbia University professor of neurology and epidemiology Dr. Elan D. Louis explained in a 2010 New York Times article, injecting Botox into the affected muscles can play a limited role in alleviating such symptoms. The idea is that it will block nerve transmissions and relax the muscles. But Louis warned: The more muscles that are affected by essential tremor, the less effective the injections are. Additionally, some patients also report weakness in the muscles that receive injections [source: New York Times].
According to the Johns Hopkins Medicine website, Botox is generally recommended for patients with severe head tremors. While hand tremors also can be reduced with the treatment, the injections are more difficult to administer and it's harder to obtain a clear functional improvement from them.