Many medical conditions cause hand tremors, including neurological diseases such as multiple sclerosis and Parkinson's disease, according to the National Institute of Neurological Diseases and Stroke. Traumatic brain injury, stroke and alcoholism also cause hand tremors in some people, as does liver disease, mercury poisoning or an overactive thyroid. Medicines such as corticosteroids, amphetamines and those used to treat some psychiatric disorders cause tremors as well. Doctors classify tremors according to their appearance and their cause.
Essential tremors are the most common form of abnormal tremors, explains the NINDS. A result of mild degeneration of the cerebellum, the part of the brain that controls voluntary movement and gait, essential tremors usually appear in the hands, but other parts of the body are sometimes involved. This type of tremor is often inherited and is most common after the age of 40, although it can occur at any time. Stress, low blood sugar, fever or physical exhaustion often triggers essential tremors or makes them worse.
Parkinsonian tremors are often the first visible sign of Parkinson's disease, reports the NINDS. Usually occurring when the person is at rest, they appear as "pill-rolling" movements of the hand, usually beginning on one side of the body and eventually progressing to the other side. This type of tremor is greatly enhanced by emotion and stress.
Cerebellar tremors typically result from damage to the cerebellum by a tumor, stroke, multiple sclerosis or other neurodegenerative disease, the NINDS explains. Chronic alcoholism and overuse of some medications cause this type of tremors as well. They usually occur with active movement, such as reaching for something or touching a finger to the nose.