A tremor is an involuntary, rhythmic movement of an area of the body normally under voluntary control. According to the National Institute of Neurological Disorders and Stroke, more than 20 different forms of tremors caused by varying mechanisms occur, with the hands most frequently affected. Some types of tremors occur transiently, while others are chronic and progressive.
Essential tremor is the most common form of the disorder, reports the National Institute of Neurological Disorders and Stroke. Essential tremor is not part of degenerative neurological disease; it occurs in isolation. The tremor most commonly affects the hands, although the muscles of the head, voice, arms, legs, tongue and trunk may be involved. Essential tremor is an intention tremor, meaning symptoms are provoked or increased with purposeful movement. Thus, essential tremor of the hands interferes with many daily tasks including writing, eating, buttoning clothing and grasping objects. Stress, emotional upset and caffeine or other stimulants may cause worsening symptoms. This disorder most commonly presents in people older than age 40. It may be progressive in some people with the condition. Information provided by MayoClinic.com indicates that approximately 50 percent of people with essential tremor have an inherited form of the disorder known as familial tremor. Among those who do not have familial tremor, the cause of essential tremor remains unclear.
Parkinson’s disease is a chronic disorder characterized by progressive deterioration of muscle control due to loss of nerve cells in the substantia nigra area of the brain. Tremor is usually the first symptom of Parkinson’s disease. At the onset of Parkinson’s disease, tremor affects one side of the body. Most commonly, one of the hands is affected, although tremor may first appear in the jaw or foot. A Parkinson’s disease tremor is a resting tremor, meaning it is worst at rest and improves with intentional movement--the opposite of essential tremor. As Parkinson’s disease progresses, tremors occur on both sides of the body and become increasingly severe. Parkinson’s disease treatment can decrease symptom severity but does not alter the disease course.
Certain metabolic disturbances can cause tremors, which represent an exaggerated form of an imperceptibly low-level tremor that occurs in all people. A low blood sugar level, an overactive thyroid gland or alcohol withdrawal can provoke these tremors, known as enhanced physiologic tremors. Enhanced physiologic tremors may also occur as a side effect of certain medications including bronchodilators, lithium, theophylline, valproate, metoclopramide, amiodarone and certain antipsychotic drugs.