Tremors are rhythmic, involuntary muscular contractions characterized by oscillations (to-and-fro movements) of a part of the body. The most common of all involuntary movements, a tremor can affect various body parts such as the hands, head, facial structures, vocal cords, trunk and legs; most tremors, however, occur in the hands. Tremors often accompany neurological disorders associated with aging. Although the disorder is not life-threatening, it can be responsible for functional disability and social embarrassment. There are many types of tremor and several ways in which tremors are classified. The most common classifications are by behavioral context and position. There are five such categories of tremor:

1. Resting. Resting or static tremor occurs when the muscle is at rest, for example when the hands are lying on the lap. This tremor usually stops during deliberate movement and is often seen in patients with Parkinson's disease. While commonly referred to as 'pill rolling' tremor of the hands, it can also affect the head, trunk, jaw and lips. It is often associated with other symptoms such as generalized slowness of motor activity, rigidity and postural instability.
2. Postural. Postural tremor occurs when a patient attempts to maintain posture, such as holding the hands outstretched. Postural tremors include physiological tremor, essential tremor, tremor with basal ganglia disease (also seen in patients with Parkinson's disease), cerebellar postural tremor, tremor with peripheral neuropathy, post-traumatic tremor, and alcoholic tremor.
3. Kinetic. Kinetic or intention (action) tremor occurs during purposeful movement, for example during finger-to-nose testing.
4. Task-specific. Task-specific tremor appears when performing goal-oriented tasks such as handwriting, speaking, or standing. This group consists primarily of writing tremor, vocal tremor, and orthostatic tremor.
5. Hysterical. Hysterical tremor, or psychogenic tremor, occurs in both older and younger patients. The key feature of this tremor is that it dramatically lessens or disappears when the patient is distracted.

Drugs can also cause tremor. The list includes caffeine, fluoxetine (Prozac), haloperidol (Haldol), lithium, methylphenidate (Ritalin), metoclopramide (Reglan), phenylpropanolamine, pseudoephedrine, theophylline and valproic acid.

Essential tremor (ET) is the most common movement disorder. It is a syndrome characterized by a slowly progressive postural and/or kinetic tremor, usually affecting both upper extremities. Tremor amplitude slowly increases over time. Tremor frequency decreases with increasing age. An 8 to 12 cycle per second tremor is seen in young adults and a 6 to 8 cycle per second tremor is seen in the elderly. Essential tremor can develop with aging and has no known cause.

Alcohol intake temporarily reduces tremor amplitude in approximately 50-70% of cases and 50 to 60% have a family history of ET. If shaking or trembling has been present for two or more years and you do not have an endocrine or hormonal imbalance, you may have essential tremor or Parkinson disease.

Conventional medications used for ET include primidone and propranolol. These medications provide good benefit in reducing tremor amplitude in 75% of patients.

If shaking or trembling has been present for less than 2 years, it may be caused by temporary conditions such as:

• Increased anxiety or stress
• Certain medications
• Caffeine excess or caffeine withdrawal
• Nicotine or smoking excess nicotine withdrawal
• Alcohol excess or alcohol/drug withdrawal

Effective treatment of tremor requires distinguishing this type of movement disorder from other movement disorders. Without being seen and examined by a physician, the cause of your tremor may be difficult to determine.