Tremor is categorized based on when and how the tremor is activated. These categories are rest and action tremor. Rest tremor occurs when people are at rest. People with Parkinson’s disease often experience rest tremor. Action tremor occurs when a muscle is moved voluntarily. There are several sub-classifications of action tremor, many of which overlap.
- Postural tremor occurs when holding a position against gravity, such as holding the arms outstretched.
- Kinetic tremor is associated with any voluntary movement, such as moving the wrists up and down or closing and opening your eyes.
- Intention tremor starts when the person makes an intended movement toward a target, such as lifting a finger to touch their nose.
- Task-specific tremor only appears when performing goal-oriented tasks such as handwriting or speaking.
- Isometric tremor occurs during a voluntary muscle contraction that is not accompanied by any movement, such as when holding a heavy book in the same position.
Tremor syndromes are defined based on the pattern of the tremor. Some of the most common forms include:
Essential tremor
Essential tremor (previously also called benign essential tremor or familial tremor) is one of the most common movement disorders. Its key feature is a tremor in both hands and arms during action without other neurological signs. It also may affect a person’s head, voice, or lower limbs. Although the tremor can start at any age, it most often first appears during adolescence or in middle age (between ages 40 and 50). It can be mild and stay mild, or slowly get worse over time.
The exact cause of essential tremor is unknown. Studies show essential tremor is accompanied by a mild degeneration of the cerebellum, which is the part of your brain that controls movement coordination. Essential tremor is an inherited condition in 50-70% of cases (referred to as familial tremor). Familial forms often appear early in life.
Dystonic tremor
Dystonic tremor occurs in people who are affected by dystonia—a movement disorder in which incorrect messages from the brain cause muscles to be overactive, resulting in abnormal postures or sustained, unwanted movements. The disorder usually appears in young or middle-aged adults and can affect any muscle in the body, but most commonly affects the neck (cervical dystonia), vocal cords (laryngeal dystonia), or arms/legs (limb dystonia). A person with dystonic tremor can sometimes relieve their tremor by relaxing completely or touching the affected body part or muscle.
Cerebellar tremor
Cerebellar tremor is typically a slow, big (high amplitude) tremor of the arms, legs, hands, or feet that worsens at the end of a purposeful movement such as pressing a button. It is caused by damage to the cerebellum and its pathways to other brain areas, often from a stroke or tumor, injury from a disease or an inherited disorder, or from chronic damage due to alcohol use disorder.
Functional tremor
Functional tremor (also called psychogenic tremor) can appear as any form of tremor. Its symptoms may vary but often start suddenly and fluctuate widely. The tremor may increase with attention and decrease or disappear when the person is distracted.
Enhanced physiologic tremor
Enhanced physiologic tremor typically involves a fine amplitude (small) action tremor in both the hands and the fingers. It is generally not caused by a neurological disease but by reaction to certain drugs, alcohol withdrawal, or medical conditions including an overactive thyroid and hypoglycemia. It is potentially reversible once the cause is corrected.
Parkinsonian tremor
Parkinsonian tremor is common and one of the first signs of Parkinson's disease, although not all people with Parkinson's disease have tremor. Its shaking is most noticeable when the hands are at rest and may look as if someone's trying to roll a pill between the thumb and a finger. Parkinson's tremor may also affect the chin, lips, face, and legs. The tremor may initially appear in only one limb or on just one side of the body but may spread to both sides as the disease progresses. The tremor is often made worse by stress or strong emotions.
Orthostatic tremor
Orthostatic tremor is a rare disorder characterized by rapid muscle contractions in the legs that occur when a person stands up. The tremor usually stops when the person sits down or walks. Standing may make the person feel unsteady or unbalanced, causing them to try to sit or walk. Because this type of tremor involves very fast shaking, it may not be visible to the naked eye. Orthostatic tremor can be felt by touching the person’s thighs or calves or when a doctor listens to the muscle activities with a stethoscope. In some cases, the tremor can become more severe over time. The cause of orthostatic tremor is unknown.