In medical terms, tremor is defined as an involuntary, rhythmic, and oscillatory movement of a body part. It is the most common movement disorder and can occur in any individual in the form of physiologic tremor. The physiological tremor is common and can occur in a healthy individual, and the symptoms of tremor are quite subtle and can hardly be seen through a naked eye. It is an involuntary shaking of the body, and there are many reasons for it.
There are several factors that can generate oscillation in the central nervous system and becomes the cause of tremor. It is difficult to know the exact cause of tremor but some of the factors that are interconnected to each other include, the ventromedial nucleus of the thalamus, the red cerebellar nucleus, and the bulbar olive, which constitutes the thalamus cerebellum olive circuit. The symptoms of tremor depend on the affected body part and the cause of the tremor. Most of the time, tremor affects hands and legs, but it can also affect the head, face, trunk, and vocal cords.
Classifications of tremors
Clinically, tremors are classified into two types - resting tremors and action tremors.
1. Resting tremor
It is the type of tremors that occur in a relaxed body when there is no movement, for example, when lying on a bed or sitting in a chair. This type of tremor occurs at a frequency band of 6 and 4 Hz, and it disappears when any voluntary movement is performed. Also, the aptitude of rest tremor often increases during mental stress.
2. Action tremor
It is the type of tremor that occurs whenever there is any voluntary contraction of a muscle. Action tremor is further sub-divided into various types:
- Postural tremor - The postural tremor occurs when an affected part of the body is kept in a position that is contrary to the action of gravity. For example, pointing at the object or sitting in a chair without any support for the upper body.
- Kinetic tremor - The kinetic tremor occurs during a voluntary movement such as writing, drawing, drinking, and eating. Kinetic tremor is divided into two types- simple kinetic tremor and intention kinetic tremor. Simple kinetic tremor increases with a movement on extremities, and intention kinetic tremor increases with target-directed movement.
- Physiologic tremor - The physiologic tremor is a postural tremor that is experienced by every individual. Enhancement of physiologic tremor is the most common cause of postural tremor.
- Task-specific tremor - Task-specific tremor is largely limited to specific tasks or movements such as writing. Kinetic tremor may worsen during certain activities such as primary writing tremor.
Syndromes linked to tremors
All types of tremors are not life-threatening, but it can be a sign of some serious underlying condition; therefore, it should be evaluated by the doctor to rule out an underlying condition. Some of the syndromes that are linked to tremor include:
1. Parkinson disease
Parkinson's disease is a degenerative disorder of the central nervous system that affects the person’s ability to perform common daily activities. It is characterized by tremors, bradykinesia, postural instability, and rigidity. In Parkinson’s disease, due to the loss of dopamine secretion, the neurons fire themselves collectively in a periodic manner, and this leads to the occurrence of resting tremor.
The severity of the symptoms vary from person to person; some patients may have a severe tremor, while others may have mild or no tremor at all. Generally, patients with Parkinson’s disease have a resting tremor of low frequency, which starts with hands and legs and is accompanied by rigidity and postural instability. Parkinson’s disease generally starts at around 50 years of age, and it is more common in males as compared to females.
2. Dystonic tremor
Dystonia is a term which refers to a disease of muscle contraction. It is an involuntary muscle contraction that results in postural abnormalities of the limbs, trunk, and face. Tremor is one of the common symptoms of dystonia, and there are many causes of it. Involuntary shaking of the head occurs when the neck muscles intermittently contract. Dystonic tremor is not consistent, and some sensory tricks such as light touch or placement of head on the headrest may lead to a decrease in the frequency of tremor. According to the researchers, tremor is more common in females as compared to males, and mostly it is associated with twisting of head and neck into abnormal positions.
3. Essential tremor
Essential tremor is the most common cause of neurological disorder that causes action tremor, and most often, it affects the hands and arms. It can affect other parts of the body as well such as head, chin, trunk, and voice and in essential tremor, tremor in the legs is quite unusual. Some patients having essential tremor may also experience enhanced physiological tremor due to anxiety. It is also characterized by the isolated tremor of the head that can occur in the absence of abnormal posturing.
4. Orthostatic tremor
Orthostatic tremor is a weight-bearing hyperkinetic disorder that affects the gait. Leg symptoms are common and highly reported by patients having an orthostatic tremor. The symptoms include shaky and jerky legs, imbalance, sense of leg weakness, and leg discomfort. Leg symptoms are the most common symptoms of orthostatic tremor, but it can also affect other parts of the body, and some patients also report arm, head, and jaw tremors.
Tremors are quite common and could be the symptom of any underlying disease. Share this post with your family and friends to create awareness among them. Stay Safe, Stay Healthy!!