What Parkinson's Tremor

Parkinson’s disease (PD) is a progressive and chronic neurodegenerative disorder which is characterised by tremors, slow movements , postural instability and rigidity. Tremors are one of the most common symptoms and it is thought that 75% of people with PD will be affected by tremors at some point in their disease progression. There are several forms of tremors which can develop, with those at rest being the most common.¹

This article aims  to provide an overview of Parkinson’s tremors, including the symptoms, causes, affected  body parts and potential treatments.

Overview

​​PD is a progressive neurodegenerative disorder which affects people mainly later in life. It is the second most prevalent neurodegenerative disease globally, with the number of cases rising due to an increase in lifespan. Approximately 0.3% of the total world population is affected by PD, with this percentage increasing to 1% in people over the age of 60. PD can be characterised by distinct changes in the brain, with an area of the  brain called the substantia nigra, particularly affected.² Consequently, the release of a chemical messenger called dopamine is altered, which is thought to account for much of PD’s pathology.³ It is believed that up to 80% of dopamine-producing  cells in the substantia nigra are lost before the classical PD motor symptoms (tremors) emerge, with this often being the point in disease progression when PD is diagnosed.²

Parkinson’s tremors are one of the most common symptoms affecting people with PD and most sufferers at some point will experience them in their disease progression. It is perhaps the most challenging motor symptom of PD and therefore there has been extensive research into the origin of tremors and how they can potentially be treated. PD is a diverse disease which has several sub-types, which are classified by their predominant symptom. Patients with the tremor-dominant subtype typically have a slower-disease progression and less severe non-motor symptoms. Additionally, the severity and progression of tremors are thought to depend on several factors. Despite there being extensive research on tremors in PD, the exact disordered physiological processes underlying tremors remain unknown.¹

Symptoms of parkinson’s tremor

In general, tremors can be defined as a rhythmic and involuntary movement of a body part.⁴ There are two types of tremors which can be caused by PD:⁵

• Resting tremors - theseoccur when the body is not moving, for example, when lying in bed. The most common form of PD tremor is called a ‘pill-rolling’ tremor- this is due to the appearance that an individual is trying to roll a pill between their thumb and index finger
• Action tremor- this occurs when an individual with PD has a tremor whilst performing a task, such as drinking from a cup

Causes of parkinson’s tremor

Despite low dopamine levels  being a characteristic  of PD, tremors are not directly associated with dopamine depletion in the substantia nigra. Furthermore, the outcome of dopamine supplementation to treat tremors is varied. Some studies have shown that dopamine depletion in brain areas other than the substantia nigra may lead to PD tremors, such as another part of the midbrain called the retrorubral area.³ Evidence suggests that brain cells producing dopamine in the retrorubral area degenerate in people with tremor-dominant PD, leading to a decreasein levels of dopamine in other parts of the brain.¹ This is now generally thought to be one of the biological causes of tremors in PD.

Recent research has revealed that decreased dopamine levels may not be the only cause of PD tremors. One chemical messenger  which is thought to be involved is serotonin. Research suggests that a protein involved in the transportation of serotonin around the brain is depleted in people with PD. Additionally, the severity of tremors is associated with the amount of depletion of this protein.³

Furthermore, evidence has shown that another neurotransmitter system called the noradrenergic system may be the i of the causetremors, with it thought to be overactive in tremor-dominant PD patients. Studies have shown that cognitive stress and adrenaline injection, which both activate the nor adrenergic system, can lead to an increase in PD tremors. This has sparked interest in the medical community about whether drugs which target the nor adrenergic system may be effective for the treatment of PD tremors.³

Which body parts do parkinson’s tremors affect?

Parkinson’s tremors typically occur in the hands, with ‘pill-rolling’ tremors presenting the most common form of tremor. Additionally, tremors may present in other body parts such as the legs, lower lip, and jaw. There are also reports of some people experiencing internal tremors, such as a shaking sensation inside the chest, limbs, or abdomen. Therefore, tremors often affect sufferers of PD's daily lives.⁵

Tremors are generally the first motor symptoms that present in PD, with the majority of tremors occurring at rest. Typically, tremors, during the early stages of the disease, affect  one side of the body As the disease progresses, both sides of the body may be affected by tremors.⁵

Can parkinson's tremors go away?

There is currently no cure for PD tremors, but there are ways to manage them. These generally include:¹

• Medication- Levodopa and other dopaminergic agents
• Deep brain stimulation (DBS)
• Physical therapy and rehabilitation

How are parkinson’s tremors treated?

The most common treatment option for PD tremors is Levodopa and other dopaminergic agents. The choice of medication used often depends on individual factors such as tremor severity and sensitivity to levodopa. Levodopa is a drug that can be converted into dopamine in the brain, and therefore can help normalise the characteristic dopamine depletion seen in PD patients.¹ Even though levodopa is the typical treatment option for PD, how it is in treating tremors is variable and therefore other treatment options may need to be considered.

Deep brain stimulation (DBS) has emerged as the most common surgical intervention for the treatment of PD tremors. It has demonstrated long-term results in improving tremors, however, to qualify for DBS patients must undergo a detailed evaluation which includes cognitive status and responsiveness to levodopa treatment. It is still not clear how DBS can lead to improvement in tremor severity, but it is thought that it disrupts the abnormal interactions between neural circuits, which underlie the cause of tremors.¹

Finally, it has been shown that physical therapy and rehabilitation may be able to improve both the motor and non-motor aspects of PD. Specifically, resistance exercises show a beneficial effect in the improvement of tremors. Additionally, hand movement and cycling exercises have been demonstrated to be favourable at reducing tremor amplitude and frequency.¹

When to seek medical attention?

It is important to see your GP or a specialist if you start experiencing symptoms of Parkinson’s tremors. A specialist will then carry out a clinical assessment to analyse whether your symptoms are Parkinson’s tremors or if they have a different origin. Typically, further tests such as brain scans will also be conducted.⁵

Summary

PD is a chronic progressive neurodegenerative disorder, with around 75% of PD patients experiencing tremors. Tremors can be defined as involuntary and rhythmic movements of body parts. They typically affect the hands, legs, lower lip, and jaw, with the ‘pill-rolling’ tremor being the most frequent. There are different forms of tremors, but tremors at rest are the most common. Patients with tremor-dominant PD typically have slower disease progression and less severe non-motor symptoms. The exact biological cause of PD tremors is not known, but they are thought to arise due to disrupted neurotransmitter systems which can lead to abnormal interactions between neural circuits. There is currently no single cure for PD tremors, but they can be managed through medications such as levodopa, deep brain stimulation and physical therapy/rehabilitation.