A tremor in one or both hands, arms, or legs is perhaps the most well known symptom of Parkinson’s disease (PD), although not all people with PD experience tremor. The tremor from PD is most obvious when the limb is at rest and not being used for purposeful movement, and is therefore called “resting tremor.” Tremor is one of the four primary motor symptoms that are characteristic of PD. The other three primary motor symptoms are rigidity (an abnormal stiffness in a limb or part of the body), postural instability (impaired balance or difficulty standing or walking), and bradykinesia (gradual loss and slowing down of spontaneous movement).1,2
Tremor as a symptom of early stage Parkinson’s disease
Approximately 70% of people experience a slight tremor in one of their hands or feet in the early stages of PD. The tremor can even begin as a rhythmic movement between the thumb and forefinger, called a “pill-rolling” movement. Occasionally, the tremor may appear first in the chin, lips, or jaw. The tremor appears as a shaking movement when the muscles are relaxed and not being focused on taking action. The tremor may worsened during times of high physical or emotional stress. Sleep, relaxation, or purposeful movement can alleviate the tremor. As PD progresses, the tremor may spread from just one area affected to both sides of the body affected. For example, the tremor may start in just the right hand and over time spread to both hands.1
Why does Parkinson’s disease cause tremor?
In PD, the neurons (nerve cells) in the brain are damaged and die. While PD affects multiple areas of the brain, one of the most heavily damaged is the substantia nigra pars compacta. The neurons in the substantia nigra produce dopamine, a neurotransmitter (chemical messenger) that relays the message from the substantia nigra to other parts of the brain to produce smooth, purposeful movement. These other parts of the brain are organized into a circuit called the basal ganglia. When PD damages large numbers of these dopamine-producing neurons, communications across neurons in this circuit are disrupted and the motor symptoms of PD appear, including tremor. Research has demonstrated that when the motor symptoms of PD appear, 60-80% of the neurons that generate dopamine have been destroyed.3
Treating tremor in Parkinson’s disease
There is no known cure for PD at this time, and there are not currently any treatments to slow or stop the natural progression of the disease. However, there are several treatments that can manage symptoms like tremor. Treatment is tailored to the individual and may include medications, surgery (deep brain stimulation), and complementary or alternative medicine.
Most people with PD are started on medication to help manage their symptoms. Initial therapy is usually levodopa (administered with carbidopa), dopamine agonists, and/or monoamine oxidase-B (MAO-B) inhibitors. The combination of levodopa and carbidopa is the most effective treatment available for the management of motor symptoms of PD. However, it can cause a side effect known as dyskinesia, which are abnormal involuntary movements. Dopamine agonists are less effective on the motor symptoms of PD but have a lower rate of causing dyskinesia, although they have other side effects. MAO-B inhibitors are less effective than levodopa or dopamine agonists, however they have fewer side effects. Choice of therapy should be customized to the individual person with an understanding of the risks and benefits of each class of medication.4
For some people with PD whose symptoms are not adequately controlled with medication, surgery to perform deep brain stimulation may be an option. As with medication, surgery does not cure or change the course of the disease progression, but it may help with the symptoms of PD.2