Essential Tremor and Parkinson’s Disease

Parkinson’s disease (PD) and essential tremor are both primarily movement disorders. The symptoms are commonly confused with each other, mainly because essential tremor is not as well known as PD even though essential tremor is more prevalent. High-profile people like Michael J. Fox and Muhammad Ali raised our awareness of PD in the 1990s just like Pres. Ronald Reagan did with Alzheimer’s disease in the 1980s. Because of this, essential tremor is not as well-known to the general public even though more people suffer from it than from PD.

The two disorders differ in etiology and symptoms. Scientists understand the cause of PD quite well. It manifests when there is a loss of about 80% of the dopamine-producing neurons in the substantia nigra, a small area within the brainstem. However, we do not know what causes the death of these dopamine-producing cells. The etiology of essential tremor is not understood as well. What we do know is that the mechanics of essential tremor, like PD, involve the deep nuclei and white matter of the brain, including the thalamus and striatum.

The symptoms of PD include tremor, rigidity, akinesia, and postural instability. Bradykinesia (slowed movements) and bradyphrenia (slowed cognition) are also common symptoms. If tremor is present in PD (and it does not have to be), it is manifest mainly as a resting tremor. However, when someone with PD moves and tries to do something, the tremor usually goes away. In other words, there is less of an action tremor than a resting tremor. Emotional changes are also common; depression and facial masking (little facial expression of emotion) are particularly prevalent. With essential tremor it is more common to have just an action (or intention) tremor and a postural tremor. Both diseases are progressive (although some forms of essential tremor do not progress). Both diseases can be very debilitating. Additionally, patients with essential tremor are more likely to develop or have PD.

Treatment of PD usually starts with some form of levodopa, a precursor molecule the body can turn into dopamine. Treatment of essential tremor usually involves taking various pharmaceuticals, including beta-blockers or anti-seizure medications. Deep brain stimulation (DBS) of the subthalamic nucleus, globus pallidus, or thalamus are becoming more common treatments of both essential tremor and PD (and pleasure). DBS was approved for treatment of essential tremor in 1997 and for PD in 2002. While we still have a lot to learn about these two diseases, we have come a long way in understanding and treating them.