Distinguishing between essential tremor (ET) and Parkinson’s disease (PD) is key to developing a targeted and effective treatment plan.

Dr. Elena Bortan, a movement disorders specialist with the Chase Family Movement Disorders Center, part of the Hartford HealthCare Ayer Neuroscience Institute, said people often confuse the two conditions because tremor is a primary symptom of both.

“There are many differences between the signs and symptoms of the two disorders and it is critical that patients receive an accurate diagnosis early in the disease process to receive the appropriate treatment, education and support,” Dr. Bortan said.

ET, which affects up to 10 million people in the United States, is the most prevalent tremor disorder and among the most common neurological conditions. It is considered at least seven times more prevalent than PD, Dr. Bortan noted.

“Estimates of its prevalence vary widely because several other disorders, as well as certain medications, can result in similar tremors,” she said. “In addition, people with mild cases often do not seek medical attention, or the disorder may not be detected in clinical exams that do not include the particular circumstances in which an individual’s tremor occurs.”

One differentiator between the two disorders is when they start and how they progress. ET, according to Dr. Bortan, typically begins in middle age, although it can occur at any time, even in childhood. Its progression can vary. For some patients, it remains mild and doesn’t result in significant disability. In others, it progresses and can cause significant disability, making daily activities very difficult or impossible to complete.

In the case of PD, she said 60 years old is the average age of onset. In almost all patients, PD is a progressive disorder marked by increased disability over time.

The diseases also differ in how they affect the patient.

“ET most commonly affects the person’s hands, legs, head and voice, with tremor being the primary symptom,” Dr. Bortan noted. “In PD, the cardinal symptoms include slowness of movements, rigidity, tremor and gait and balance issues. It is also important to note that although it occurs in most people, tremor does not have to be present to make a diagnosis of PD.”

Both conditions can be affected by stress, anxiety and emotion.

“It is not uncommon to see an increase in tremor under stressful conditions,” Dr. Bortan said.

Linking the two – and the possibility that ET can progress to PD – is challenging and controversial among movement disorders specialists, she said, pointing to “inconsistent and unreliable diagnostic criteria.”

“There is evidence that some patients diagnosed with ET have an increased risk of developing PD years or decades after onset of action tremor,” she said.

This evidence includes:

  • Overlapping motor and non-motor features.
  • Relatively high (26 to 43 percent) prevalence of rapid eye movement sleep behavior disorder in ET patients.
  • Increased prevalence of PD in patients with longstanding ET.
  • Increased prevalence of ET in family members of patients with PD.
  • Presence of Lewy bodies, or clumps of proteins, in the brains of some ET patients (less than 25 percent).

“Yet, while a wealth of literature supports the relationship between ET and PD, the association is not yet fully defined or understood,” Dr. Bortan said.

Dr. Bortan is presenting a free webinar called “Understanding Essential Tremor” on Monday, March 26, from 5-6 p.m. To register, click here. Log-in information will be sent after registration.