On May 6, Sen. Susan Collins, a Republican from Maine, revealed that she’s had a condition called essential tremor throughout the duration of her nearly 30-year Senate career and that she takes medication for it.

“I have had it for the entire time that I have served in the United States Senate,” Collins, 73, told News Center Maine. “It has absolutely no impact on my ability to do my job or on how I feel each day.” Collins recently announced in a video that she is running for a sixth term, and online comments called attention to the shakiness in Collins’ hands, voice, and head.

Collins' announcement comes as her Senate race is one of the most closely watched of this year's midterm elections, one in which concerns about her age is a factor for some voters. Last week, Maine Gov. Janet Mills, 78, suspended her Senate campaign, effectively ceding the fight for the Democratic nomination to political newcomer Graham Platner, who is 41. (Platner has spoken about his own health issues, including military-related disabilities such as PTSD, shoulder, and knee problems.)

This is the first time Collins has discussed her diagnosis publicly. “The tremor is occasionally inconvenient, and sometimes the subject of cruel comments online, but it does not hinder my ability to work,” she said in a statement to the Associated Press. 

We talked to experts about what to know about essential tremor, including how it’s different from Parkinson’s disease and how it’s treated.

What is essential tremor?

Essential tremor manifests most obviously as shakiness in both hands and arms. It can also affect a person's head, voice, or lower limbs.

It's "one of the most common neurological disorders," says Dr. Elan Louis, a neurologist at UT Southwestern Medical Center who researches essential tremor. “It's sort of a cousin, if you will, to Parkinson's disease," though the two present differently.

The tremor itself appears during activity rather than at rest. "The primary manifestation is a tremor that occurs when people are using their hands and their arms—so for example, while writing, while drinking from a cup, anything that involves hand usage," Louis says.

Dr. Albert Fenoy, director of functional neurosurgery at Northwell Health, describes it similarly: "It's a movement disorder that causes rhythmic involuntary shaking, most often in the hands when a patient's trying to move—so not at rest, but like an action- or an intention-type tremor." 

Symptoms can intensify in moments of stress or strong emotion, which is true across tremor disorders generally. That's part of why a doctor's exam doesn't always reflect a patient's typical day-to-day experience. "Classically, as a doctor, you go into the room: what you see for the first minute or two is often far worse than what the patient typically experiences on a day-to-day basis," Louis says.

Is essential tremor progressive?

Yes, but slowly—Louis says it worsens at a rate of about 1% to 2% per year, and not in a strictly linear way.

Fenoy describes how that progression typically unfolds. A patient may "start with a very fine tremor in their hands, maybe at a younger age," and over time the amplitude grows. "It just becomes larger, and it may even progress to other aspects of their body, not just their arms," he says. "It could go into their legs, but then it also comes into their head. The patient could have a head bob or even a jaw tremor, or it could even affect their voice." Where the tremor shows up, and how severely, varies from person to person.

How is essential tremor different from Parkinson’s?

The two conditions are often confused, but they show up differently—and essential tremor is far more common (and less serious). "It's as much as 20 times more common than Parkinson's disease," Louis says.

One difference is that while an essential tremor occurs during action, “the one in Parkinson's disease is a rest tremor because it occurs when the hands are resting in the lap or resting at someone's side," Louis says.

People with essential tremor have a 4 to 5 times higher risk of developing Parkinson's disease than the general population. But Louis emphasizes the absolute numbers stay low. "Any one of us has about a 0.5% to 1% risk of developing Parkinson's disease during our lifetime,” he says. “It just means essential tremor patients have a 2% to 4% chance of getting it, so the vast majority do not get Parkinson's disease.”

What causes essential tremor?

Researchers haven't pinned down a single cause. About 30% to 50% of cases run in families, but no strong genetic signal has emerged to explain the majority of cases.

What researchers have identified are degenerative changes in the cerebellum—the area at the back of the brain that helps coordinate movement. "Research that we and others have been doing for the last 10 or 20 years have identified degenerative changes in the cerebellum, which is an area of the brain that's sort of right at the back of the brain," Louis says. Specifically, a population of neurons called Purkinje cells appear to deteriorate, and experts believe that's the underlying driver of the tremor.

Age is the clearest risk factor. Essential tremor can show up at any age—Louis says he's seen it in 1-year-olds—but prevalence climbs steeply with each decade starting in a person’s 50s, 60s, and 70s. Fenoy adds that patients with a strong hereditary component "typically present at a much earlier age."

Does essential tremor affect cognitive ability?

There’s some disagreement in the field. For most of the time the disorder has been studied, it was viewed as a purely motor condition—and a relatively benign one. But among some experts, that picture is shifting.

"There's some emerging data over the last 10 to 20 years that patients with essential tremor can experience some mild cognitive difficulties," Louis says. Traditionally, the issues have involved executive function. "That's sort of being able to organize thoughts," he explains. More recent work, including studies from Louis' lab, has also found that some people with essential tremor have amnestic problems, meaning difficulties with memory.

Epidemiological studies also point to a roughly 50% to 100% higher risk of developing dementia among people with essential tremor, although evidence in this area is mixed. Louis stresses that the absolute risk remains low and that most patients won't develop dementia. "It's only recently that we're learning that there's a cognitive side—there can be, not that there is, but there can be a cognitive side to this illness," he says, adding that cognitive changes are "easily screenable” through neurologists’ suite of tests.

The shift in understanding has also affected how clinicians refer to the disorder. The condition was long called "benign essential tremor"—the terminology Collins used in her announcement of her diagnosis—but among medical professionals, the word "benign" has been dropped. "Patients don't like that term because it tends to minimize the problems that they have," Louis says.

How is essential tremor treated?

Most people with essential tremor never seek treatment at all. "Only about 10% of patients will seek treatment for this condition," Louis says, since symptoms are often mild enough to live with.

Fenoy notes that no medication targets tremor directly. Instead, the drugs commonly used are "geared to kind of slow down the nervous system"—typically a heart-rate-reducing medication and an anti-seizure medication. "They're good starting points. They don't work perfectly, and they also have associated side effects such as sedation or nausea," he says. A new drug is currently under review with the U.S. Food and Drug Administration, Louis notes, and early data looks “somewhat promising,” though it will be months before there's clarity on whether it's approved. 

Two procedures also exist. "There are two surgical treatments that are highly effective that give patients 70% to 90% reduction," Louis says. The first is a brain implant called deep brain stimulation, which has been performed for roughly 30 years. The second, focused ultrasound, is newer—about 5 to 10 years old in widespread practice. Combined, the two procedures have been performed on tens of thousands of patients worldwide, he says.

With deep brain stimulation—the "gold standard," Fenoy says—surgeons place an electrode deep in the brain, targeting a specific node in the faulty tremor circuit. "When we stimulate, it causes a functional block. It blocks that pathway with stimulated electricity, so we can block that pathway and we can take away that tremor." If the procedure is done on both sides of the body, "it affects both arms and actually stops tremor everywhere." The electrodes are connected by wires running down the neck to a pacemaker-like battery in the chest that powers the device.

The newer option, high-intensity focused ultrasound, is incisionless—no cutting required. "We focus ultrasound beams through the skull to create a lesion," Fenoy says. "We burn an area, the same target in the brain where we put an electrode, and instead of doing surgery, we just kind of make a roadblock by burning that tissue, destroying it. That takes away tremor as well." It's used for tremor on one side of the body, but it's "extremely effective,” he adds.

How does essential tremor affect quality of life?

For many patients, the hardest part of essential tremor isn't physical, but social. "Patients have social stigmatism” because their symptoms sometimes interfere with spending time with friends,  Fenoy says. The shame and self-consciousness of visible shaking can lead people to withdraw from the meals, gatherings, and small daily rituals that anchor a social life. In his experience with patients, after surgical treatment, "their socialization dramatically improves,” he says. “It's definitely a quality-of-life procedure."

Patients typically pursue treatment for one of two reasons, Louis says: "The two things that drive a desire to be treated on the patient's part are embarrassment, and also functional difficulty. "Essential tremor most often affects the hands, but it can also affect the head and voice. Katharine Hepburn's quavering voice and head tremor in the film On Golden Pond is a classic example, Louis notes—"that characteristic quaver to the voice was part of the tremor that Katharine Hepburn had."

For people whose careers depend on fine-motor control, the condition can be career-altering. "I've had patients over the years who are dentists, physicians, artists, jewelers, people that really need fine use of their hands, and it's difficult," Louis says. Treatment can sometimes restore function, though musicians in particular often struggle to return to their previous level of precision.

Essential-tremor patients can also develop some other neurological symptoms, but they tend not to be severe. Some people experience slight gait ataxia, meaning a bit of unsteadiness while walking, "but it's generally very mild, and it's not something that really requires that they use a cane or even that they end up in a wheelchair," Louis says.

Why isn’t essential tremor talked about more?

Despite being the most common movement disorder, essential tremor flies under the radar—and Fenoy says the reasons are partly cultural. "People think, as you get older, you start having shaking,” he says. “Historically people will be like, 'Oh, my grandmother has shaking, she had tremor. I'm probably going to have it too.' And people think there's nothing to do about it,” but treatments have greatly evolved.

Fenoy's bottom line for patients: Essential tremor doesn't have to be something you simply put up with. "This is a disease that's benign, so it's not going to kill you, but it bothers patients, and they don’t have to live this way. If their quality of life is suffering, there's something to do about it."