The world of tremors is filled with mysteries and puzzles. Not even the best medical professionals can unravel every person’s unique situation. According to one source, general neurologists treating tremor have a diagnostic error rate of 25% to 35%.ⁱ This is partly due to the fact that there are different categories of tremors, and there is overlap among the various conditions with which they are associated.

How are tremors classified?

The human brain appears to be hardwired to put things into categories. For example, you would probably put a poodle and a beagle in one category (dogs), and a hammer and a screwdriver in another (tools), but you would be unlikely to put a poodle and a hammer in the same category. These examples are pretty clear, but it’s murkier with tremors.

Tremors are often categorized according to location (hand, head, voice, legs, etc.), appearance (amplitude or range of motion, and frequency or speed), and occurrence (resting or action).

Unlike resting tremors, which occur involuntarily even when the hand or limb is at rest, action tremors happen when a person moves a muscle or group of muscles voluntarily, as in reaching for an object. Action tremors are further classified into subcategories:

• Postural tremors happen when holding a position or posture against gravity, as outstretched arms
• Kinetic tremor occurs with any voluntary movement, such as hand clapping
• Intention tremor begins with purposeful movement toward a target, such as switching on a lamp, and may worsen closer to the target
• Task-specific tremor occurs during specific goal-oriented tasks such as handwriting
• Isometric tremor is involved with maintaining a muscle contraction such as holding a heavy book.

Tremor categories associated with a disease or condition

Another way to categorize tremors is by determining if they are associated with an underlying disease, condition, exposure to medication or substance, etc. The National Institute of Neurological Conditions and Stroke identifies seven common classifications of tremor, though there are about 13 more less common tremor categories:

1. Essential tremor is the most common movement disorder. There is known cause, but roughly half of cases have a family history. Though ET can begin at any age, most people don’t develop tremors until midlife or later. While ET can remain mild for many years, it tends to worsen and become more pronounced over time so it is considered progressive but not life-threatening. Most often it affects both hands, or the head or voice.
2. Dystonic tremor is linked with a condition called dystonia, characterized by overactive muscles that can spasm or cramp painfully. It is marked by abnormal posture and sustained jerky, involuntary movements. It can mimic the type of resting tremor seen in Parkinson’s disease.
3. Cerebellar tremor is the result of damage to cerebellum (part of the brain that affects motor control and balance) or other movement pathways in the brain. It is a low frequency (slow) but high amplitude (noticeable range of motion) and tends to happen toward the end of a voluntary movement like switching on a table lamp.
4. Psychogenic tremor is often associated with a psychiatric disorder such as depression, anxiety or post-traumatic stress disorder. It can affect any body part and begin suddenly especially in times of stress. One prominent characteristic is that it will decrease or disappear if the person is distracted.
5. Physiologic tremor is something that most likely all of us have. It is usually completely unnoticeable, most often affecting the hands and fingers.
6. Enhanced physiologic tremor is distinctly noticeable. It can be caused by a reaction to medications or other substances, alcohol withdrawal, or things like thyroid or blood sugar conditions. It generally goes away once the cause is removed.
7. Parkinsonian tremor is a resting tremor due to Parkinson’s disease or a condition called Parkinsonism. It mostly affects one or both hands at rest but can progress to other parts of the body.

Matching tremor to treatment

It is very important to identify the type of tremor and whether or not it’s due to a disease or other condition. It is frustrating and demoralizing for patients to be mis-diagnosed, not to mention misunderstood. It is draining to see numerous doctors and specialists over many long months or years, and to try drug after drug unsuccessfully.

Fortunately, for persons with Essential Tremor, an exciting new treatment called MRI-guided Focused Ultrasound (MRgFUS) can control tremors in the dominant hand during a single outpatient procedure. Focused Ultrasound is an FDA-approved noninvasive treatment that uses over 1,000 “beams” of ultrasound to cut off abnormal signals in the brain before they can reach the hand. Learn more about MRgFUS or contact Sperling Neurosurgery Associates for a consultation.

ⁱhttps://www.essentialtremor.org/wp-content/uploads/2013/07/FactSheet012013.pdf