3 Types of Tremor (And Why It's Not Automatically Parkinson's)
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A caregiver messaged us after her son's brain injury, worried he was developing Parkinson's disease at 24. His hand had started shaking, worse whenever he reached for something, steady when his hand was resting in his lap.
That detail, worse with reaching and steady at rest, turned out to matter more than the shaking itself. What she was describing wasn't Parkinsonian tremor at all. It was a different type entirely, and it pointed doctors toward a different part of the brain.
What Tremor Actually Is
Tremor is a symptom, not a diagnosis on its own. It's defined clinically as an involuntary, rhythmic, back-and-forth movement of a body part, and it shows up across a wide range of conditions, including Parkinson's disease, multiple sclerosis, stroke, and traumatic brain injury.
The current classification system, published by the International Parkinson and Movement Disorder Society in 2018, sorts tremor along two lines: what it looks like clinically, and what's causing it underneath. That distinction is exactly why the same word, tremor, can mean very different things depending on the type.
Three types come up most often in families dealing with a brain condition: essential tremor, Parkinsonian tremor, and cerebellar tremor. They can look similar at a glance. The details that separate them, when the shaking happens, where it happens, and how it responds to movement, are what actually tell you which one you're looking at.
Essential Tremor
Essential tremor typically shows up in both hands at once, and it appears during action or while holding a posture, reaching for a cup, holding a spoon steady, not while the hand is at rest. It usually starts in the hands and can later involve the head or voice.
It's often genetic. Somewhere between 50 and 70 percent of cases run in families, and in those cases it tends to start earlier in life. Small amounts of alcohol often temporarily ease essential tremor, which is one of the clinical clues doctors ask about directly.
It's the most common cause of this kind of action-based tremor, and on its own it isn't a sign of a more serious progressive brain disease.
Parkinsonian Tremor
Parkinsonian tremor looks almost opposite in its timing. It shows up at rest, when the hand is relaxed and unsupported, and it often eases up once the person starts using that hand on purpose. The classic description is a "pill-rolling" motion of the thumb and fingers.
It usually starts on one side of the body before the other, and it rarely travels alone. It tends to appear alongside other signs of parkinsonism, slowness of movement, and rigidity, rather than as an isolated symptom.
That combination, resting tremor plus those other movement changes, is what separates Parkinsonian tremor from essential tremor, more than the shaking pattern by itself.
Cerebellar Tremor
Cerebellar tremor is the one most directly relevant to brain injury, because it comes from damage to the cerebellum itself, or the pathways connecting it to the rest of the brain, exactly the kind of damage that can happen in a TBI, a stroke, or conditions like multiple sclerosis.
This tremor shows up during purposeful movement and gets worse the closer the hand gets to its target, reaching for a doorknob and shaking more as the hand approaches it, not less. It's typically slower and larger in amplitude than the other two types, and it often comes with other cerebellar signs, like unsteady walking or trouble judging distance with the hands.
This was the type in that caregiver's son.
Why the Distinction Matters
Getting the type right changes where the workup goes next. A resting tremor points toward parkinsonism. An action tremor that worsens on approach to a target points toward the cerebellum, which, after a brain injury, can mean looking specifically at that part of the injury rather than assuming a new, unrelated diagnosis.
It's worth saying plainly that even essential tremor, the most common type, isn't fully settled science. The 2018 classification itself notes that essential tremor may not be a single disease, but a family of related conditions that happen to share the same core pattern. Researchers are still working out where those lines fall.
That mother wasn't wrong to be worried. She was watching something real change in her son's body. She just needed the right questions to bring to his neurologist, timing, location, what makes it better or worse, and those three details did more work than any amount of general worry could.
Source: Bhatia, K.P., et al. (2018). Consensus Statement on the classification of tremors. From the task force on tremor of the International Parkinson and Movement Disorder Society. Movement Disorders, 33(1), 75-87.