How Is Parkinson's Diagnosed vs. Essential Tremor?

Doctors differentiate Parkinson’s disease from Essential Tremor primarily by observing when the shaking happens and looking for other subtle physical signs. Parkinson’s typically causes a “resting tremor” that occurs when your muscles are completely relaxed ^[1], whereas Essential Tremor usually causes an “action tremor” that happens when you are actively moving or holding a posture ^[2]. While many patients receive a diagnosis right there in the office based on a physical exam alone, doctors will sometimes use a specialized imaging test called a DaTscan to look for the specific loss of dopamine-producing cells that defines Parkinson’s ^[3].

The Physical Exam: Clues in How You Move

A movement disorder specialist can often tell the difference between these two conditions simply by having you perform a series of simple tasks in the clinic. They are looking for specific patterns in your tremor, your physical movements, and your medical history.

Resting vs. Action Tremors

The most defining characteristic of a Parkinson’s tremor is that it happens at rest. This means your hand might shake while it is lying completely relaxed in your lap ^[1]. This is often described as a “pill-rolling” tremor, as it can look like you are rolling a small object between your thumb and index finger ^[2].

Essential Tremor, on the other hand, is an action or postural tremor ^[4]. It typically becomes noticeable when you use your hands to do something, like pouring a glass of water or holding your arms outstretched ^[1]. During your exam, the doctor might ask you to draw an Archimedes spiral on a piece of paper. Essential Tremor usually causes large, shaky spirals, while Parkinson’s often leads to progressively smaller, cramped handwriting (a symptom called micrographia).

Sometimes, Parkinson’s patients develop what is known as a re-emergent tremor ^[5]. When they hold their arms out, their tremor stops momentarily, but starts up again after a short delay of a few seconds ^[2]. This latency helps doctors identify Parkinson’s, as an Essential Tremor usually begins immediately upon holding a posture ^[6].

Asymmetry vs. Symmetry

Parkinson’s symptoms almost always begin on one side of the body and remain more pronounced on that side over time ^[1][7]. Essential Tremor tends to be symmetric, affecting both sides of the body relatively equally from the start ^[4]. Essential Tremor is also more likely to cause your head or voice to shake, which is less common in early Parkinson’s ^[8].

Clues in Your History

Before examining your physical movements, your doctor will ask about your history. Essential Tremor often runs strongly in families and frequently improves temporarily after drinking a small amount of alcohol—two classic clues that help rule out Parkinson’s.

Looking Beyond the Tremor

Because tremor is the most visible symptom, it’s easy to focus solely on the shaking. However, doctors diagnosing Parkinson’s will look for its other hallmark physical signs, which are absent in Essential Tremor ^[9]. These include:

• Bradykinesia: An abnormal slowness of movement, often checked by having you rapidly tap your fingers or stomp your foot ^[10].
• Rigidity: A distinct stiffness in the limbs when the doctor moves your arm or leg ^[11]. You might experience this simply as tight, achy muscles.
• Non-motor symptoms: Parkinson’s affects the nervous system throughout your entire body, not just your movement. Because of this, doctors will often ask about issues like acting out dreams (REM sleep behavior disorder), loss of smell, or chronic constipation, which are strongly linked to Parkinson’s ^[12][13].

The DaTscan: Confirming Dopamine Loss

Sometimes, clinical symptoms overlap or are difficult to read. In these cases, a neurologist may order a DaTscan (Ioflupane I-123 SPECT). This is an imaging test that allows doctors to see the dopamine system inside your brain ^[14].

The DaTscan involves receiving an intravenous (IV) injection of a safe radioactive tracer that binds to dopamine transporters. After waiting a few hours for the tracer to reach your brain, you will lie still in a specialized scanner (similar to an MRI, but open rather than an enclosed tube) for about 30 to 45 minutes while a camera takes images of your brain.

Parkinson’s disease is caused by the progressive loss of dopamine-producing brain cells. If you have Parkinson’s, the scan will show a distinct pattern of dopaminergic deficiency ^[3][15]. If you have Essential Tremor, your dopamine system is perfectly intact, and the scan will appear normal ^[3].

It is important to tell your doctor about all the medications you are taking before having a DaTscan. Certain antidepressants and other medications (like bupropion or venlafaxine) can interfere with the scan and cause false-positive results ^[16][17].

While the DaTscan is excellent at separating Parkinson’s from Essential Tremor, it cannot differentiate Parkinson’s from other rare “atypical parkinsonian” syndromes that also involve dopamine loss ^[18][19].

Emerging Imaging Tools

Researchers are constantly developing new ways to diagnose movement disorders. Advanced MRI techniques are being used to detect a specific feature in the brain called the “swallow tail sign” ^[20]. This refers to the shape of a cluster of healthy cells in the brain. The absence of this normally occurring, healthy brain feature is a highly accurate marker for Parkinson’s disease compared to Essential Tremor ^[21][22]. While these tools are promising, they are currently used as complements to, rather than replacements for, clinical exams and DaTscans ^[1][23].