What is the difference between essential tremor and Parkinson's disease?

From the Guidelines

Essential tremor and Parkinson's disease are distinct neurological disorders with different characteristics, though they can sometimes be confused, and the most recent evidence suggests that essential tremor primarily causes action tremors, while Parkinson's disease features resting tremors with additional hallmark symptoms. Essential tremor primarily causes action tremors that occur during voluntary movement, particularly affecting the hands, head, and voice, as noted in a study on beta-blocker treatment for essential tremor 1. These tremors typically worsen when performing tasks like holding a cup or writing. In contrast, Parkinson's disease features resting tremors that are most noticeable when the affected body part is relaxed and supported, along with additional hallmark symptoms including bradykinesia (slowness of movement), rigidity, and postural instability, as described in a study on Parkinsonian syndromes 1. The tremor in Parkinson's often presents as a "pill-rolling" motion between the thumb and forefinger.

Key Differences

• Essential tremor usually progresses slowly and may respond to medications like propranolol (20-320 mg daily) or primidone (50-250 mg daily) 1.
• Parkinson's disease requires dopaminergic treatments such as levodopa-carbidopa (starting at 25/100 mg three times daily) 1.
• Essential tremor has a strong genetic component with about 50% of cases being familial, whereas Parkinson's disease involves the degeneration of dopamine-producing neurons in the substantia nigra of the brain, with most cases being sporadic.
• Alcohol temporarily improves symptoms in many essential tremor patients but has no beneficial effect on Parkinsonian tremor, which can be a useful diagnostic distinction.

Diagnostic Considerations

A recent study on 22q11.2 deletion syndrome highlights the importance of periodic neurologic enquiry/assessments for seizures/seizure-like episodes and cardinal motor features of PD or other movement disorders, supplemented by standardized rating scales and ancillary procedures 1. When diagnostic uncertainty exists, dopaminergic imaging (when available) may assist in differentiating drug-induced from neurodegenerative parkinsonism. The most critical aspect of managing these conditions is early and accurate diagnosis, followed by tailored treatment to improve morbidity, mortality, and quality of life.

From the FDA Drug Label

Parkinson’s disease is a progressive, neurodegenerative disorder of the extrapyramidal nervous system affecting the mobility and control of the skeletal muscular system. Its characteristic features include resting tremor, rigidity, and bradykinetic movements. The UPDRS is a multi-item rating scale intended to evaluate mentation (Part I), activities of daily living (Part II), motor performance (Part III), and complications of therapy (Part IV). Part III of the UPDRS contains 14 items designed to assess the severity of the cardinal motor findings in patients with Parkinson’s disease (e.g., tremor, rigidity, bradykinesia, postural instability)

The main difference between essential tremor and Parkinson's disease is that Parkinson's disease is a progressive neurodegenerative disorder characterized by:

• Resting tremor
• Rigidity
• Bradykinetic movements In contrast, essential tremor is not explicitly described in the provided drug labels, but it can be inferred that it is a different condition, as Parkinson's disease has distinct characteristic features. 2 3

From the Research

Differences between Essential Tremor and Parkinson's Disease

• Essential tremor (ET) is usually characterized by symmetric bilateral postural and kinetic tremor, which may respond to low alcohol consumption 4.
• In contrast, the typical tremor form of Parkinson's disease (PD) is an asymmetric rest tremor, which is treated with dopaminergic agents such as levodopa 4.
• ET tremor may be controlled with medical treatment using primidone or beta-blockers, while PD is treated with dopaminergic agents 4.

Diagnostic Challenges

• Distinguishing essential tremor from Parkinson's disease can be challenging, both in the early stages of these diseases and as these diseases progress 5.
• Various tremor types (rest, postural, kinetic and intention) may be seen in both essential tremor and Parkinson's disease, making diagnosis difficult 5.
• Laboratory testing, such as accelerometry and surface electromyography, spiral analysis, dopamine transporter imaging, olfactory testing, and postmortem histopathology, may provide information to aid in differentiating the two diseases 5.

Relationship between Essential Tremor and Parkinson's Disease

• There is evidence to suggest a link between essential tremor and Parkinson's disease, with some patients having a combination of long-standing ET with subsequent PD (ET-PD) 6.
• Patients with essential tremor are at higher risk to develop Parkinson's disease, and features such as constipation and anosmia may be more common in ET-PD patients 7.
• The co-occurrence of essential tremor and Parkinson's syndrome variants, including PD, has been observed in clinicopathological studies 8.

Clinical Features and Diagnosis

• ET-PD and ET-plus (parkinsonism) can be clinically difficult to differentiate due to overlapping motor and non-motor features 7.
• Dopamine transporter (DAT) scans and levodopa trials may be valuable in clarifying the diagnoses of ET-PD and ET-plus (parkinsonism) 7.
• The diagnosis of parkinsonism is made when bradykinesia, rigidity, and resting tremor are all clinically evident, and may co-occur with essential tremor 8.