How do you differentiate and treat essential tremor vs Parkinson's disease?

Differentiating Essential Tremor from Parkinson's Disease

Essential tremor presents as bilateral action tremor of the upper limbs, while Parkinson's disease begins unilaterally as a rest tremor accompanied by bradykinesia and rigidity. 1

Clinical Differentiation

Tremor Characteristics

Essential Tremor:

• Bilateral action tremor affecting hands and arms 1
• Occurs during voluntary movement (postural and kinetic tremor) 2
• Frequency typically 4-12 Hz 2
• Handwriting is tremulous but normal-sized 1
• No neurological signs beyond tremor 1

Parkinson's Disease:

• Unilateral onset, asymmetric presentation 1
• Rest tremor (occurs when limb is at rest) 1
• Frequency typically 4-6 Hz 2
• Handwriting is small (micrographic) but non-tremulous 1
• Always accompanied by bradykinesia and rigidity 1

Key Distinguishing Features

The handwriting test is particularly valuable: In PD, writing is small and cramped without tremor, whereas in ET, writing is tremulous but maintains normal size 1. This bedside test can usually distinguish the two conditions reliably.

Non-motor symptoms help differentiate ET-PD from ET-plus with parkinsonism:

• Constipation is present in 73% of ET-PD cases versus 33% in ET-plus 3
• Anosmia occurs in 48% of ET-PD cases versus 19% in ET-plus 3
• These prodromal features suggest true PD pathology 3

Associated Clinical Signs

Parkinson's Disease includes:

• Bradykinesia (slowness of movement) 1
• Rigidity (increased muscle tone) 1
• Postural instability 4
• Resting tremor that improves with action 1

Essential Tremor features:

• Isolated tremor without other parkinsonian signs 1
• Progressive bilateral action tremor 5
• May affect voice and head in addition to limbs 5

Diagnostic Testing

When clinical examination is inconclusive, dopamine transporter (DAT) imaging provides objective differentiation: DAT scans show reduced uptake in PD but remain normal in ET 3. This test is particularly valuable when patients present with overlapping features 3.

Additional diagnostic tools include:

• Accelerometry and surface electromyography to characterize tremor patterns 2
• Spiral analysis to assess tremor amplitude and frequency 2
• Olfactory testing (impaired in PD, normal in ET) 2, 3

Treatment Approaches

Essential Tremor Treatment

First-line pharmacological therapy:

• Propranolol 80-240 mg/day is the most established treatment, effective in up to 70% of patients 6, 7
• Primidone is equally effective as first-line therapy, though benefits may take 2-3 months to appear 6, 7
• Initiate treatment only when tremor interferes with function or quality of life 6, 7

Important contraindications for propranolol:

• Chronic obstructive pulmonary disease 6, 7
• Bradycardia 6, 7
• Congestive heart failure 6, 7

For medication-refractory cases:

• MRgFUS thalamotomy shows 56% sustained tremor improvement at 4 years with lower complication rates (4.4%) compared to DBS (21.1%) 6, 7
• Deep brain stimulation is preferred for bilateral tremor or younger patients requiring adjustable treatment 6

Parkinson's Disease Treatment

Levodopa remains the gold standard:

• Levodopa crosses the blood-brain barrier and converts to dopamine, relieving parkinsonian symptoms 4
• Carbidopa is combined with levodopa to reduce peripheral conversion, allowing 75% dose reduction and decreasing nausea 4
• The plasma half-life increases from 50 minutes to 1.5 hours when carbidopa is added 4

Dopamine agonists as alternative:

• Ropinirole demonstrated efficacy in both early and advanced PD 8
• In early PD trials, 71% of patients responded versus 41% on placebo 8
• Mean improvement in UPDRS motor scores was statistically significant 8

Critical Pitfalls to Avoid

Beware of coexisting conditions: ET and PD can coexist in the same patient over time 9, 10. All common variants of parkinsonism (PD, PSP, MSA) have been documented to co-occur with ET 9.

Do not rely solely on tremor characteristics: Various tremor types (rest, postural, kinetic, intention) may be seen in both conditions, particularly as diseases progress 2. The presence of bradykinesia and rigidity is essential for PD diagnosis 1.

Levodopa trial considerations: 91% of ET-PD patients receive levodopa trials versus only 21% of ET-plus cases 3. A positive response to levodopa strongly supports PD diagnosis, though lack of response does not exclude it.

Monitor for sudden onset of sleep: Levodopa can cause sudden sleep episodes during activities of daily living, occurring up to one year after treatment initiation 4. Patients should be counseled about driving risks and questioned specifically about drowsiness 4.