What are the different types of tremors and how are they differentiated?

Tremor Classification and Differentiation

Tremors are classified primarily by their activation condition (rest vs. action), frequency, and associated clinical features, which directly guides diagnosis and treatment to improve patient quality of life.

Primary Classification Framework

Tremors are categorized based on when they occur and their clinical context, which is more diagnostically useful than patient descriptors alone 1, 2:

Rest Tremor

• Parkinsonian tremor is the hallmark rest tremor, occurring when the affected body part is relaxed and supported against gravity 1
• Characterized by 4-6 Hz frequency with a classic "pill-rolling" appearance in the hands 1, 3
• Typically asymmetric at onset, affecting one side more than the other, and must be accompanied by other parkinsonian features (bradykinesia, rigidity, postural instability) for diagnosis 1
• Can have postural and kinetic components, creating diagnostic overlap with other tremor types 4

Action Tremors

Action tremors subdivide into postural, kinetic, and intention tremors 2:

Postural/Kinetic Tremor

• Essential tremor is the most common pathologic tremor, affecting 0.4-6% of the population, presenting as both postural and kinetic tremor with 4-8 Hz frequency 3, 2
• Primarily involves upper extremities and head, transmitted in autosomal-dominant fashion in 50% of cases 3
• Enhanced physiologic tremor appears similar but is triggered by anxiety, medications, caffeine, or fatigue 2

Intention Tremor (Cerebellar)

• Becomes more pronounced during goal-directed movements, particularly evident during finger-to-nose testing with a coarse, irregular "wing-beating" appearance 1, 4
• Associated with dysarthria and ataxic gait, which distinguishes it from other tremor types 1, 4
• Does not stop with distraction, unlike functional tremor 5

Key Differentiating Features

Functional (Psychogenic) Tremor

• Characterized by variability in frequency and amplitude, and most importantly, distractibility (stopping when attention is redirected) 5
• Not a diagnosis of exclusion—requires demonstration of specific clinical signs including abrupt onset, spontaneous remission, changing characteristics, and extinction with distraction 5, 2

Dystonic Tremor

• Irregular and position-specific, often affecting isolated body parts 4
• Isolated head tremor is more likely dystonic than essential tremor 6

Asterixis ("Flapping Tremor")

• Technically a negative myoclonus rather than true tremor, seen in hepatic encephalopathy 1, 4

Diagnostic Algorithm

Step 1: Determine activation condition

• Does tremor occur at rest (suggests Parkinson's disease) or with action (suggests essential tremor, cerebellar, or enhanced physiologic tremor)? 2, 7

Step 2: Assess frequency and amplitude

• 4-6 Hz rest tremor = Parkinsonian 1, 3
• 4-8 Hz postural/kinetic = Essential tremor 3
• Coarse, irregular with intention = Cerebellar 1, 4

Step 3: Evaluate associated features

• Bradykinesia, rigidity, postural instability = Parkinson's disease 1
• Dysarthria, ataxic gait = Cerebellar pathology 1, 4
• Distractibility, variability = Functional tremor 5

Step 4: Consider advanced testing when clinical diagnosis is unclear

• Ioflupane SPECT/CT (DaTscan) differentiates Parkinsonian tremor from essential tremor by demonstrating dopaminergic deficiency 1
• MRI and functional neuroimaging help identify structural lesions causing cerebellar tremor 1

Critical Pitfalls

• Do not diagnose essential tremor in patients with isolated head tremor—this is more likely dystonic 6
• Avoid labeling functional tremor as diagnosis of exclusion—actively demonstrate positive signs of distractibility and variability 5, 2
• Recognize that Parkinsonian tremor can have postural components, creating a diagnostic grey zone with essential tremor when mild parkinsonian signs coexist 4, 7
• Consider Wilson's disease and fragile X-associated tremor/ataxia syndrome in younger patients with tremor, as these are treatable conditions that must not be missed 7