Etiology of Intentional Tremor
Intentional tremor primarily results from damage to the cerebellum or its connections, including the midbrain, thalamus, and cerebellar pathways, which can be caused by various neurological disorders, vascular events, or neurodegenerative diseases.
Definition and Characteristics
- Intentional tremor is characterized by a tremor that worsens as the affected limb approaches a target during voluntary movement, often accompanied by postural tremor components 1
- It is frequently described as a coarse, irregular tremor that becomes more pronounced during goal-directed movements 2
- The classical appearance is a "wing-beating" appearance, particularly evident during finger-to-nose testing 2
Primary Etiologies
Cerebellar Disorders
- Cerebellar damage is the most common cause of intentional tremor, affecting the coordination of movement and resulting in dysmetria 1
- Cerebellar tremor can present not only as intention tremor but also as postural, kinetic, and even rest tremor in some cases 1
- Specific cerebellar conditions include:
Vascular Causes
- Cerebellar strokes can cause intentional tremor as part of a broader cerebellar syndrome 1
- Midbrain strokes affecting the red nucleus and surrounding structures can lead to a particularly treatment-resistant form of tremor 3
- Thalamic strokes or hemorrhages can disrupt cerebellar outflow pathways 3
- Frontal cortical infarcts may rarely cause contralateral postural and intentional tremor by interrupting inhibitory fronto-subcortical motor circuits 4
Neurodegenerative Disorders
- Wilson's disease presents with a characteristic tremor as part of its neurological manifestations, classified as a "pseudosclerosis dominated by tremor" 2
- Essential tremor can progress to include intentional components in approximately 25% of patients, particularly in older individuals 5
- Multiple sclerosis can cause intentional tremor due to demyelinating lesions in cerebellar pathways 2
Other Causes
- Traumatic brain injury affecting the cerebellum or its connections 2
- Drug-induced tremor (certain medications can cause or exacerbate intentional tremor) 2
- Toxic exposures affecting cerebellar function 2
Pathophysiology
- Intentional tremor results from disruption of the cerebello-thalamo-cortical pathways 6
- The cerebellum normally provides timing signals for the initiation and termination of movements 1
- Damage to these pathways leads to errors in movement prediction and correction 1
- In some cases, combined dysfunction of multiple brain regions (cerebellum, thalamus, and basal ganglia) contributes to complex tremor syndromes like Holmes tremor 6
Clinical Correlations
- Intentional tremor is often accompanied by other signs of cerebellar dysfunction:
- The presence of these associated signs helps distinguish cerebellar tremor from other tremor types 2
- Quantitative analysis shows that patients with intentional tremor demonstrate increased curvature during the deceleration and target phase of movement, along with hypermetria 5
Differential Diagnosis
- Parkinsonian tremor (primarily a rest tremor, but can have postural and kinetic components) 2
- Dystonic tremor (irregular, often position-specific) 2
- Hepatic encephalopathy (asterixis or "flapping tremor" - technically a negative myoclonus) 2
- Psychogenic tremor (variable frequency, distractible) 2
Common Pitfalls in Diagnosis
- Mistaking intentional tremor for other tremor types, particularly in mixed tremor syndromes 1
- Overlooking underlying causes such as Wilson's disease, which requires specific treatment 2
- Failing to recognize that intentional tremor can develop as a later manifestation of essential tremor 5
- Attributing intentional tremor to aging or anxiety without proper neurological evaluation 2