What is dysmetria?

Dysmetria: Definition, Causes, and Clinical Significance

Dysmetria is the inability to accurately judge distance and range in movements, resulting in over-reaching (hypermetria) or under-reaching (hypometria) a target, affecting limbs, speech, and eye movements. 1

Clinical Features and Assessment

• Dysmetria is a cardinal sign of cerebellar dysfunction, characterized by impaired ability to measure distance in muscular movements 2, 1
• It can manifest as either hypermetria (overshooting the target) or hypometria (undershooting the target) during goal-directed movements 3
• Clinical assessment is typically performed through:
  • Finger-to-nose test: patient alternately touches their nose and the examiner's finger 1
  • Heel-to-shin test: patient slides heel down the opposite shin 1
  • Rapid alternating movements: to assess coordination and accuracy 2

Pathophysiology

• Dysmetria results from impairment in the predictive computation of voluntary movements within the cerebellum 4
• The cerebellum normally maintains an internal forward model that predicts current and future body states by integrating previous state estimates with motor command copies 4
• In cerebellar disorders, there is an imbalance between the timing and/or intensity of agonist and antagonist muscle activities 5, 6
• EMG studies show that hypermetria is associated with:
  • Delayed onset of antagonist muscle activity
  • Prolonged agonist activity
  • Abnormal gradual buildup of agonist activity 6

Common Causes

• Cerebellar lesions (stroke, hemorrhage, tumors) 1
• Spinocerebellar ataxias and other neurodegenerative disorders 1
• Multiple sclerosis affecting cerebellar pathways 5
• Multiple system atrophy (MSA) can cause a shift from hypermetria to hypometria as the disease progresses 5
• Paraneoplastic cerebellar degeneration 1
• Congenital cerebellar malformations 1
• In children, cerebellar hypoplasia (e.g., due to in utero infections) 3

Clinical Significance

• Dysmetria is a key component of ataxia syndromes 2
• It affects activities of daily living by impairing coordination of movements 7
• The presence of dysmetria can help localize neurological lesions to the cerebellum or its pathways 2, 1
• In children, persistent dysmetria may be a "red flag" warranting prompt referral, especially if accompanied by loss of motor milestones 2
• Dysmetria of eye movements (ocular dysmetria) can also occur, manifesting as overshooting or undershooting during saccades 2

Diagnostic Approach

• MRI is the preferred imaging modality for evaluating dysmetria, as it can identify underlying structural abnormalities in the cerebellum, brainstem, or cerebellar pathways 1
• Brain imaging helps identify cerebellar lesions, congenital malformations, and evidence of neurodegenerative processes 1
• In cases of rapidly progressive symptoms, additional workup may be needed to rule out treatable causes 2

Management

• Treatment focuses primarily on addressing the underlying cause 1
• Rehabilitative approaches include:
  • Occupational therapy to improve accuracy of movements 1
  • Physical therapy for balance and coordination 1
  • Task-specific training to improve movement precision 1
• There are currently no specific pharmacological treatments directly targeting dysmetria 1
• Prognosis depends on the underlying cause - symptoms may improve if the cause is treatable, while chronic progressive symptoms may indicate neurodegenerative processes with poorer long-term outcomes 1