Why is it important to know a patient's handedness (left or right) in neurology?

Importance of Handedness Assessment in Neurology

Determining a patient's handedness is critical in neurology because it helps predict cerebral dominance for language and motor functions, which directly impacts diagnosis, treatment planning, and prognosis for neurological conditions.

Cerebral Dominance and Language Localization

Handedness provides crucial information about brain lateralization and organization:

• Approximately 95% of right-handed individuals have left hemisphere language dominance
• Among left-handed people, language dominance is more variable: 73% have left hemisphere dominance, 15% have bilateral representation, and 27% have right hemisphere dominance 1
• The relationship between handedness and language dominance follows a linear pattern, with right-hemisphere language dominance increasing with the degree of left-handedness 1

Clinical Applications in Neurological Assessment

1. Stroke Management and Localization

• In acute ischemic stroke, knowing handedness helps predict the functional impact of lesions:
  • Dominant hemisphere strokes typically cause more severe language deficits
  • The NIHSS stroke scale specifically assesses motor function in both arms, where deficits in the dominant arm may have greater functional impact 2

2. Electroconvulsive Therapy (ECT) Planning

• For unilateral ECT, electrode placement is determined by cerebral dominance:
  • Electrodes are typically placed on the non-dominant hemisphere to minimize cognitive side effects
  • For right-handed patients, right unilateral ECT is standard
  • For left-handed patients, determining cerebral dominance is more complex and critical 2

3. Brain Arteriovenous Malformation (BAVM) Treatment

• Handedness information helps assess risk when BAVMs are located near eloquent cortex:
  • Treatment of lesions in the dominant hemisphere carries higher risk for language deficits
  • This information directly impacts surgical decision-making and risk assessment 2

4. Transcranial Stimulation Protocols

• For neuromodulation therapies like TMS or tES:
  • Laterality of stimulation may have different effects depending on handedness
  • Right-sided DLPFC stimulation may be more effective for certain conditions, but this effect may differ based on handedness 2

Neurobiological Basis

The neurobiological differences between right and left-handed individuals are significant:

• Right-handed individuals show stronger lateralization of motor control:

  • Dominant (right) hand is controlled primarily by the contralateral (left) hemisphere
  • Non-dominant hand shows more balanced bilateral control 3

• Left-handed individuals often demonstrate:

  • More balanced hemispheric involvement
  • Greater ipsilateral activation during motor tasks
  • More variable patterns of language lateralization 1

Assessment of Handedness in Clinical Practice

Comprehensive handedness assessment should include:

1. Hand preference inventories - Ask about preferred hand for:

   • Writing, throwing a ball, using scissors, knife and fork
   • Multiple activities provide more reliable assessment than writing hand alone 2, 4

2. Performance-based measures when necessary:

   • Finger tapping tests
   • Pegboard tasks
   • Grip strength measurements 4

Common Pitfalls to Avoid

• Relying solely on writing hand: Some individuals may have been forced to switch handedness for writing in childhood
• Overlooking mixed handedness: Some patients perform different tasks with different hands
• Failing to document handedness: This critical information should be part of every neurological examination
• Assuming cerebral dominance based on handedness alone: While correlated, the relationship is not absolute, especially in left-handed patients

By properly assessing and documenting handedness, neurologists can make more accurate predictions about brain organization, better localize neurological deficits, and optimize treatment approaches for their patients.