Why is handedness important in neurology?

Why Handedness is Critical in Neurological Assessment

Handedness assessment is essential in neurology because it predicts hemispheric dominance for language and verbal memory, which directly determines treatment risk and surgical planning, particularly when lesions affect the dominant hemisphere. 1, 2

Primary Clinical Significance: Predicting Language Lateralization

The fundamental importance of handedness lies in its correlation with cerebral dominance:

• All right-handed individuals (100%) lateralize language functions to the left hemisphere 2, 3
• Only 70% of left-handed individuals have left hemisphere language dominance, with 15% showing bilateral representation and 15% demonstrating right hemisphere language superiority 2, 3
• This variability in left-handed patients creates critical uncertainty when planning interventions that could affect language areas 3

Impact on Treatment Risk Assessment

Surgical Planning for Brain Lesions

When evaluating arteriovenous malformations (BAVMs) or other structural lesions, handedness allows estimation of hemispheric dominance, which directly influences treatment risk 1:

• Lesions in the dominant hemisphere carry higher risk of language deficits post-intervention 1
• The side of the lesion must be interpreted in context of handedness to accurately predict functional outcomes 1
• This risk stratification is mandatory for informed consent and surgical decision-making 1

Neurosurgical Candidacy Determination

Comprehensive neurological assessment including handedness determination is required before any functional neurosurgery procedure 4:

• Multidisciplinary teams must assess hemispheric dominance as part of the risk-benefit analysis 4
• Structural brain anomalies on MRI must be interpreted relative to the patient's dominant hemisphere 4

Proper Assessment Methodology

Multi-Activity Inquiry Approach

The most appropriate neurological test for determining handedness involves inquiring about preferred hand use for multiple skilled activities—including throwing a ball, using scissors, knife and fork, and writing—rather than relying on writing hand alone 3:

• Writing hand preference alone is insufficient and represents a common clinical error 3
• Multi-activity assessment provides more accurate determination of true cerebral dominance 3
• The Edinburgh Handedness Inventory or similar comprehensive tools should be used 5

Standardized Testing Options

For situations requiring formal assessment, the Duke University Medical Center ECT Cerebral Dominance Test or similar protocols may be employed 3

Understanding Hemispheric Specialization

Dominant Hemisphere Functions (Usually Left)

The hemisphere predicted by handedness controls critical functions 2:

• Speech production (Broca's area) and comprehension (Wernicke's area) 2
• Reading and writing abilities 2
• Verbal memory systems 2
• Morphosyntactic processing (grammar and sentence structure) 2

Non-Dominant Hemisphere Functions (Usually Right)

Understanding which hemisphere is non-dominant also matters clinically 2:

• Spatial cognition and visual-spatial relationships 2
• Contralateral attention (right hemisphere damage causes left-sided neglect) 2
• Prosody (emotional tone and intonation of speech) 2
• Executive functions including planning and cognitive flexibility 2

Implications for Rehabilitation

Handedness and hemispheric lateralization must be considered during both evaluation and treatment planning in neurorehabilitation 6:

• Hemispheric specializations for motor control contribute to predictable deficits depending on which hemisphere or limb is affected 6
• Performance asymmetries between dominant and nondominant hands influence rehabilitation strategies 6
• Understanding these mechanisms allows clinicians to implement targeted, evidence-based interventions to promote functional independence 6

Critical Clinical Pitfalls to Avoid

• Do not assume writing hand definitively determines cerebral dominance—this oversimplification is particularly problematic in left-handed patients where only 70% follow the typical pattern 3
• Do not proceed with dominant hemisphere surgery without formal language lateralization testing when handedness suggests atypical dominance 1
• Do not overlook handedness documentation in the neurological history, as this information is essential for risk stratification in any intervention affecting brain tissue 1

Special Populations

The incidence of atypical handedness (left-handedness and ambidexterity) is higher in epilepsy patients (13.6%) compared to the general population, though this does not correlate with specific seizure types or lesion locations 5. This elevated incidence underscores the importance of careful handedness assessment in neurological populations.