What are some of the most obscure neurophysical exam findings?

Obscure Neurological Physical Examination Findings

The critical flicker frequency test, palmomental reflex, and HINTS examination are among the most obscure yet clinically valuable neurological examination findings that can significantly impact diagnosis and management of neurological conditions. 1, 2

Primitive Reflexes

Palmomental Reflex

• Elicited by firmly stroking the thenar eminence of the palm with a blunt object
• Positive response: contraction of the ipsilateral mentalis muscle (chin muscle)
• Clinical significance:
  • Present in 70% of normal subjects but often undetectable by visual inspection 3
  • More frequent in Alzheimer's patients under 80 years (25% vs 7% in controls) two years before diagnosis 4
  • Indicates frontal lobe dysfunction when pronounced

Grasp Reflex

• Elicited by stroking the patient's palm from proximal to distal
• Positive response: involuntary grasping movement
• Indicates frontal lobe pathology when present in adults 1

Snout Reflex

• Elicited by tapping the closed lips in the midline
• Positive response: puckering or pouting of the lips
• Associated with diffuse cerebral dysfunction 1

Advanced Oculomotor Testing

HINTS Examination

• Head Impulse, Nystagmus, Test of Skew
• More sensitive than early MRI for detecting stroke in acute vestibular syndrome 2
• Components:
  • Head impulse test: rapid head rotation while patient fixates on examiner's nose
  • Nystagmus evaluation: direction-changing vs direction-fixed
  • Test of skew: vertical ocular misalignment

Optokinetic Nystagmus Testing

• Absence of normal optokinetic nystagmus vertically is an early sign of progressive supranuclear palsy 1
• More sensitive than obvious vertical gaze palsy which appears later

Saccadic Eye Movement Velocity

• Decreased velocity of saccades, particularly downward, can indicate progressive supranuclear palsy before full gaze palsy develops 1

Specialized Neurophysiological Tests

Critical Flicker Frequency Test

• Assesses the degree of vigilance by measuring the threshold at which a flickering light appears continuous
• Particularly useful in quantifying low-grade hepatic encephalopathy 1
• Advantages:
  • Objective assessment
  • Not affected by learning effects in repeated testing
  • Correlates with severity of encephalopathy

Hoffmann Reflex

• Electrical analog of the stretch reflex
• Elicited by electrical stimulation of the median nerve at the wrist
• Measures monosynaptic reflex arc integrity
• Useful for detecting subtle upper motor neuron lesions 5

Advanced Motor Testing

Alien Hand Phenomenon Assessment

• Test for autonomous, seemingly purposeful movements of a limb that the patient denies controlling
• Suggests corticobasal syndrome when present 1

Stimulus-Sensitive Myoclonus

• Elicited by unexpected tactile, auditory, or visual stimuli
• Indicates cortical hyperexcitability
• Associated with corticobasal syndrome and other neurodegenerative conditions 1

Pitfalls and Considerations

• Primitive reflexes may be present in normal elderly individuals but are typically more pronounced and consistent in pathological states
• Neurophysiological tests like critical flicker frequency require specialized equipment but may detect abnormalities when standard neurological examination is normal 1
• Interpretation of these obscure signs should be done in context with other clinical findings
• Serial examinations often provide more valuable information than single assessments 2

Clinical Application Algorithm

1. For suspected neurodegenerative disorders:

   • Assess primitive reflexes (palmomental, grasp, snout)
   • Evaluate for subtle parkinsonian signs (asymmetric rigidity)
   • Test saccadic eye movements for velocity changes

2. For acute vestibular symptoms:

   • Perform HINTS examination before ordering neuroimaging
   • More sensitive than early MRI for stroke detection

3. For suspected hepatic encephalopathy:

   • Consider critical flicker frequency testing when standard tests are inconclusive
   • Particularly valuable in patients with multiple comorbidities or low educational background

4. For subtle upper motor neuron lesions:

   • Evaluate Hoffmann reflex when clinical signs are equivocal
   • Compare side-to-side differences for asymmetry

These obscure neurological examination findings, when properly elicited and interpreted, can provide valuable diagnostic information that may not be evident on standard neurological examination or even advanced neuroimaging.