Reflex Techniques for Nervous System Evaluation
Reflex testing is a fundamental neurological examination technique that assesses the functional integrity of specific nerve pathways, nerve roots, and central nervous system structures through standardized elicitation of involuntary motor responses to sensory stimuli. 1, 2
Core Principles of Reflex Testing
Reflexes provide immediate information about both motor and sensory pathways without requiring patient cooperation, making them invaluable for localizing neurological lesions 2. The examination evaluates afferent sensory pathways, central processing in the spinal cord or brainstem, and efferent motor pathways in a single integrated assessment 1, 3.
Standard Grading System
All deep tendon reflexes are graded on a uniform 0-4+ scale 4:
- 0: Absent reflex (no response)
- 1+: Diminished/hypoactive (trace response, less than normal)
- 2+: Normal response
- 3+: Brisker than average (possibly but not necessarily pathologic)
- 4+: Hyperactive with clonus (definitively abnormal)
Asymmetry between sides is often more clinically significant than the absolute grade, as focal pathology can manifest even when both sides fall within the "normal" range 4.
Deep Tendon Reflex Techniques
Upper Extremity Reflexes
Triceps reflex (C7-C8, radial nerve): Position the patient's arm flexed at 90 degrees at the elbow with support. Strike the triceps tendon directly above the olecranon process and observe for elbow extension 4. This reflex is particularly valuable for localizing cervical radiculopathy at the C7-C8 levels 4.
Biceps and brachioradialis reflexes: These follow similar positioning principles with the arm supported and relaxed, striking the appropriate tendon with a reflex hammer 5.
Key Technical Considerations
The force applied with the reflex hammer significantly affects the response quality 5. The hammer should deliver consistent, brisk taps rather than forceful strikes. Proper execution technique is critical—improper assessment methods can alter findings and obscure the true state of the nervous system 5.
Always test both sides for comparison, as unilateral changes provide crucial localizing information 4.
Brainstem Reflex Techniques
Brainstem reflexes offer immediate information about cranial nerve functionality and overall brainstem integrity 2, 3.
Corneal Reflex
Touch the cornea with a wisp of tissue paper, cotton swab, or squirts of water while observing for eyelid movement 1. No eyelid movement indicates an absent reflex. This tests the trigeminal nerve (afferent) and facial nerve (efferent) pathways through the pons 1, 3.
Pupillary Light Reflex
Document pupillary response to bright light in both eyes 1. Pupils are typically 4-9 mm and should constrict briskly to light. Use a magnifying glass when uncertainty exists about the response 1. Absent responses with midposition or fully dilated pupils indicate brainstem dysfunction 1.
Oculovestibular Reflex (Caloric Testing)
After confirming external auditory canal patency, elevate the head to 30 degrees 1. Irrigate each ear separately with 10-50 mL of ice water, waiting several minutes between sides 1. Observe for eye movement during 1 minute of observation—absence of movement indicates brainstem dysfunction 1.
Gag and Cough Reflexes
Test the pharyngeal reflex by stimulating the posterior pharynx with a tongue blade or suction device 1. For the tracheal reflex, insert a suction catheter to the level of the carina and perform 1-2 suctioning passes while observing for cough 1. These assess the glossopharyngeal and vagus nerves 1.
Spinal Reflex Techniques
Spinal reflexes provide crucial information about spinal cord and peripheral nerve functionality 2.
H-Reflex Testing
The H-reflex of the soleus muscle and other spinal reflexes can be monitored continuously during surgical procedures without inducing movement in the surgical field 2. These reflexes provide both motor and sensory information on the functional integrity of nerve fibers and nuclei 2.
Clinical Interpretation Patterns
Lower Motor Neuron Dysfunction (Diminished/Absent Reflexes)
Reflexes graded 0-1+ suggest 4:
- Peripheral neuropathy
- Nerve root compression
- Anterior horn cell disease
- Neuromuscular junction disorders
- Myopathies
Upper Motor Neuron Dysfunction (Hyperactive Reflexes)
Reflexes graded 3-4+ indicate 4:
- Corticospinal tract lesions
- Spinal cord pathology
- Cerebral lesions affecting motor pathways
Bilateral upper limb hyperreflexia most commonly indicates cervical myelopathy, particularly in patients with congenital or degenerative spinal canal stenosis 6. Look for accompanying upper motor neuron signs including spasticity, clonus, positive Babinski sign, and upper motor neuron pattern weakness 6.
Specialized Reflex Testing Applications
Electrophysiological Reflex Monitoring
Compound muscle action potentials (CMAPs) can be elicited by supramaximal nerve stimulation, providing higher signal-to-noise ratios than spontaneous EMG 1. Stimulus intensity should be set 20-50% above that required for maximal response to ensure supramaximal activation 1.
Phrenic nerve/diaphragm latencies average 6-8 milliseconds in adults when elicited by electrical stimulation at the neck, with the right side slightly shorter due to the shorter nerve length 1. CMAP amplitudes recorded from chest wall surface electrodes average 500-800 μV 1.
Intraoperative Monitoring
Reflex monitoring provides continuous feedback during surgical procedures without disrupting the surgical field 2. Brainstem reflexes (blink reflex, laryngeal adductor reflex) and spinal reflexes can be monitored in real-time to detect potential neurological damage 2, 3.
Critical Pitfalls to Avoid
Never conclude that reflexes are abnormal based on a single examination—factors including patient anxiety, medications, and cooperation level significantly affect responses 4. Document these factors to aid interpretation 4.
Do not rely solely on reflex testing for diagnosis—reflexes must be interpreted within the complete clinical context including history, other examination findings, and appropriate imaging 6.
Avoid testing reflexes without proper patient positioning and relaxation—muscle tension and improper positioning produce unreliable results 5.
When using electrophysiological techniques, regularly verify that stimulus intensity remains supramaximal during long experiments 1. Failure to maintain adequate stimulation intensity produces falsely diminished responses 1.