What are the key components of assessing reflexes on a neurological exam of a patient?

Reflex Assessment on Neurological Examination

The reflex examination should systematically assess deep tendon reflexes (DTRs) at the biceps, triceps, brachioradialis, patellar tendon, and Achilles tendon bilaterally, along with pathological reflexes including the Babinski sign and Hoffmann reflex, grading responses on a standardized 0-4+ scale while comparing side-to-side symmetry and upper-to-lower extremity patterns. 1, 2, 3

Core Deep Tendon Reflexes to Test

Upper Extremity Reflexes

• Biceps reflex (C5-C6): Strike the biceps tendon in the antecubital fossa while the arm is slightly flexed, observing for elbow flexion 1, 4, 5
• Triceps reflex (C7-C8): Tap the triceps tendon just above the olecranon with the arm flexed and supported, watching for elbow extension 4, 5
• Brachioradialis reflex (C5-C6): Strike the brachioradialis tendon approximately 10 cm above the wrist on the radial side, looking for forearm flexion and supination 4, 5
• Extensor digitorum reflex: This additional upper extremity reflex has demonstrated 93.65% sensitivity and 95.83% specificity for detecting upper motor neuron lesions 5

Lower Extremity Reflexes

• Patellar tendon reflex (L3-L4): Tap the patellar tendon just below the patella with the knee flexed, observing for knee extension 1, 6, 7
• Achilles tendon reflex (S1-S2): Strike the Achilles tendon with the foot dorsiflexed, watching for plantar flexion 1, 6

Pathological Reflexes

Babinski Sign

• Stroke the lateral plantar surface of the foot from heel to toe 1, 7
• Abnormal response: Extension (dorsiflexion) of the great toe with fanning of the other toes indicates upper motor neuron dysfunction 1
• This sign is a critical component of diagnostic models for conditions like degenerative cervical myelopathy 7

Hoffmann Reflex

• Flick the distal phalanx of the middle finger downward while holding the middle phalanx 7
• Abnormal response: Flexion of the thumb and index finger suggests cervical myelopathy or upper motor neuron lesion 7
• The Hoffmann reflex is a key component in diagnostic prediction models with an AUC of 0.956 for identifying cervical myelopathy 7

Grading Scale and Interpretation

Standard DTR Grading (0-4+ Scale)

• 0: Absent reflex 1, 4
• 1+: Diminished or hypoactive reflex 4
• 2+: Normal reflex 4
• 3+: Brisker than average, possibly hyperactive 4
• 4+: Hyperactive with clonus (sustained rhythmic contractions) 1, 4

Interpretation Principles

• Compare bilaterally: Side-to-side asymmetry is more significant than absolute reflex magnitude 6
• Compare upper versus lower extremities: Helps identify the level of spinal cord or nerve root pathology 6
• Assess overall pattern: Generalized hyperreflexia suggests upper motor neuron disease, while generalized hyporeflexia suggests lower motor neuron or peripheral nerve disease 1, 6

Special Examination Techniques

Jendrassik Maneuver

• When reflexes are difficult to elicit, have the patient hook their fingers together and pull apart forcefully while you test lower extremity reflexes 6
• This reinforcement technique enhances reflex responses without being pathological 6

Plantar Response Assessment

• Test the plantar reflex as part of the comprehensive examination to differentiate upper from lower motor neuron lesions 1
• An extensor plantar response (upgoing toe) is abnormal in adults and indicates corticospinal tract dysfunction 1

Context-Specific Considerations

Pediatric Examination

• Assess primitive reflexes in infants (Moro, rooting, sucking, grasp) 1
• Persistence of primitive reflexes beyond expected age suggests neuromotor dysfunction 1
• Evaluate protective reflexes and note any asymmetry 1
• The Babinski sign is normal in infants until approximately 12-24 months of age 1

Critical Care Setting

• Assess brainstem reflexes including pupillary light reflex, corneal reflex, oculocephalic reflex, oculovestibular reflex, and gag/cough reflexes 1, 8, 2
• Absent pupillary light reflex at 72 hours post-cardiac arrest has a 0-8% false positive rate for predicting poor outcomes 1, 2
• The combined absence of corneal reflex, pupillary light reflex, and motor response at 72 hours has very low false positive rates 1, 2

Diabetic Neuropathy Screening

• Test ankle reflexes as part of annual foot examination 1
• Combine with 10-g monofilament testing and at least one other sensory modality (pinprick, temperature, vibration with 128-Hz tuning fork) 1
• Absent ankle reflexes combined with abnormal monofilament testing indicates loss of protective sensation 1

Critical Pitfalls to Avoid

Technical Errors

• Inadequate hammer force: Use consistent, brisk tapping with appropriate force to elicit reflexes 4
• Wrong location: Ensure accurate tendon identification and strike location 9, 4
• Patient tension: Instruct patients to relax; muscle tension can suppress reflexes 4, 6
• Improper positioning: Position limbs correctly with appropriate joint angles 4

Interpretation Errors

• Ignoring confounding factors: Exclude sedation, paralytic agents, hypothermia (core temperature <32.5°C), severe electrolyte abnormalities, and hypoglycemia before interpreting reflexes in critical care settings 8
• Premature conclusions: In post-cardiac arrest patients, avoid prognostication before 72 hours and after excluding confounders 1, 8, 2
• Missing anatomical variants: Consider lumbosacral transitional vertebrae, nerve root malformations, or furcal nerves when clinical and imaging findings are discordant 6
• Overlooking spinal responses: Differentiate spinally mediated reflexes from retained motor responses associated with brain activity, which requires expertise 1

Documentation Requirements

• Record specific reflex grades for each tested reflex bilaterally 1, 3
• Note any asymmetry or pathological reflexes 3, 7
• Document the presence or absence of clonus 1
• Include functional observations such as the 10-second grip-and-release test when evaluating for cervical myelopathy 7

Diagnostic Integration

Cervical Myelopathy Prediction

• A diagnostic model combining sex, age, Hoffmann reflex, patellar tendon reflex, and 10-second grip-and-release test achieves an AUC of 0.956 for identifying degenerative cervical myelopathy 7
• Hyperactive patellar reflexes combined with positive Hoffmann sign strongly suggest cervical cord compression 7

Lumbar Spine Disease

• Asymmetric or absent ankle reflexes suggest S1 radiculopathy 6
• Asymmetric or absent patellar reflexes suggest L3-L4 radiculopathy 6
• Perform gait loading tests and standing extension loading tests to induce symptoms and reassess reflexes when diagnosis is unclear 6

Brain Death Evaluation

• All brainstem reflexes must be absent, including pupillary, corneal, oculocephalic, oculovestibular, and gag/cough reflexes 1
• Spinal reflexes may persist and should not be confused with brainstem function 1
• Exclude all reversible conditions before declaring brain death 1, 8