How do I properly assess deep‑tendon reflexes and interpret abnormal findings?

Deep Tendon Reflex Assessment and Interpretation

Assess deep tendon reflexes systematically using standardized technique with a reflex hammer, applying 21-50 Newtons of force for normal reflexes, and interpret abnormalities based on whether they indicate upper motor neuron (hyperreflexia) or lower motor neuron (hyporeflexia/areflexia) pathology. 1, 2

Proper Assessment Technique

Equipment and Force Application

• Use a reflex hammer (Babinski, Queen Square, or Taylor) with appropriate force ranges: 0-20 Newtons for hyperreflexia testing, 21-50 Newtons for normal reflexes, and >50 Newtons when hyporeflexia is suspected 2
• The Taylor hammer has limitations in the hyporeflexic range due to its small mass and short handle, creating a ceiling effect 2

Lower Extremity Reflexes

Patellar Reflex (L2-L4):

• Begin with standard technique with patient seated, legs dangling 3
• If reflexes are difficult to elicit (especially in elderly patients with paratonia), use the "superior patellar supine" method as your second-line approach—this was the best single alternative method in 42% of difficult cases 3
• The patellar reflex is typically preserved longer than ankle reflexes in length-dependent neuropathies 1

Achilles Reflex (S1):

• Start with the "plantar strike method" (striking the plantar surface while dorsiflexing the foot) rather than standard Achilles tendon tapping 3
• If unsuccessful, proceed to the "Achilles strike elevated" method with the foot elevated 3
• These alternative methods reduced error rates from 84% to 21% in elderly patients where reflexes were incorrectly called absent using standard techniques alone 3
• The Achilles reflex is affected earlier and more severely in length-dependent peripheral neuropathies like diabetic neuropathy 1

Upper Extremity Reflexes

Biceps/Brachioradialis Reflex:

• Test with forearm in midway position (90 degrees) initially 4
• Be aware that the brachioradialis reflex can be elicited by both stretch and phasic vibration, and response depends critically on forearm position 4
• In 94% of normal patients, radial tap-induced biceps contraction disappears when the forearm is supinated 4

Enhancement Maneuvers

• Use the Jendrassik maneuver (patient hooks fingers together and pulls) when reflexes are difficult to elicit 5, 6
• This technique enhances reflex responses without changing the underlying pathology 5

Interpretation of Abnormal Findings

Hyperreflexia (Increased Reflexes)

Upper Motor Neuron Pathology:

• Hyperreflexia with spasticity, positive Babinski sign, and weakness indicates pyramidal tract lesions 7
• Look for associated findings: increased tone, clonus, and extensor plantar responses 7, 8
• In stroke patients with hyperreflexia, the biceps contraction persists in supination after radial tap in 84% of cases—a finding absent in normal individuals 4

Hyporeflexia/Areflexia (Diminished or Absent Reflexes)

Lower Motor Neuron Pathology:

• Diminished reflexes indicate pathology anywhere along the reflex arc: peripheral nerve, nerve root, or anterior horn cell 1
• Critical diagnostic pattern: Assess which specific reflex is affected to localize the lesion:
  • Absent patellar reflex only → L2-L4 radiculopathy 1
  • Absent Achilles reflex only → L5-S1 radiculopathy or S1 nerve root lesion 1
  • Both reflexes absent → consider plexopathy (L1-S3 for lumbosacral) or generalized peripheral neuropathy 1

Specific Clinical Contexts:

Diabetic Neuropathy:

• Loss of Achilles reflex correlates with inability to detect 5.07 (10g) monofilament, indicating loss of protective sensation 1
• Diabetic amyotrophy presents with proximal weakness, wasting, and diminished reflexes in lower limbs 1
• Always check vibratory sense and position sense alongside reflexes 1

Radiculopathy:

• When clinical and imaging findings are discrepant, consider lumbosacral transitional vertebrae, nerve root malformations, or furcal nerve variants 5
• Needle EMG has 90% sensitivity for lumbosacral radiculopathy; nerve conduction studies alone have low diagnostic value 1
• Assess reflexes after gait loading test or standing extension loading test to unmask latent radiculopathy 5

Medication-Induced Neuropathy:

• Bortezomib causes suppression of deep tendon reflexes proportional to sensory loss 1
• Thalidomide causes bilateral symmetric sensory disorders with diminished reflexes in 70% of patients treated for 12 months 1

Metabolic Causes:

• Vitamin B6 deficiency progresses from paresthesias to loss of distal sensation, motor ataxia, and loss of deep tendon reflexes 1
• In hepatic encephalopathy, reflexes may diminish or disappear in noncomatose patients, though pyramidal signs can still be present 1

Critical Assessment Principles

Determining Pathological Changes

• Compare side-to-side differences (asymmetry suggests focal pathology) 5
• Compare upper versus lower extremities (helps distinguish generalized from focal processes) 5
• Assess overall balance across all limbs to determine if changes are pathological 5

Common Pitfalls to Avoid

• In elderly patients: Standard techniques miss reflexes in 37% of knee jerks and 84% of ankle jerks—always use alternative methods when standard approach fails 3
• Examiner factors: Inconsistent hammer force, improper patient positioning, and inadequate muscle relaxation reduce objectivity 5, 6
• Patient factors: Paratonia, frontal rigidity, anxiety, and inability to relax alter reflex responses 3
• Post-ictal state: An extensor plantar response immediately after seizure is expected and does not indicate structural pathology unless it persists beyond 5-10 minutes 8

When to Pursue Further Workup

• Persistent asymmetric reflex changes warrant electrodiagnostic studies to differentiate radiculopathy from plexopathy 1
• Diminished reflexes with sensory loss require monofilament testing and assessment of vibratory/position sense 1
• In infants <18 months with post-ictal drowsiness and extensor plantar response, perform lumbar puncture to exclude meningitis 8