EDT EDT Clinical Correlations & Pathology 1 — Questions and Answers
Question 1: Which EDX pattern is most consistent with a diagnosis of Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy)?
- Axonal loss with active denervation on EMG
- Diffuse demyelination with prolonged distal latencies, slow conduction velocities, and absent F-waves (Correct answer)
- Length-dependent axonal polyneuropathy with distal sensory loss
- Normal NCS with myopathic EMG
Correct answer: Diffuse demyelination with prolonged distal latencies, slow conduction velocities, and absent F-waves
AIDP/GBS shows widespread demyelination including absent F-waves, prolonged distal latencies, slow conduction velocities, and conduction block.
Question 2: In diabetic polyneuropathy, the typical EDX pattern is:
- Multifocal demyelinating neuropathy sparing sensory nerves
- Length-dependent axonal sensorimotor polyneuropathy with earliest changes in distal lower extremity sensory nerves (Correct answer)
- Proximal motor neuropathy with normal sensory NCS
- Focal conduction block at common compression sites only
Correct answer: Length-dependent axonal sensorimotor polyneuropathy with earliest changes in distal lower extremity sensory nerves
Diabetic polyneuropathy is a length-dependent axonal process affecting the longest nerves first, so sural and peroneal responses are affected earliest.
Question 3: EDX findings in radial nerve palsy due to 'Saturday night palsy' (compression at the spiral groove) typically show:
- Normal motor NCS to all radial-innervated muscles
- Conduction block or axonal loss across the spiral groove sparing radial muscles proximal to the groove (Correct answer)
- Absent median and ulnar sensory responses
- Diffuse demyelinating polyneuropathy
Correct answer: Conduction block or axonal loss across the spiral groove sparing radial muscles proximal to the groove
Spiral groove compression spares proximal radial muscles (triceps, brachioradialis partially) while affecting wrist and finger extensors, with conduction block localized across the groove.
Question 4: In a patient with peroneal nerve palsy at the fibular head, needle EMG of which muscle would help differentiate it from L5 radiculopathy?
- Tibialis anterior
- Extensor hallucis longus
- Short head of the biceps femoris (Correct answer)
- Peroneus longus
Correct answer: Short head of the biceps femoris
The short head of the biceps femoris is innervated by the peroneal division of the sciatic nerve above the fibular head; denervation there indicates a more proximal sciatic or L5 lesion, not isolated fibular head palsy.
Question 5: Which EDX finding best differentiates cervical radiculopathy from brachial plexopathy?
- Reduced SNAP amplitude in the distribution of the affected root
- Abnormal needle EMG in paraspinal muscles at the affected spinal level (Correct answer)
- Prolonged F-wave latencies in the affected limb
- Reduced CMAP amplitude in the affected muscles
Correct answer: Abnormal needle EMG in paraspinal muscles at the affected spinal level
Paraspinal muscle denervation at the affected level is seen only in radiculopathy because the posterior primary ramus arises proximal to the plexus.
Question 6: EDX evaluation of multifocal motor neuropathy (MMN) characteristically reveals:
- Symmetric axonal polyneuropathy with sensory predominance
- Multiple sites of persistent motor conduction block without sensory abnormalities (Correct answer)
- Diffuse demyelination with sensory involvement
- Normal NCS with myopathic EMG
Correct answer: Multiple sites of persistent motor conduction block without sensory abnormalities
MMN is characterized by multiple sites of persistent motor conduction block (>50% amplitude drop) with normal sensory NCS, distinguishing it from CIDP.
EDT EDT Clinical Correlations & Pathology 1
Which EDX pattern is most consistent with a diagnosis of Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy)?