Neuromuscular disorders, peripheral neuropathy, and electromyography
Neuromuscular disorders, peripheral neuropathy, and electromyography
The exam tests anatomic localization, nerve conduction study patterns, needle EMG interpretation, and emergency neuromuscular care. Distinguish demyelinating from axonal neuropathy: demyelination shows slowed conduction, prolonged distal latency, conduction block, or temporal dispersion; axonal loss shows reduced amplitudes. Guillain-Barre syndrome causes ascending areflexic weakness with albuminocytologic dissociation and demyelinating NCS; treat with IVIG or plasma exchange, not steroids, and monitor vital capacity. Myasthenia gravis shows fatigable weakness, decrement on repetitive stimulation, and improvement with ice or edrophonium; crisis requires respiratory monitoring. ALS shows widespread active denervation and reinnervation without sensory loss.
Worked example
A 35-year-old develops ascending leg weakness and areflexia after diarrhea. CSF shows elevated protein without cells; NCS shows demyelinating features. Reasoning: GBS. Admit, monitor forced vital capacity, and give IVIG or plasma exchange. Steroids alone are not indicated.
Traps
Do not rely on early EMG to exclude a neuromuscular disorder; do not give steroids for GBS; do not miss respiratory failure in myasthenic crisis; do not interpret mild sensory symptoms as ALS; distinguish CIDP from GBS by time course and treatment response.