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Electromyogram
Aka: Electromyogram, Electromyography, EMG
- Indications
- Muscle disease
- Neuromuscular junction disease
- Nerve or nerve root disease with denervation
- Background
- Electrical test to measure muscle physiology
-
Myopathy Findings
- Nonspecific for Myopathy type
- Motor unit potential abnormalities
- Low amplitude
- Short duration
- Complex, polyphasic
- Increased Insertional activity
- Ectopic high frequency discharges
- Fibrillation potentials present in some myopathies
- Polymyositis
- Muscular Dystrophy
- Myotonia findings
- Waxing and waning hyperexcitability
- Repetitive discharges
- Electromyogram machine creates "dive bomber" sound
- Neuromuscular junction disorder findings
- General
- Increased variation in muscle response time (latency)
- Presynaptic disorders
- Examples
- Botulism
- Eaton -Lambert Syndrome
- Findings
- Enhanced response to repetitive nerve stimulation
- Normal amplitude miniature end-plate potentials
- Postsynaptic disorders
- Examples
- Myasthenia Gravis
- Findings
- Decreased response to repetitive nerve stimulation
- Subnormal amplitude miniature end-plate potentials
- Denervation Findings
- Increased polyphasic action potentials
- Ectopic high frequency discharges
- Fibrillations
- Onset 3 to 4 weeks after nerve injury
- Fasciculations
- Positive sharp waves
- F Response prolonged (proximal Motor Nerve reflex arc)
- Guillain-Barre Syndrome
- Hoffman Reflex (Stretch reflex arc - sensory and motor)
- Sensory Nerve root lesion
- Motor Nerve root lesion