EMG/NCS Basics Flashcards
What is the main feature of axonopathy on NCS?
Decreased amplitude (CMAP / SNAP)
Note - may have mild reduction in conduction velocity due to loss of large myelinated nerve fibres
What is the main feature of demyelination on NCS?
Slowing / reduced conduction velocity
Also:
- Dispersion
- Prolonged distant latencies
- Slowing of F latencies
- Conduction block
What are the main features of axonopathy on EMG?
Distal neurogenic pattern:
- High amplitude, polyphasic motor units
- Fibrillations / positive sharp waves
What are the main features of demyelination on EMG?
Reduced motor unit recruitment
What are the main differentials of demyelination on NCS?
AIDP
CIDP
HSMN1 (Charcot-Marie Tooth)
Multifocal motor neuropathy
What are the main differences on NCS between HSMN1 and MMN?
HSMN1 = no conduction block or dispersion MMN = conduction block
What is the diagnostic feature of LEMS on NCS?
Post-tetanic CMAP increase by >50%
What does the finding of jitter suggest on single fibre EMG?
Neuromuscular junction blockade - both MG and LEMS
What is the diagnostic feature of myasthenia gravis on NCS?
Decrement on repetitive stimulation
What are the EMG findings in MG and LEMS?
Jitter on single fibre EMG, but otherwise normal study
What does increased insertional activity on EMG indicate?
Denervation (neurogenic pattern)
What does increased spontaneous activity on EMG indicate?
Denervation (neurogenic pattern)
What does giant polyphasic units indicate?
Reinervation
What are the findings on EMG in myopathy?
May see spontaneous activity
Reduced duration
Reduced amplitude
Polyphasia
Early recruitment
Polyphasia may be seen on EMG in which conditions?
Chronic denervation
Myopathy
