EMG abnomalities

Question 1

Timing between denervation and EMG abnormalities?​

Answer 1

1. Increased insertional activity 4-5 days after denervation, slightly precedes fibrillations.
2. Abnormal activity becomes prominent at 8-10 days.​
3. Fibrillations appear at 12-16 days in large animals.
4. The shorter the distance from nerve injury, the earlier the onset of fibrillation.​

Question 2

complex repetitive discharges can occasionnaly wax or wane

Answer 2

wane

Question 3

EMG findings can often be normal in which disorder?​

Answer 3

Sensory neuropathies​

Primary demyelinating neuropathies​

Acute neuropathies

Question 3

What is the maximum duration of muscle activity that can occur after cessation of electrode movement to be considered normal insertion activity?​

Answer 3

300 msec​

Question 4

State how increased insertional activity differs from abnormal spontaneous activity (fibrillations and​
positive sharp waves) in its cause and appearance.​

Answer 4

Cause ​

Increased insertional activity is caused by stimulation of abnormal myocytes by needle insertion (mechanically stimulated myofibres)​

Abnormal spontaneous activity is caused by discharge of abnormal (denervated, hypersensitive or myofibres with irritated muscle membranes) myocytes without the need for stimulation​

Appearance​

Increased insertional activity appears as a burst of electrical activity that is greatest after needle insertion and decreases/stops over time, is abrupt in onset and termination, no waxing and waning​

Abnormal spontaneous activity is persistent and independent of needle insertion​

Question 5

Electrodiagnostic changes in case of botulism​

Answer 5

• Mild to moderate decrease of CMAP amplitudes​
• Decremental response at low frequency repetitive stimulation (typically <= 3 Hz)​

*Incremental response at high frequency repetitive stimulation (typically 30 Hz)​

• dim freq endplate activity

Question 6

What is the similarities and the differences between myokymia and neuromyotonia on EMG?​

Answer 6

Both are burst of discharges of motor unit potentials (different from Fibs, PSW, CRD, and myotonia which are muscle fibre potentials) with variable frequency and amplitude (different from tremors which are rhythmic). The bursts may appear as doublets, triplets, or multiplets. Both persist during sleep and anesthesia.​

Myokymia: 5-150 Hz​

Neuromyotomia: 150-300 Hz, waning​

Question 7

What is the definition of a motor unit.​

Answer 7

Motor neuron and the myofibers it innervates​