Single fiber EMG

1. When is SFEMG used?
2. What sorts of diseases cause SFEMG to be abnormal?
3. What is fiber density? What is normal density?
4. What is jitter? What is normal?
5. What is blocking? How long does it take to resolve?

Answers:
1. If rep stim of at least three muscles is normal and abnormal diagnosis is still suspected.
2. NMJ disorders, MND, peripheral neuropathy.
3. Represents the number of single fibers belonging to the same motor unit within the recording radius of the electrode. A density of 1.5 is normal, higher represents denervation and reinnervation.
4. Small variation between the interpotential discharges of two muscle fibers of the same motor unit. Normal is 10-60 u.
5. Abnormality that occurs when a single muscle fiber AP fails to appear, which occurs with jitter > 100 u. Resolves in 1-3 months, after reinnervation is completed.