SFEMG FAQs

These are some frequent questions we have received over the years.
Take a look and see if you know the answers, or learn something new.... /Erik & Don

Axon Reflex

- During SFEMG with stimulation I sometimes see one spike occurring with two distinct latencies, particularly when I increase and decrease the stimulation strength when testing for threshold stimulation. What is this?   Show/Hide Answer

- What is axon reflex?   Show/Hide Answer

- What is axon reflex, cont'd ?   Show/Hide Answer

Botox

- Does Botox interfere with SFEMG interpretation?   Show/Hide Answer

- For how long time do we see the effect of Botox?   Show/Hide Answer

Fiber Density

- Can we assess FD with CNE?   Show/Hide Answer

LEM

- How to distinguish between a pre and post synaptic defect with SFEMG?   Show/Hide Answer

MG

- SFEMG is unspecific for MG, comment   Show/Hide Answer

- How many muscles should be studied in a routine work up for MG?   Show/Hide Answer

- Do we need NCS and EMG when we have abnormal SFEMG in case of MG?   Show/Hide Answer

- Do we need to stop medications before SFEMG in MG?   Show/Hide Answer

- Which muscle is more often abnormal, Frontalis or ED in MG?   Show/Hide Answer

- Do you use SFEMG for follow up studies in MG?   Show/Hide Answer

- Are there no false positives in the diagnosis of Myasthenia Gravis with SFEMG?   Show/Hide Answer

- Which measure of jitter best correlates or predicts change in MG disease severity?   Show/Hide Answer

- How does change in jitter correlate with change in measures of MG disease severity?   Show/Hide Answer

MNE

- Are there any references to the use of monopolar needle electrodes for jitter measurements despite the increased recording area?   Show/Hide Answer

Pathology

- How can we tell if increased jitter is due to reinnervation or MG?   Show/Hide Answer

RNS and SFEMG

- What is the relationship between RNS and jitter?   Show/Hide Answer

- Can we have abnormal RNS and normal SFEMG?   Show/Hide Answer

- I have tried stimulation SFEMG, 3Hz but I cannot see any decrementing response, even in a case of clear myasthenia. Why?   Show/Hide Answer

Routine

- Practitioners are advised to record 100 discharges per recording. In cases where there is patient movement or artefact, can the recordings be further filtered? What is the minimal acceptable amount of discharges per recording in such case?   Show/Hide Answer

- If jitter is abnormal for spikes 2 and 3 in a triplet, shall we count 1 or 2 values?   Show/Hide Answer

- Do we always need 20 jitter values in routine cases?   Show/Hide Answer

- Which drugs may inflence jitter values?   Show/Hide Answer

- Electrode position. Do you prefer close to or remote from end-plate zone?   Show/Hide Answer

- What is the minimum number of individual jitter values we need to measure?   Show/Hide Answer

- In a patient with ptosis and normal SFEMG, what is the interpretation?   Show/Hide Answer

- Is 10% abnormal jitter values the accepted upper limit?   Show/Hide Answer

- Should we rotate the CNE electrode for optimal recording?   Show/Hide Answer

- SFEMG in small children?   Show/Hide Answer

- Can we have blocking with normal jitter?   Show/Hide Answer

- In two different sites, we may record from fibers of the same MU. Problem?   Show/Hide Answer

- Do we need temperature control for jitter studies?   Show/Hide Answer

- Are there reference limits for jitter in babies?   Show/Hide Answer

- Do you measure amplitude of SFEMG action potentials?   Show/Hide Answer

- Is there an upper latency limit for a signal to be accepted in stimulation SFEMG?   Show/Hide Answer

- Why is there an upper limit of IPI for voluntary jitter signals?   Show/Hide Answer

- To assess pathology, is the mean MCD value or number or outliers best?   Show/Hide Answer

- How can we interpret a jitter values < 5 usec?   Show/Hide Answer

- Can moderately or severely disturbed neuromuscular transmission (as in myasthenia gravis) be seen by means of conventional EMG?   Show/Hide Answer

- Can we make jitter studis in neck extensors, e.g. in Musk MG?   Show/Hide Answer

Stimulated SFEMG

- In stimulated SFEMG, what stimulus duration is recommended?   Show/Hide Answer

- Surface or needle stim for Stim SFEMG?   Show/Hide Answer

- Why do we need more jitter values for stimulation than volitional jitter studies?   Show/Hide Answer

Technique

- Can you use some mechanical device to keep the electrode in an optimal position?   Show/Hide Answer

- Which of MCD and MSD should we report as the "jitter" value?   Show/Hide Answer

- Which is the difference between volitional and stimulation SFEMG?   Show/Hide Answer

- Why not high pass filter of 2KHz instead of 1KHz for CNE jitter measurement?   Show/Hide Answer

- What low pass filter (high filter) do you recommend for CNE jitter recording?   Show/Hide Answer

- What is the difference between amplitude level and peak time measurements of jitter?   Show/Hide Answer

- Why do you recommend to truncate values > 150 usec?   Show/Hide Answer

- Why calculate the MSD?   Show/Hide Answer

- What is JSUM?   Show/Hide Answer

- Can we buy proper SFEMG electrodes?   Show/Hide Answer

- What is jiggle and how is it related to jitter?   Show/Hide Answer

- How do you use the IPI/IDI plot?   Show/Hide Answer

- How is jitter affected in myopathy?   Show/Hide Answer

- SFEMG, voluntary activation. I sometimes see highly increased jitter (150 ┬Ásec), but no blocking is observed. Why? - see above   Show/Hide Answer