BandersnatchF
Well-known member
What your neuro meant is that "a clean/normal EMG in an area that has fasciculations (even if they're not present during the EMG) rules out ALS as a cause for the fasciculations."
An EMG will only pick up signs of lower motor neuron (LMN) problems. Upper motor neuron (UMN) death won't necessarily cause changes in an EMG. Symptoms of UMN problems include weakness, hyperreflexia, and spasticity, but not fasciculations. In other words, there can be weakness if UMNs are dying, but nothing may show on the EMG. There won't be fasciculations either. LMN symptoms include weakness, hyporeflexia, and fasciulations. Side effects of dying LMNs will show up on an EMG.
The thing is that weakness in ALS can come from either LMN or UMN death (or both). If there's weakness but no fasciculations, it's possible that UMNs are dying but the LMNs aren't (yet), and the EMG might be normal. If there are fasciculations (and you wouldn't be here if you didn't have them
), the EMG would pick up abnormalities if they were due to LMN death or many other disorders including a pinched nerve and BFS.
This can be one of the problems in diagnosing ALS - weakness alone may not cause an abnormal EMG initially. However, fasciculations will result in an abnormal EMG if they're due to LMN death because the fasciculations are a side effect of the muscles dying due to LMN disconnection. The EMG can be abnormal even in the absence of LMN problems (as many here can attest to), but a clean EMG indicates that problems with the LMNs are not the cause of the fasciculations.
I should add that some BFS twitches aren't true fasciculations (especially true for twitches outside the legs), and might not show up on an EMG.
An EMG will only pick up signs of lower motor neuron (LMN) problems. Upper motor neuron (UMN) death won't necessarily cause changes in an EMG. Symptoms of UMN problems include weakness, hyperreflexia, and spasticity, but not fasciculations. In other words, there can be weakness if UMNs are dying, but nothing may show on the EMG. There won't be fasciculations either. LMN symptoms include weakness, hyporeflexia, and fasciulations. Side effects of dying LMNs will show up on an EMG.
The thing is that weakness in ALS can come from either LMN or UMN death (or both). If there's weakness but no fasciculations, it's possible that UMNs are dying but the LMNs aren't (yet), and the EMG might be normal. If there are fasciculations (and you wouldn't be here if you didn't have them
), the EMG would pick up abnormalities if they were due to LMN death or many other disorders including a pinched nerve and BFS.This can be one of the problems in diagnosing ALS - weakness alone may not cause an abnormal EMG initially. However, fasciculations will result in an abnormal EMG if they're due to LMN death because the fasciculations are a side effect of the muscles dying due to LMN disconnection. The EMG can be abnormal even in the absence of LMN problems (as many here can attest to), but a clean EMG indicates that problems with the LMNs are not the cause of the fasciculations.
I should add that some BFS twitches aren't true fasciculations (especially true for twitches outside the legs), and might not show up on an EMG.