Hello. This teachable moment will address the question, do fibrillation potentials always fire in a regular firing pattern? Fibrillation potentials are common waveforms that are recorded during needle EMG. They are the most common abnormal spontaneous waveform and they occur due to the action potential of individual muscle fibers that are firing in the absence of innervation. So they are derived from a denervated muscle fiber. The way that a fibrillation potential is identified is based on its firing pattern. And typically, fibrillation potentials fire in what we term a regular firing pattern. What that means is that when the fibrillation potential or the spike is recurring and firing repeatedly, the inter-spike interval for each time it fires has a definable change. And usually that change is a gradual increase in the inter-spike interval or a gradual slowing of the fibrillation potentials. And many times the fibrillation potential will gradually slow to finally stopping if the needle is not moved any further. Sometimes fibrillation potentials have a completely fixed inter-spike interval and they continue on and fire continuously for a prolonged period of time. So what defines a fibrillation potential in the vast majority of situations is the fact that a potential fires in this regular firing pattern. And it looks and sounds something like this. However, there are rare instances where a fibrillation potential can fire in an irregular firing pattern. The times that this occurs, at least anecdotally and in my experience, are when there's early denervation, so usually within a few days or a few weeks after an acute denervating process. And in that situation, as fibrillation potentials are being developed and starting to form, the fibrillation potentials may fire in an irregular firing pattern. And they may have features that would be more typical of in-plate spike firing patterns. However, they're truly fibrillation potentials as the needle is moved in different areas. Fibrillation potentials may be seen in multiple areas, and that's different than in-plate in which when one moves the needle away from the in-plate, the baseline should be quiet. Now I would caution you to be careful about over-interpreting irregular firing spikes. In most cases, those are going to be in-plate spikes. But in the right clinical context and when it's seen in multiple areas of the muscle, in early denervating processes, fibrillation potentials may fire irregularly. I feel much more confident when I also see regular firing fibrillation potentials mixed in with the irregular fibs to consider and call those irregular spikes as fibrillation potentials. So the answer to the question is that yes, fibrillation potentials in very rare instances in early denervation can fire in an irregular firing pattern.

fibrillation potentials

needle EMG

abnormal waveforms

denervated muscle fibers

irregular firing patterns