From the Research
The typical amplitude of fasciculations on EMG is around 0.39 ± 0.25 mV in patients with EMG-detected fasciculations alone, and 1.22 ± 0.92 mV in those with both EMG-detected and ultrasound-detected fasciculations 1. Fasciculations appear as spontaneous, irregular discharges of a motor unit that occur randomly and unpredictably during EMG recording. These brief electrical potentials usually last between 0.5 to 10 milliseconds and have a characteristic irregular firing pattern. The amplitude can vary depending on the underlying cause, with higher amplitudes often seen in more severe neurogenic conditions like amyotrophic lateral sclerosis (ALS). When interpreting fasciculations on EMG, it's essential to consider not just their amplitude but also their morphology, stability, and distribution across multiple muscles, as these characteristics help differentiate benign fasciculations from those associated with pathological conditions. Some key points to consider when evaluating fasciculations on EMG include:
- The presence of other abnormal spontaneous activities like fibrillation potentials or positive sharp waves alongside fasciculations often indicates more significant lower motor neuron pathology.
- The use of high-density surface electromyography (HDSEMG) and the Surface Potential Quantification Engine (SPiQE) can improve the detection and analysis of fasciculations 2.
- Benign fasciculation syndrome (BFS) has a favorable prognosis, regardless of minor EMG abnormalities, and does not necessarily imply progression to ALS 3.
- A thorough understanding of the symptomatology, potential cause(s), progression, and treatment of ALS is essential to provide timely and high-quality patient care, and electrodiagnostic examination, specifically electromyography (EMG) and nerve conduction studies (NCS), is one of the key diagnostics of ALS 4. It is also worth noting that MR neurography can be an accurate method for assisting in the differential diagnosis of amyotrophic lateral sclerosis and multifocal motor neuropathy 5.