From the Research
The typical amplitude of facilitations on electromyography (EMG) ranges from 100% to 400% increase compared to baseline compound muscle action potential (CMAP) amplitude. Facilitation is most commonly assessed during repetitive nerve stimulation (RNS) testing, where a brief exercise or 10-second maximal voluntary contraction is performed before stimulating the nerve again. In normal individuals, facilitation typically produces a modest increase in CMAP amplitude of less than 50%. However, in conditions like Lambert-Eaton myasthenic syndrome (LEMS), facilitation is markedly increased, often exceeding 200% and sometimes reaching 400% or more of the baseline amplitude. This dramatic increase occurs because exercise temporarily overcomes the calcium channel dysfunction at the neuromuscular junction that characterizes LEMS, allowing more acetylcholine release and thus greater muscle fiber recruitment. The degree of facilitation can help differentiate LEMS from myasthenia gravis, where facilitation is typically minimal or absent. The amplitude increase is temporary and will gradually return to baseline within minutes after the facilitating exercise.
Some key points to consider:
- The provided evidence does not directly address the question of typical amplitude of facilitations on EMG, but it does provide information on the treatment and management of myasthenia gravis and Lambert-Eaton myasthenic syndrome, which can be related to EMG findings 1, 2, 3, 4, 5.
- The most recent and highest quality study is from 2022, which discusses the effectiveness and side effects of pyridostigmine in the treatment of myasthenia gravis, but does not provide specific information on EMG facilitation amplitudes 5.
- Based on general knowledge of EMG and neuromuscular disorders, the typical amplitude of facilitations on EMG can range from 100% to 400% increase compared to baseline CMAP amplitude, with significant variations depending on the underlying condition and individual patient characteristics.