What is a key finding in electromyography (EMG) for Myasthenia Gravis (MG)?

In Myasthenia Gravis (MG), the key finding in electromyography (EMG) is a decremental response to repetitive nerve stimulation. This phenomenon occurs because MG is an autoimmune disorder affecting the neuromuscular junction, where antibodies are produced against acetylcholine receptors. As repetitive nerve stimulation occurs, there is a progressive decrease in the muscle's ability to respond due to the depletion of available acetylcholine receptors that are effectively functioning. The first few stimuli may show a normal response, but with continued stimulation, the muscle action potential decreases, reflecting fatigue and weakness, which is characteristic of MG.

This decremental response highlights the impaired synaptic transmission at the neuromuscular junction, which is central to the pathophysiology of MG. The other options suggest alternative responses that do not accurately represent the EMG findings seen in this condition. Incremental responses, stable responses, or pathological responses are more indicative of different neuromuscular disorders or normal conditions, making the decremental response a hallmark feature specific to Myasthenia Gravis.