EMG changes in myasthenia gravis:
**Core Concept**
Myasthenia gravis is an autoimmune disease characterized by **fluctuating muscle weakness** due to antibodies against the **nicotinic acetylcholine receptor** at the neuromuscular junction. This leads to impaired neuromuscular transmission. Electromyography (EMG) is a diagnostic tool used to assess the electrical activity of muscles.
**Why the Correct Answer is Right**
The correct answer is related to the characteristic EMG findings in myasthenia gravis, which include a **decremental response** to repetitive nerve stimulation. This is due to the decreased number of available acetylcholine receptors, resulting in a progressive decrease in muscle action potential amplitude.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because myasthenia gravis does not typically show an incremental response.
**Option B:** Incorrect as myasthenia gravis is not associated with fasciculations.
**Option D:** Incorrect because single-fiber EMG may show jitter or blocking, not the characteristic finding of myasthenia gravis.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that myasthenia gravis patients often exhibit **worsening muscle weakness** with repeated use and **improvement with rest**.
**Correct Answer:** D. Decremental response