**Question:** All are clinical features of myasthenia gravis, except -

A. Fatigue
B. Muscle weakness
C. Muscle atrophy
D. Muscle twitching

**Core Concept:**
Myasthenia gravis (MG) is a rare autoimmune disorder that targets the neuromuscular junction, leading to a decrease in acetylcholine receptor function. This results in muscle weakness, fatigue, and easy fatigability. Muscle atrophy is not a direct consequence of MG but rather a secondary effect of prolonged weakness and disuse. Muscle twitching, on the other hand, is not a typical clinical feature of MG.

**Why the Correct Answer is Right:**
Option D ("Muscle twitching") is incorrect because twitching is typically seen in conditions like hypokalemia, hypomagnesemia, or neurogenic muscle diseases like Guillain-Barré syndrome. In MG, the clinical presentation is characterized by progressive muscle weakness and fatigue, with no prominent muscle twitching.

**Why Each Wrong Option is Incorrect:**
Option A ("Muscle atrophy") is wrong because muscle atrophy is a result of prolonged muscle disuse and immobility, which is a secondary effect of the disease rather than a primary manifestation of MG.

Option B ("Muscle twitching") is wrong as mentioned above.
Option C ("Muscle twitching") is also incorrect. Although twitching might be present in some cases, it is not a core feature of myasthenia gravis, which primarily presents with muscle weakness and fatigue.

**Clinical Pearl / High-Yield Fact:**
Myasthenia gravis is a crucial clinical entity to understand due to its potential diagnostic challenges. The disease can mimic other neuromuscular disorders, making a thorough clinical examination, including muscle strength assessment and response to neostigmine/edrophonium test, essential for diagnosis. Additionally, understanding the primary clinical features of MG helps differentiate it from other neuromuscular junction disorders and guides appropriate management and prognosis.