Myasthenia gravis (MG) is best described as which condition?

• A. A genetic muscular dystrophy.
• B. A peripheral nerve demyelinating disease.
• C. An autoimmune disorder where antibodies block acetylcholine receptors at the neuromuscular junction, causing fluctuating skeletal muscle weakness.
• D. A spinal muscular atrophy.

Answer: (C)

Myasthenia gravis is an autoimmune disorder in which antibodies attack acetylcholine receptors at the neuromuscular junction. This reduces the number of functional receptors and disrupts transmission from nerve to muscle, leading to fatigable weakness that worsens with activity and improves with rest. The weakness often starts with eye muscles (ptosis, diplopia) and can involve bulbar and limb muscles. This mechanism distinguishes MG from genetic muscular dystrophies (which involve structural muscle defects), peripheral nerve demyelinating diseases (which affect nerve conduction), and spinal muscular atrophy (neurogenic muscle weakness from motor neuron loss).