Which statement best describes the pathophysiology and hallmark exam finding of myasthenia gravis?

• A. Autoimmune antibodies against acetylcholine receptors (or MuSK) causing fatigable weakness with ptosis and diplopia
• B. Demyelination of central neurons causing spasticity
• C. Hyperactive reflexes with sustained clonus
• D. Sensory loss is predominant

Answer: (A)

Autoimmune disruption at the neuromuscular junction reduces the effectiveness of acetylcholine signaling. In myasthenia gravis, antibodies target postsynaptic acetylcholine receptors (AChR) or MuSK, which leads to fewer functional receptors and a diminished safety factor for neuromuscular transmission. Because the system has limited reserve, strength wans with use (fatigable weakness), and ocular muscles are frequently affected, producing ptosis and diplopia. Clinically, this fatigable pattern with eye involvement is the hallmark you’d expect to see on exam, often improving with rest or after giving anticholinesterase medications.

Other choices describe different disorders: demyelination of central neurons causes spasticity and is not typified by fatigable, ocular-predominant weakness; hyperactive reflexes with sustained clonus suggest upper motor neuron pathology; sensory loss predominance points toward peripheral neuropathies or dorsal column disease.