How do myasthenia gravis and Lambert-Eaton syndrome differ in their typical patterns of weakness and response to activity?

• A. MG has fatigable weakness that worsens with use and often ptosis/ophthalmoplegia; LEMS shows proximal weakness with autonomic features and improves with exercise; reflexes are decreased in LEMS.
• B. MG shows ocular symptoms only; LEMS presents with distal weakness and no autonomic features.
• C. MG presents with distal weakness that improves with rest; LEMS presents with fatigable ocular signs.
• D. MG has sensory loss; LEMS has pure motor deficits.

Answer: (C)

The main idea is that these two neuromuscular junction disorders differ in how weakness behaves with use and what features accompany it. Myasthenia gravis typically causes fatigable weakness that worsens with activity and often involves eye muscles, producing ptosis and diplopia; the weakness tends to improve with rest and after acetylcholinesterase inhibitors. Reflexes are usually normal. Lambert-Eaton myasthenic syndrome, by contrast, presents with proximal limb weakness and often autonomic symptoms; reflexes are reduced, and strength tends to improve with repeated use or exercise due to increased acetylcholine release with activity. Ocular involvement is less common in LEMS compared to MG.

So the best description is that MG shows fatigable weakness that worsens with use and frequently involves ptosis/ophthalmoplegia, while LEMS features proximal weakness with autonomic features and a notable improvement in strength with exercise, with reflexes decreased.