Which condition shows reflexes decreased and autonomic features with improvement with exercise?

Which condition shows reflexes decreased and autonomic features with improvement with exercise?

• A. Lambert-Eaton syndrome
• B. Myasthenia gravis
• C. Guillain-Barré syndrome
• D. Huntington disease

Answer: (A)

Reflexes that are reduced at rest but improve with sustained activity point to a presynaptic neuromuscular junction issue. In Lambert-Eaton myasthenic syndrome, antibodies target voltage-gated calcium channels on the motor nerve terminal, which lowers acetylcholine release. When you perform repetitive activity or brief bursts of exercise, more calcium enters the terminal, increasing acetylcholine release and briefly enhancing transmission. This leads to weakness with autonomic features and reflexes that improve with exercise. These autonomic symptoms—dry mouth, constipation, orthostatic changes—often accompany the motor findings. Myasthenia gravis, by contrast, typically shows fatigable weakness that worsens with use and doesn’t exhibit the same reflex facilitation after exercise. Guillain-Barré syndrome usually causes areflexia and may have autonomic instability, but strength and reflexes don’t improve with exercise. Huntington disease presents with chorea and cognitive changes rather than a neuromuscular junction–driven pattern of reflex changes and autonomic features. Thus, the described pattern best fits Lambert-Eaton myasthenic syndrome.

Reflexes that are reduced at rest but improve with sustained activity point to a presynaptic neuromuscular junction issue. In Lambert-Eaton myasthenic syndrome, antibodies target voltage-gated calcium channels on the motor nerve terminal, which lowers acetylcholine release. When you perform repetitive activity or brief bursts of exercise, more calcium enters the terminal, increasing acetylcholine release and briefly enhancing transmission. This leads to weakness with autonomic features and reflexes that improve with exercise. These autonomic symptoms—dry mouth, constipation, orthostatic changes—often accompany the motor findings.

Myasthenia gravis, by contrast, typically shows fatigable weakness that worsens with use and doesn’t exhibit the same reflex facilitation after exercise. Guillain-Barré syndrome usually causes areflexia and may have autonomic instability, but strength and reflexes don’t improve with exercise. Huntington disease presents with chorea and cognitive changes rather than a neuromuscular junction–driven pattern of reflex changes and autonomic features.

Thus, the described pattern best fits Lambert-Eaton myasthenic syndrome.