Which statement about MG is true?

Which statement about MG is true?

• A. Myasthenia gravis causes fluctuating skeletal muscle weakness that worsens with fatigue and heat.
• B. Spinal muscular atrophy causes fluctuating weakness with exertion.
• C. Motor neuron disease presents with isolated diastolic hypertension.
• D. Hypertension is common in MG.

Answer: (A)

Fatigable weakness that worsens with use and improves with rest is a hallmark of myasthenia gravis, an autoimmune disorder of the neuromuscular junction. In MG, antibodies (often against acetylcholine receptors or related proteins) reduce the safety margin of transmission at the neuromuscular junction, so muscle response declines with repeated use and with higher temperatures. This makes weakness fluctuate and be accentuated by activity and heat, which is why this statement is true. Spinal muscular atrophy, by contrast, involves progressive motor neuron loss leading to steadily worsening proximal weakness rather than weakness that waxes and wanes with exertion. Motor neuron disease (ALS) mixes upper and lower motor neuron signs and isn’t characterized by isolated diastolic hypertension. Hypertension isn’t a defining feature of MG, either.

Fatigable weakness that worsens with use and improves with rest is a hallmark of myasthenia gravis, an autoimmune disorder of the neuromuscular junction. In MG, antibodies (often against acetylcholine receptors or related proteins) reduce the safety margin of transmission at the neuromuscular junction, so muscle response declines with repeated use and with higher temperatures. This makes weakness fluctuate and be accentuated by activity and heat, which is why this statement is true.

Spinal muscular atrophy, by contrast, involves progressive motor neuron loss leading to steadily worsening proximal weakness rather than weakness that waxes and wanes with exertion. Motor neuron disease (ALS) mixes upper and lower motor neuron signs and isn’t characterized by isolated diastolic hypertension. Hypertension isn’t a defining feature of MG, either.