The key finding in myotonic dystrophy in a newborn is dysfunctional muscle relaxation. Which description best matches this?

• A. Prolonged muscle contraction after stretch
• B. Prolonged muscle relaxation
• C. Hyperreflexia
• D. Fasciculations

Answer: (B)

The main idea being tested is myotonia—the delayed relaxation of skeletal muscle after contraction. In myotonic dystrophy, the muscle membrane remains hyperexcitable after a burst of activity, so the muscle takes longer to return to its resting length. That’s why the best description is prolonged muscle relaxation: after a contraction or quick stretch, the muscle does not promptly relax.

Hyperreflexia isn’t typical here because this is a myopathy with normal or decreased reflexes rather than an upper motor neuron–type hyperreflexia. Fasciculations are random twitches from motor unit instability and aren’t the hallmark of myotonic dystrophy.