A 12-year-old female experienced diarrhea, which lasted for 3 days, 2 weeks before manifesting progressive weakness and inability to walk. She has intermittent tingling of her fingers and toes. Physical examination reveals marked peripheral muscle weakness without atrophy or fasciculations. The deep tendon reflexes are absent in her ankles and 1+ at her knees. Findings on the sensory examination are normal. Motor involvement is symmetric. The most likely diagnosis is

Correct Answer: B

Rationale: Guillain-Barré syndrome (GBS) is characterized by a history of preceding infection (e.g., diarrhea), symmetric progressive weakness, areflexia, and sensory symptoms like tingling, without atrophy or fasciculations. Transverse myelitis typically involves sensory loss and asymmetric findings; polio causes asymmetric weakness with atrophy; myasthenia gravis features fatigable weakness without sensory symptoms; mononeuritis multiplex is focal and asymmetric.

Correct Answer: B

Rationale: Pompe disease (glycogen storage disease) causes cardiomegaly due to glycogen accumulation in the heart. Other conditions less commonly affect the heart this way.

Correct Answer: D

Rationale: Myasthenia gravis causes fatigable weakness (worse in evening), ptosis, diplopia, and neck weakness, with preserved reflexes. Other options lack fatigability or ocular symptoms.

Correct Answer: D

Rationale: All can cause weakness: hypothyroidism (myopathy), hyperparathyroidism (proximal weakness), corticosteroids (steroid myopathy), hyperaldosteronism (hypokalemia-related). Assuming intent, all are true, so E (moved to D) is least specific.

Correct Answer: C

Rationale: Ptosis and extraocular muscle weakness are the earliest and most consistent signs of myasthenia gravis due to ocular muscle involvement.