A 10-year-old female has had diplopia and ptosis and weakness of her neck flexors for 2 months. Symptoms are worse in the evening and are usually partially improved on awakening in the morning. She has no fasciculations or myalgias, and her deep tendon reflexes are 1-2+. The most likely diagnosis is

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: C

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

Correct Answer: B

Rationale: In full-term newborns, mild hip and knee flexion contractures are normal due to in utero positioning and typically resolve by 4-6 months as the infant begins to move and stretch the joints.

Correct Answer: A

Rationale: A rocker-bottom foot is characteristic of congenital vertical talus, where the foot has a convex sole due to a fixed dorsiflexion of the talus.

Correct Answer: C

Rationale: A popliteal cyst (Baker's cyst) is a common benign condition in children, presenting as a firm mass in the popliteal fossa, more prominent on knee extension, with normal radiographs.