A 6-year-old recovering from chickenpox becomataxic and unable to walk, with normal exam otherwise. The most likely diagnosis is

Correct Answer: C

Rationale: Post-varicella cerebellar ataxia is a common, self-limited complication in children, onset days after chickenpox, causing acute ataxia with normal cognition. Encephalitis involvfever and altered mentation. Thrombosis causfocal deficits. Demyelination (e.g., ADEM) is rarer, often post-vaccination. Chorea involvmovements, not ataxia. Cerebellar ataxias viral link makes C the correct answer.

Correct Answer: B

Rationale: Full-term infants exhibit flexion of lower and upper extremiti, per neonatal norms, due to physiologic flexor tone from corticospinal immaturity. Fencing posture is asymmetrical tonic neck reflex, not resting state. Mixed flexion-extension (C-D) or full extension suggest hypotonia or prematurity. Flexion reflects healthy tone, making B the correct answer.

Correct Answer: C

Rationale: Visual acuity reach20/20 by 6 months , per AAP, as retina and visual cortex mature, allowing fine discrimination. Earlier (A-B, 2-4 months) acuity is ~20/200; later (D-E, 8-10 months) refinfurther. Six months marks this milestone, making C the correct answer.

Correct Answer: C

Rationale: Steppage gait results from common peroneal nerve palsy, per neurology texts, with high stepping to clear the foot due to dorsiflexor weakness (foot drop). Shuffling is parkinsonian; tandem tests balance; toe walking spasticity. Steppagcompensation makes C the correct answer.

Correct Answer: A

Rationale: Axonal neuropathidiminish NCV amplitude, per neurophysiology, from axon loss reducing signal strength. Guillain-Barré slows velocity (demyelination); botulism and myasthenia affect junctions, not amplitude; viral meningitis is unrelated. Axonal pathology makes A the correct answer.