A 6-month-old infant presents with severe hypotonia and generalized weakness, his creatine phosphokinase (CK) is mildly elevated, the electromyelogram (EMG) shows fasciculations and fibrillations, muscle biopsy specimens show grouped atrophy. Of the following, the MOST likely finding in this infant is

Correct Answer: A

Rationale: Absent deep tendon reflexfit spinal muscular atrophy (SMA), per pediatric neurology, with hypotonia, weakness, mild CK elevation, and EMG/biopsy showing denervation (fasciculations, grouped atrophy). Sensation is spared; ptosis myasthenic; cognition normal; Moro irrelevant. Reflex loss from anterior horn cell loss makes A the correct answer.

Correct Answer: B

Rationale: Dandy-Walker malformation featurvermis agenesis, fourth ventricle cyst, and enlarged posterior fossa, per radiology texts. Corpus callosum agenesis affects midline; holoprosencephaly forebrain; hydranencephaly cortex loss. Triad specificity make B the correct answer.

Correct Answer: D

Rationale: Postinfectious acute cerebellar ataxia is the most common cause of acute childhood ataxia, per pediatrics, often post-viral (e.g., varicella). Strokand MS are rare; postictal transient; tumors chronic. Postinfectious frequency makes D the correct answer.

Correct Answer: C

Rationale: Stupor is responsiveness to pain only, per neurology, with reduced arousal beyond lethargy or obtundation . Coma lacks response; consciousness full. Stupors definition makes C the correct answer.

Correct Answer: C

Rationale: Choroid plexus papilloma caushydrocephalus from CSF overproduction, per neurosurgery, as a rare tumor hypersecretfluid. Craniopharyngioma obstructs; aqueductal stenosis blocks; basilar impression compresses; Dandy-Walker malforms. Overproduction specificity makes C the correct answer.