A 12-year-old female experiencacute monocular blindness of 2 days duration. Past history includuncharacterized headachfor 3 years, one episode of diplopia, and one of paresthesias of the feet, unrelated in time. Physical exam is unremarkable except reduced visual acuity. The most important diagnostic step is

Correct Answer: B

Rationale: MRI is the most important step for acute monocular blindness lasting 2 days, with prior headaches, diplopia, and paresthesias. This suggests a neurologic etiology like migraine with prolonged aura, demyelination (e.g., MS), or stroke. MRIs superior soft-tissue resolution detects white matter lesions, infarcts, or inflammation, critical for differential diagnosis. CT identifihemorrhage but misssubtle pathology. EEG assessseizures, irrelevant here without convulsion. Nerve conduction and biopsy target peripheral nerves, not central vision loss. MRIs diagnostic yield, per AAN guidelines, make B the correct answer, addressing the broad symptom spectrum.

Correct Answer: A

Rationale: Simple partial seizurlack loss of consciousness , per ILAE, preserving awareness during focal motor (versive, B), sensory, or autonomic events lasting 10-20 seconds without postictal confusion . Abnormal EEG is typical. Loss of consciousness defincomplex partial seizures, not simple ones. This awareness distinction, rooted in seizure classification, makes A the exception and correct answer.

Correct Answer: A

Rationale: Migraine variants include cyclic vomiting , amaurosis fugax , alternating hemiplegia , and confusional stat, per ICHD-3, tied to migraine pathophysiology. Cluster headachare a distinct trigeminal-autonomic cephalalgia, not a migraine variant, with different featur(e.g., unilateral autonomic signs). This nosologic separation makes A the exception and correct answer.

Correct Answer: A

Rationale: Sydenham chorea, post-streptococcal, featurhypotonia with milkmaids grip , choreic hand , darting tongue , and emotional lability , reflecting basal ganglia dysfunction. Hypertonia contradicts choreas flaccid, involuntary nature; rigidity suggests other conditions (e.g., dystonia). This motor distinction, per rheumatic fever literature, makes A the exception and correct answer.

Correct Answer: A

Rationale: Frontal lobe lesions cause reappearance of grasp and rooting reflexes, per neurology texts, due to loss of inhibitory control from prefrontal areas. These frontal release signs emerge in adults with dementia or stroke, not typically occipital (B, vision), parietal (C, sensation), temporal (D, memory), or cerebellar (E, coordination) damage. Neonatal reflexvanish by 6 months as cortex matures; their return signals frontal dysfunction. This localization, rooted in cortical maturation, makes A the correct answer.