Approach to complications of prematurity (late) Quiz: Ace Your Exams

An 18-month-old boy is evaluated at a well child visit. The parents are concerned because the child is cruising but not yet walking. A friend's daughter began walking around 12 months of age. The patient was born at 29 weeks’ gestation with a birth weight of 1,350 grams. The pregnancy was complicated by eclampsia requiring emergency cesarean delivery. The infant was in the Neonatal Intensive Care Unit (NICU) and discharged at 3 months of age. The hospital course was complicated by respiratory distress syndrome, grade III intraventricular hemorrhage without calcifications, and anemia that required multiple transfusions. Other developmental milestones are appropriate for age. The infant passed a repeat hearing screen at 12 months. Follow-up with ophthalmology shows no concerns. Weight, height, and head circumference are at the 20^th percentile for age on the World Health Organization growth curve. Temperature is 37°C (98.6°F), pulse is 105/min, respirations are 25/min, blood pressure is 83/36 mm Hg, and oxygen saturation is 98% on room air. The anterior fontanelle is closed. Physical exam is notable for hypertonia, spastic lower extremities, and hyperreflexia but is otherwise unremarkable. Which of the following diagnostic measures would best help to determine the underlying cause of this patient’s developmental delay?