Calcium and Parathyroid USMLE Step 1 Practice Question
A 3-year-old girl is brought to the emergency department by her parents after experiencing a 2-minute generalized tonic-clonic seizure at home. She has a history of recurrent infections treated with antibiotics over the past 18 months and was noted to have developmental delay starting around age 18 months. Physical examination reveals characteristic facial features including micrognathia, short philtrum, and low-set ears. Vital signs: HR 120/min, RR 26/min, BP 95/58 mmHg, Temp 37.1°C. Laboratory studies show: serum calcium 6.9 mg/dL (normal 8.5-10.5), phosphate 7.1 mg/dL (normal 2.5-4.5), PTH 12 mIU/L (normal 15-65), magnesium 1.8 mg/dL (normal 1.7-2.2). A chest X-ray is obtained. Which of the following findings on chest imaging would most strongly support the diagnosis?
Answer choices
- AAbsent or hypoplastic thymic shadow with normal cardiac silhouetteCorrect answer
- BCardiomegaly with pulmonary congestion and normal thymic shadow
- CRight aortic arch with coarctation of the aorta
- DAnterior mediastinal mass with displacement of the trachea
- EHyperinflation with peribronchial infiltrates suggestive of aspiration
- FNormal chest X-ray with incidental finding of thymic hyperplasia
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