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Pulmonary arteriovenous malformations — SCE Respiratory MCQ

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HardPulmonary vascular diseasePulmonary arteriovenous malformationsSCE Respiratory

A 34-year-old man with recurrent epistaxis has exertional dyspnoea and oxygen saturation of 88% on air. Chest CT shows multiple peripheral pulmonary arteriovenous malformations. His mother had a stroke aged 41 and similar nosebleeds. ABG confirms hypoxaemia with a normal PaCO2. What is the most likely underlying cause?

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Correct answer: D — Right-to-left shunting through pulmonary arteriovenous malformations

The best answer is “Right-to-left shunting through pulmonary arteriovenous malformations”. The clinical pattern, physiology and imaging described are most consistent with Right-to-left shunting through pulmonary arteriovenous malformations. The competing diagnoses may share individual findings, but do not account for the complete combination in the stem. The remaining choices—“Ventilation-perfusion mismatch from asthma, after specialist assessment”, “Reduced inspired oxygen pressure, with clinical reassessment”, “Alveolar hypoventilation from obesity, within a respiratory pathway”, “Diffusion limitation from interstitial fibrosis, after safety review”—are credible in related respiratory presentations, but each addresses a different diagnostic, staging or management decision and does not fit the decisive findings and pathway position in this stem.

Reference: British Thoracic Society guideline for home oxygen: https://thorax.bmj.com/content/70/Suppl_1/i1