Summary

We describe a case of a previously healthy 58-year-old woman who presented with gradual onset shortness of breath on exertion, erythrocytosis, hypoxia and hypoxaemia. Initial investigations revealed a normal chest radiography and pulmonary function test, however, there was an isolated reduction in diffusion capacity. She was subsequently found to have a patent foramen ovale (PFO) with intermittent shunting. A contrast echocardiography study hinted towards an extracardiac shunt. No shunt was detected in spite of using advanced imaging techniques. A lung biopsy was ultimately performed and histopathology revealed diffuse microvascular pulmonary arteriovenous malformations. This is one of few cases reported of this rare vascular abnormality and highlights its strong genetic association with hereditary haemorrhagic telangiectasia. The diagnostic challenges and management of this unique condition are reviewed in detail.