[Clinical reasoning and decision-making in practice. A 31-year-old woman with transient monocular blindness and polycythaemia].

A 31-year-old woman presented with recurrent transient monocular blindness. As transient ischaemic attacks were suspected further investigations were targeted at evaluation of premature atherosclerotic lesions in the internal carotid artery. Initially laboratory tests were not performed. After referral to a cardiovascular-disease prevention outpatient clinic, laboratory evaluation disclosed a marked isolated polycythaemia that turned out to be secondary to right-left shunting through multiple pulmonary arteriovenous malformations. The ultimate diagnosis was hereditary haemorrhagic telangiectasia. Later on, physical signs such as telangiectasia and central cyanosis were noticed. In the clinical decision-making process, laboratory tests associated with causes of transient monocular visual loss were not carried out and therefore clues important for the ultimate diagnosis were not obtained. In only a minority of young patients with transient monocular visual loss can this be ascribed to premature atherosclerosis. For these reasons, a proper physical examination and laboratory tests directed towards other causes must be part of the initial diagnostic work-up in young patients with visual disturbances and suspected transient ischaemic attacks.