South African flag sign to a giant coronary artery aneurysm.

Background: Coronary arteritis leading to aneurysm is one of the unusual presentations of IgG4-related disease. Acute myocardial infarction as a complication of IgG4-related giant coronary artery aneurysm is even rarer.

Case Summary: We describe the case of a 56-year-old gentleman who presented to our institute with Canadian Cardiovascular Society (CCS) class III angina. His symptoms were persistent even with high-dose antianginal medications. He had an acute coronary syndrome two weeks back for which he was treated conservatively in a peripheral health centre. His 12-lead electrocardiogram at the time of the event was suggestive of high lateral ST-segment elevation myocardial infarction (South African flag sign). His transthoracic echocardiography showed mild left ventricular dysfunction and a large echogenic mass lateral to the left ventricle. Coronary angiography followed by cardiac computed tomography revealed a giant pseudoaneurysm of the proximal and mid-left anterior descending coronary artery. FDG-PET scan showed significant metabolic activity in the aneurysm wall and mediastinal lymph nodes suggesting active inflammation. IgG4-related coronary arteritis was suspected, and the patient underwent aneurysmectomy and coronary artery bypass (CABG) surgery. The histopathology of the resected segment showed diffuse IgG4-secreting plasma cells confirming the diagnosis.

Discussion: Atherosclerosis is the most common cause of coronary aneurysms in adults. However, cardiologists should be aware of atypical causes like IgG4-related disease that can even present with acute coronary syndrome. Although multimodality imaging is beneficial during early evaluation, histopathological analysis is the cornerstone for the diagnosis of IgG4-related disease. The management involves both immunosuppressive medication and endovascular or surgical repair.