The patient is a 50-year-old female with no significant personal medical history, cardiovascular risk factors, or family history of cardiac diseases. She reports a one-month history of worsening exertional dyspnea and postural lightheadedness. She now presents to the emergency department following a syncopal episode while standing. She denies any palpitations, chest discomfort, or diaphoresis. Cardiovascular, pulmonary, and neurological examinations are unremarkable. 

Electrocardiography found diffuse ST-segment depression with aVR lead ST-segment elevation. High-sensitivity troponin-T was raised at 127 ng/L. 

Urgent coronary angiography was performed, which showed subtotal left main coronary artery (LMCA) tapered occlusion with TIMI 1 flow and collaterals from the right coronary artery. Plain balloon angioplasty was performed with lumen and flow restoration. Intravascular vascular ultrasound (IVUS) showed extraluminal encasement LMCA and ostial left anterior descending artery with thickening of the adventitia surrounded by extraluminal masses and multiple microchannels.

Laboratory tests showed low C3 and C4  complements with raised Immunoglobulin G4 subclass levels. Transthoracic echocardiography showed preserved left ventricular ejection fraction and no resting regional wall motion abnormalities. 18F-Positron emission tomography (PET) with contrast-enhanced multi-slice computed tomography (CT) with myocardial suppression showed FDG-avid circumferential thickening of the aortic root extending along the LMCA, pulmonary trunk, and carotids. Mild FDG-avidity was seen in the supra- and infra-diaphragmatic lymph nodes and spleen. High-dose prednisolone was initiated with plans for subsequent coronary reassessment.

ImmunoglobulinG4-related disease (IgG4-RD) is a multiorgan chronic fibroinflammatory disordercharacterized by dense plasma cell infiltration. Here, we describe a rare caseof symptomatic LMCA stenosis from isolated periaortic IgG4-RD.Coronaryarteritis should be considered in individuals with unusual or indolent presentationswithout atherosclerotic risk factors. Concerns for in-stent restenosis mayarise if the underlying inflammatory disease is uncontrolled. During initialangiography, IVUS may help characterize perivascular disease. As histopathologicaldiagnosis is challenging, serum immune markers with multimodality imagingtechniques, especially PET, can help affirm the diagnosis.