More Than Skin Deep: Loculated Pericardial Effusion Causing Localized Cardiac Tamponade Due to Cutibacterium acnes Pericarditis

Acute pericarditis, or inflammation of the pericardial sac, is a common cause of chest pain with a broad range of etiologies, including viral, bacterial, traumatic, rheumatologic, and malignant causes; however, most cases are idiopathic. Acute pericarditis is associated with the development of a pericardial effusion in many patients. In rare cases, the effusion may progress to cardiac tamponade, a life-threatening condition in which increased intrapericardial pressure impairs cardiac filling through external compression of the cardiac chambers. Pericardial effusions are typically circumferential, and tamponade is classically recognized by compression of the lower-pressure right-sided cardiac chambers. However, atypical presentations can occur in which the left-sided chambers are primarily affected. Prompt recognition of this condition is essential to facilitate urgent or emergent pericardiocentesis. We present the case of a 73-year-old man with a history of coronary artery bypass grafting (CABG) who developed a loculated pericardial effusion causing localized cardiac tamponade, necessitating urgent pericardiocentesis. Subsequent pericardial fluid cultures grew Cutibacterium acnes (C. acnes) , a common skin colonizer that was considered the causative organism of infective pericarditis based on the patient's clinical presentation. This report highlights the atypical echocardiographic findings of a loculated pericardial effusion causing localized cardiac tamponade. It also highlights the diagnostic difficulty in determining whether C. acnes is a pathogenic organism.