Abstract
A 53-year-old man with steroid dependent rheumatoid arthritis presented with fever and serous articular drainage. Oral antibiotics were initially prescribed. Subsequent hemodynamic instability was attributed to septic shock. Further evaluation revealed a pericardial effusion with tamponade. Pericardiocentesis of purulent fluid promptly corrected the hypotension. Proteus mirabilis was later isolated from both the infected joint and the pericardial fluid. This is the first report of combined Proteus mirabilis septic arthritis and purulent pericarditis. It documents the potential for atypical transmission of Gram-negative pathogens, to the pericardium, in patients with a high likelihood of preexisting pericardial disease. In immunocompromised patients, the typical signs and symptoms of pericarditis may be absent, and the clinical presentation of pericardial tamponade may be misinterpreted as one of septic shock. This case underscores the value of a careful physical examination and proper interpretation of ancillary studies. It further illustrates the importance of initial antibiotic selection and the need for definitive treatment of septic arthritis in immunocompromised patients.