Baker's cyst with bacterial infection in a patient with recently diagnosed systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder characterized by the production of numerous pathologic autoantibodies. Patients with SLE are at increased risk of infection because of the disease course or treatment-related immunodeficiency. Infection is a major cause of morbidity and mortality among patients with SLE. Infected Baker's cyst (BC) can occur in patients with trauma, and degenerative or inflammatory arthritis, but is rarely described in SLE patients. We describe the case of a 22-year-old woman with a three-month history of SLE who did not receive any immunosuppressive treatment after diagnosis. Initial manifestations included fever, tachycardia, and hypotension with pain and edema in her left calf. Magnetic resonance imaging revealed a large BC with thickening of the adjacent subcutaneous layer of the calf. Turbid fluids were aspirated from the cyst, and methicillin-susceptible Staphylococcus aureus was cultured. She received antibiotic therapy and surgical drainage of the abscess. The patient recovered after 4 weeks of therapy. Early diagnosis, timely surgical intervention and use of antibiotics are important for reducing mortality associated with BC with infection.