Abstract
Interleukin-6 receptor antagonist tocilizumab is a biologic drug used for treating patients with active rheumatoid arthritis (RA) who failed to respond to synthetic or other biologic disease-modifying antirheumatic drugs or where they were contraindicated. Interleukin-6 receptor blockade results in a decrease of disease activity but has some potential adverse effects, the most common being infections. We present a case of a 75-year-old female patient with long-lasting RA, several comorbidities and multiple prior therapies, who developed back pain and general malaise during tocilizumab intravenous treatment. The laboratory findings were typical of toxemia, and the imaging findings revealed large psoas muscle abscess. Surgical and antibiotic treatment was performed with a good outcome. To our knowledge, this has been the first case of a psoas abscess in a patient with RA treated with tocilizumab described in the literature so far. We also present a review of the literature regarding infection, and particularly abscess formation in patients treated with biological disease-modifying antirheumatic drugs, tocilizumab included.