When Steroid Injection Meets Rituximab: Disseminated MSSA

Background: Septic arthritis is a rare but potentially fatal complication of intra-articular corticosteroid injection, commonly caused by Staphylococcus aureus. The risk is higher in older adults and those with diabetes, rheumatoid arthritis (RA), immunosuppression, or a history of recent joint procedures. Diagnostic delay is possible, as non-infectious arthritis can present with similar features. Although rituximab is generally considered safe, rituximab-associated hypogammaglobulinemia may increase susceptibility to severe infections. We report a case of methicillin-sensitive Staphylococcus aureus (MSSA) septic arthritis with hematogenous vertebral seeding following intra-articular corticosteroid injection in a patient receiving rituximab therapy. Case: A 73-year-old man with seropositive RA, treated with prednisone, methotrexate, hydroxychloroquine, and rituximab, presented with one week of progressive knee pain, swelling, and erythema following an intra-articular corticosteroid injection performed several days earlier. He met criteria for severe sepsis. Arthrocentesis revealed purulent fluid, and cultures grew MSSA, consistent with blood culture results. The patient underwent two surgical washouts and received intravenous cefazolin. During hospitalization he developed new thoracic back pain. Magnetic resonance imaging demonstrated T5-T6 osteomyelitis/discitis with early epidural phlegmon, consistent with hematogenous spread. Blood cultures cleared after six days of antibiotic treatment and source control, and he completed eight weeks of intravenous antibiotic therapy. Discussion: Intra-articular corticosteroid injections can precipitate rapidly progressive septic arthritis with potential for distant seeding, particularly in immunosuppressed individuals. Early arthrocentesis, prompt source control, and surveillance for secondary foci, including vertebral osteomyelitis, are critical. Infection risk assessment prior to rituximab initiation and judicious use of intra-articular injections in high-risk patients are recommended.