Primary infectious costochondritis due to Prevotella nigrescens in an immunocompetent patient: clinical and imaging findings.

Infection of costal cartilage is a rare observation. We report the case of a 43-year-old male patient without relevant history who presented with a progressive painful swelling of the left chest wall since 4 months. Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated an abscess within the left ninth costal cartilage with surrounding reactive changes. A CT-guided biopsy was performed and the culture of the sample revealed the presence of Prevotella nigrescens. Musculoskeletal infections by Prevotella are rarely described in the literature, Prevotella oralis and Prevotella bivia being the most frequently observed pathogens. These infections usually originate from a hematogenous spread after thoracic surgery or dental procedure. In our patient, conservative treatment was chosen. A clinical improvement was noted after 1-month antibiotherapy, confirmed by short-term and 6-month imaging follow-up showing the complete disappearance of all previously observed abnormalities.