Extragenital Mycoplasma hominis infection following obinutuzumab therapy in a patient with chronic lymphocytic leukemia.

Mycoplasma hominis is a fastidious, cell wall-deficient bacterium that typically colonizes the genitourinary tract but can cause invasive extragenital infections in immunocompromised hosts. Such infections have been reported primarily in patients receiving rituximab; however, they have not been previously described with obinutuzumab therapy. We report a case of M. hominis septic arthritis of the shoulder in a 70-year-old man with chronic lymphocytic leukemia/small lymphocytic lymphoma treated with Obinutuzumab. The patient presented with several months of progressive shoulder pain and radiographic evidence of rapidly destructive arthritis. Repeated joint aspirations and early cultures were negative, and he required multiple surgical washouts because of extensive purulence and periarticular abscess formation. Extended incubation of synovial fluid and tissue cultures ultimately identified M. hominis. Antimicrobial therapy was transitioned to levofloxacin and doxycycline, which were administered for six weeks with good tolerance and sustained clinical improvement. At follow-up, the patient remained free of recurrent infection with gradual recovery of shoulder function. This case highlights M. hominis as an emerging opportunistic pathogen in patients receiving newer anti-CD20 monoclonal antibodies and expands the recognized infectious complications of obinutuzumab-induced B-cell depletion. Because M. hominis lacks a cell wall, routine diagnostic methods and empiric β-lactam therapy may be ineffective, resulting in diagnostic delays. Awareness of this organism and early consideration of targeted therapy are critical to improving outcomes in immunocompromised patients.