Mycoplasma hominis septic arthritis in a patient with hypogammaglobinaemia and rheumatoid arthritis

Abstract

We describe the case of Mycoplasma hominis septic arthritis in a 58-year-old woman with a history of rheumatoid arthritis and ulcerative colitis on immunosuppressive therapy with rituximab. Treatment with anti-CD20 antibodies (eg, rituximab) leads to an immediate depletion of B cells and hence risk of reductions in immunoglobulins and increased risk of infections. This effect may last long after drug cessation. M. hominis is commensal to the genitourinary tract in sexually active adults. Extragenital M. hominis infections including septic arthritis are rare, but hypogammaglobulinaemia is a predisposing factor. As M. hominis requires extended culture, special media or PCR analysis, it is not tested routinely, which in many cases delays diagnosis and correct treatment. In our case, a diagnosis of M. hominis septic arthritis was made after 9 weeks by PCR analysis and culture of joint fluid. The patient responded well to an 8-week treatment course of moxifloxacin and doxycycline.

Keywords: bone and joint infections; drugs: infectious diseases; immunology.

Figure 1

Repeated treatment with rituximab can cause hypogammaglobulinaemia. The patient in this case received rituximab due to rheumatoid arthritis and immunoglobulin levels were last controlled 11 days before the first admission when the patient showed the first symptoms of infection. The next control of immunoglobulin levels was almost 11 weeks later and showed reduced levels of IgG and IgM. The patient received treatment with monthly immunoglobulin.

Figure 2

The trend in C reactive protein throughout the course of disease shows a marked decline since the initiation of dual therapy with moxifloxacin and doxycycline. The patient also experienced consistent improvement.