Disseminated septic arthritis caused by Ureaplasma urealyticum in an immunocompromised patient with hypogammaglobulinemia after rituximab therapy

Abstract

Purpose: Ureaplasma urealyticum is a rare pathogen associated with septic arthritis that predominantly affects patients with hypogammaglobulinemia. Bacterial identification of fastidious organisms is challenging because they are undetectable by routine culture testing. To the best of our knowledge, this is the first report of septic arthritis induced by U. urealyticum infection in Japan.

Case description: We describe the case of a 23-year-old Japanese female with secondary hypogammaglobulinemia (serum immunoglobulin level < 500 mg/dL), identified 8 years after treatment with rituximab. The patient presented with persistent fever and polyarthritis that were unresponsive to ceftriaxone and prednisolone. Contrast-enhanced computed tomography and gallium-67 scintigraphy revealed effusion and inflammation in the left sternoclavicular, hip, wrist, knee, and ankle joints. Although Gram staining and bacterial culture of the drainage fluid from the left hip joint were negative, the condition exhibited characteristics of purulent bacterial infection. The patient underwent empirical treatment with doxycycline, and her symptoms promptly resolved. Subsequent 16S ribosomal RNA (rRNA) gene sequencing of the joint fluid confirmed the presence of U. urealyticum, leading to the diagnosis of septic arthritis. Combination therapy with doxycycline and azithromycin yielded a favorable recovery from the inflammatory status and severe arthritic pain.

Conclusion: This case highlights U. urealyticum as a potential causative agent of disseminated septic arthritis, particularly in patients with hypogammaglobulinaemia. The 16S rRNA gene analysis proved beneficial for identifying pathogens in culture-negative specimens, such as synovial fluid, in suspected bacterial infections.

Keywords: Ureaplasma urealyticum; 16S rRNA gene sequencing; Hypogammaglobulinemia; Joint infection; Rituximab; α-Defensin.

Fig. 1

Radiological findings A, B Contrast-enhanced computed tomography showing effusions in the left sternoclavicular and both hip joints. C Gallium-67 scintigraphy demonstrating uptakes in bilateral wrist, knee, ankle joints, and large joints. D Magnetic resonance imaging of the hips detecting bone marrow edema along with fluid retention bilaterally

Fig. 2

The clinical course of the patient Serum C-reactive protein levels decreased following DOXY therapy and resurged after switching to LVFX. Combination therapy with DOXY (MINO) and AZM was effective, and the patient was discharged with AZM monotherapy. PSL prednisolone; CRP C-reactive protein; IVIG intravenous immunoglobulin; DOXY doxycycline; MINO minocycline; LVFX levofloxacin; AZM azithromycin