Common variable immunodeficiency presenting as a Mycoplasma hominis septic arthritis.

A case is reported of common variable immunodeficiency (CVID) presenting as an acute septic arthritis due to Mycoplasma hominis. The diagnosis was not considered until the hypogammaglobulinaemia was discovered and the synovial fluid cultured specifically for mycoplasmas. The importance of diagnosing immunodeficiency states and searching for mycoplasmas in 'bacteriologically culture negative' cases is emphasized.