[Blastocystis hominis as a rare arthritogenic pathogen. A case report].

Blastocysts hominis, a protozoon considered to be a nonpathogen intestinal commensal, is now discussed to be a cause of intestinal infection under certain circumstances, e.g., immunosuppression. There are two published cases of Blastocysts infection complicated by arthritis which was classified as "reactive" in one case, "infectious" in the other. We report a third case: A 46-year-old female patient developed a chronic diarrhea and oligoarthritis some days after returning from a trip to Senegal. Arthritis was refractory against treatment with NSAID and corticosteroids. Finally, a 3-week course of treatment with metronidazole resulted in a complete remission of arthritis, gastrointestinal symptoms, and inflammation signs (ESR, CRP). The course in our case, as well as the detection of Blastocysts hominis in synovial fluid in another case, implicate an infectious rather than a reactive etiology of arthritis.