摘要:Introduction. Infectious and autoimmune rheumatic diseases (ARDs) are closely linked. Apart from the challenging, sometimes differential, diagnosis between these conditions, it is recognized that microbes play an important role in the pathogenesis of the latter. Material and method. We present the case of a 45-year-old female patient from our rehabilitation department, with complex pathology (infectious, neurological, rheumatological and orthopedic pathology) that began more than 15 years ago. The patient’s pathological history began insidiously at theage of 30 when she was diagnosed with neurotoxoplasmosis. She received anticoagulant, antiepileptic, steroidal, antibiotic and antihelmintic treatment. After four years, the patient shows insidious onset of inflammatory pain in the large joints and in 2010 is diagnosed with seropositive rheumatoid arthritis, according to American College of Rheumatism/European League against rheumatism (ACR/EULAR) criteria with symmetric impairment of the large joints (shoulder, elbow, hip, knee, ankle). Despite the treatment with disease-modifying anti-rheumatic drugs (DMARDs) received, in the following years she needed 4 arthroplasties in the large joints due to osteonecrosis. Conclusions. On clinical grounds, infections, especially chronic infections, can cause a plethora of autoimmune phenomena, thus mimicking ARDs. Therefore, the differential diagnosis between ARDs and infectious diseases is sometimes challenging as they often display similar clinical manifestations. It is highlighted that the immune system can be our friend or our foe considering that its function and dysregulation are the common denominators in autoimmune and infectious diseases. In the era of new drugs and new therapeutic strategies, safety of the patients should always be our first concern.