A 69-year-old male patient, presented in mid-September 2018, with oligoarticular joint pain that progressed over a 3 week period and affected the right knee as well as the right elbow and the right shoulder. Symptoms were associated with morning stiffness lasting 30 min, as well as nocturnal pain. There was no history of trauma, upper respiratory tract infection or recent traveling abroad. There were no practice of risky sexual behaviour, and no recalling of any tick bites or animal encounters. His medical history is relevant for cutaneous psoriasis, type 2 diabetes mellitus, and Non-Hodgkin lymphoma in remission since 2012 after a hematopoietic stem cell autograft. Upon presentation the patient had no fever. His right knee showed a spontaneous flexum with effusion made evident by a positive Flot and Glaçon sign. Left and right shoulder mobility were both limited. A left pre-pectoral Port-a-cath showed no signs of redness or swelling. The rest of the physical exam in the emergency department was unremarkable. Initial biological work-up showed elevated CRP levels of 299 mg/dL, with mild leukocytosis. Serum chemistries and the coagulation panel were unremarkable. Blood cultures were also drawn upon admission, despite no signs of hyperpyrexia. Arthroscopic drainage of the right knee was performed on the basis of suspected septic gonarthritis. Biochemical analysis of the synovial fluid revealed 50,000 elements with 64% neutrophils, without crystals. The patient was then started on an empirical antimicrobial regimen consisting of amoxicillin-clavulanate. Joint fluid cultures and blood cultures remained sterile after 14 days. Over the course of the following days, the patients condition deteriorated, with fever and sequential multiple joint swelling involving the metacarpophalangeal joints of both hands, the proximal interphalangeal joints of the digits as well as the right elbow. Physical examination showed signs of right-sided heart failure with a new proto-systolic murmur of 3/6 intensity that was most prominent in the right second parasternal intercostal space. Bilateral pitting edema was present in the pre-tibial regions. Examination of the extremities revealed no signs of distal embolization or subcutaneous nodules. The neurological exam was normal. Biological studies at week 2 showed worsening of the inflammatory biomarkers with a CRP level of 340 mg/dL, an erythrocyte sediment rate of 90 mm/h as well as normocytic hypochromic anaemia and thrombocytosis. The rest of the panel showed hyperferritinemia, a positive rheumatoid factor, as well as elevated liver enzymes. Anti-CCP antibodies were negative. Ultrasound of the small joints revealed various degrees of synovitis in the tarses, both wrists as well as the elbows. A 16 × 9 mm mobile vegetation of the posterior mitral valve leaflet, protruding into to the left ventricle without signs of left ventricular failure, septal abscess or mitral valve regurgitation was visualized on transthoracic echocardiography. Extensive workup for endocarditis by means of multiple hemocultures, optic fundoscopy, cerebral imaging with CT and MRI, serologies for Coxiella burnetti, Brucella spp, Bartonella spp and Tropheryma whipplei, and antinuclear antibody panel with dosage of anti-phospholipid antibodies were all negative. The search for an oral cavity source of the endocarditis was both done clinically and through the use of an orthopantomogram. None were identified after thorough examination. A cervico-thoraco-abdomino-pelvic injected CT was performed and excluded a relapse of the NHL. Eubacterial PCR of the synovial fluid sampled from the right knee during admission arthoscopy was performed retrospectively and came back positive for Mycoplasma salivarium. A transesophageal echocardiography was carried out 48 h later and confirmed the presence of the vegetation and revealed minimal pericardial effusion. Intravenous amoxicillin-clavulanate was replaced by IV ceftriaxone and oral doxycyclin. The antibiotic regimen was then further restricted to moxifloxacin as a final choice, after long QTc was excluded by 12-lead ECG. Figure shows the evolution of C-reactive protein (CRP) after introduction of specific antimicrobial directed therapy. Full antimicrobial regimen was administered for a total of 6 weeks. A follow up transthoracic echocardiography after 14 days of antibiotics showed almost complete regression of the vegetation. Distant embolisation given the rapid regression of the vegetation was excluded by means of cerebral MRI and a PET-CT. PET-CT imaging revealed a hypermetabolic foci on the mitral valve, comforting our initial diagnostic hypothesis of infective endocarditis. The patient recovered completely after a long stand of antibiotic treatment. He continues to show persistent signs of remission to this day.