Streptococcus sanguinis Endocarditis of Bicuspid Aortic Valve Presenting as Septic Arthritis of Lumbar Facet Joint

Septic arthritis of the facet joint (SAFJ) is an uncommon etiology of low back pain that usually affects the elderly population and immunocompromised patients but is rare in immunocompetent and young patients. When such a clinical presentation occurs, it is imperative to diagnose the source of the infection. We report a case of septic arthritis of the left third and fourth lumbar vertebrae facet joint due to Streptococcus sanguinis in a young immunocompetent adult, and the source of infection was found to be subacute infective endocarditis of a bicuspid aortic valve which was undiagnosed till now. A 49-year-old male presented with new-onset palpitations, dyspnea with exertion, low back pain, night sweats, and chills. A physical exam was significant for spinal tenderness on palpation of the lumbar spine around the L3-L5 level. Blood cultures were positive for Streptococcus sanguinis, and an MRI of the lumbar spine showed left-sided L3-L4 septic arthritis with epidural abscess and posterior paravertebral cellulitis/myositis. Transesophageal echocardiography led to the diagnosis of a bicuspid aortic valve and moderate aortic insufficiency, but it was a cardiac computed tomography that showed a sub-aortic valve abscess leading to the diagnosis of infective endocarditis. He was treated with a six-week course of intravenous antibiotics with complete resolution of symptoms, followed by aortic valve replacement with a mechanical valve. This case report focuses on the importance of diagnosing occult sources in clinically atypical infections, especially when hematogenous seeding is suspected.