Primary Sjogren's syndrome with tuberculous arthritis of left knee.

A 56-year-old woman presented with recurrent pain and swelling of left knee, Raynaud's phenomenon and dry mouth. She was initially diagnosed with primary Sjögren's syndrome and was put on prednisone, which substantially relieved her complaints. But 8 months later, pain and swelling of left knee recurred with spiking fever, chills and shortness of breath. Escalation of prednisone did not improve the pain and swelling of left knee. CT of chest revealed pulmonary interstitial changes with coexisting infection. MRI of left knee was highly consistent with tuberculous arthritis, which was further confirmed by positive blood culture of Mycobacterium tuberculosis and acid-fast stain of synovial fluid.