Abstract
Arthritis is one of the major complications in mixed connective tissue disease (MCTD)． It is mostly
presented with non-erosive, mild-to-moderate synovitis． We describe a MCTD case of 14-years-old girl、who
had a shoulder pain during MTX therapy for refractory constitutional symptoms at three years after onset．
Arthroscopy revealed pannus formation with massive bone erosive area， which was a close resemble to
synovitis in rheumatoid arthritis． She was diagnosed as MTX-resistant arthritis with MCTD and was
successfully treated with synovectomy followed by tocilizumab， an effective biologics for rheumatoid arthritis．
This case reminds us the importance of practical interventions based on pathophysiologic features, especially
when facing multisystem disorders such as collagen diseases． Also suggests tocilizumab has a therapeutic
potential for treating arthritis with collagen diseases．
