Use of Tocilizumab to Treat Arthritis Associated with Mixed Connective Tissue Disease Complicated by Ovarian Teratoma: A Case Report.

Mixed connective tissue disease (MCTD) is characterized by mixed features of systemic lupus erythematosus, systemic sclerosis, and polymyositis/dermatomyositis and is rare in children. Here, we report a case of MCTD in a 10-year-old girl who presented at our hospital with arthralgia, Raynaud's phenomenon, and fatigue. Blood tests were positive for anti-U1-ribonucleoprotein (RNP) antibodies and for rheumatoid factors (RFs) IgG-RF and anti-galactose-deficient IgG. Levels of myogenic enzymes and hypergammaglobulinemia were elevated. Macrophages were prominent in bone marrow, with scattered phagocytic macrophages. MCTD was diagnosed based on the patient's symptoms and laboratory findings. Methylprednisolone pulse therapy combined with oral tacrolimus was administered, which led to resolution of symptoms. Three months after pulse therapy, arthralgia worsened and methotrexate was administered. Arthralgia improved but did not resolve. Magnetic resonance imaging performed to investigate the hip pain revealed a mature ovarian teratoma, which was surgically removed. Because the pain persisted and interfered with her daily life, she was treated with tocilizumab for joint pain relief, which decreased the pain level. Tocilizumab is a candidate for additional treatment of juvenile idiopathic arthritis-like arthritis associated with childhood-onset MCTD.