Successful methotrexate and rituximab combination therapy for a Taiwanese patient with anti-signal recognition particle antibody-positive immune-mediated necrotizing myopathy: a case report.

We report the successful use of methotrexate (MTX) and rituximab in a Taiwanese patient with anti-signal recognition particle (SRP) antibody-positive immune-mediated necrotizing myopathy (IMNM) refractory to conventional therapy. The patient was a 72-year-old Taiwanese woman. She had facial erythema, bilateral thigh muscle pain, dysphagia, and an abnormally high creatine kinase level and was admitted to our hospital. She tested positive for anti-SRP antibodies, lung ground-glass opacities on computed tomography, and a high signal in the muscle on magnetic resonance imaging of the thigh. Muscle biopsy revealed an absence of inflammatory cell infiltration and prominent necrotic and regenerative tissues. High-dose glucocorticoids, tacrolimus, and intravenous immunoglobulins were administered. Although the creatine kinase levels were temporarily decreased, tacrolimus induced thrombotic microangiopathy. The patient also developed dysphagia and respiratory muscle weakness, which required temporary positive-pressure ventilation. Rituximab was administered on Days 63, 74, 81, and 88, and then MTX was initiated. Dysphagia and respiratory and limb muscle weakness gradually improved, enabling glucocorticoid dose reduction. By Day 200, her creatine kinase level had improved, and she was weaned off the ventilator. Herein, we report the case of a Taiwanese East Asian patient with anti-SRP antibody-positive IMNM who was refractory to conventional therapy and was successfully treated with MTX and rituximab.