Myopathy associated with anti-signal recognition particle antibodies with pulmonary involvement and response to rituximab

The authors present the case of a 76-year-old female patient with progressive decrease in proximal muscle strength, fatigue, dyspnea, diffuse hand edema and painful triphasic Raynaud’s phenomenon. Anti-SRP and anti-SSA antibodies were detected, muscle biopsy revealed changes consistent with necrotizing myopathy and capillaroscopy had findings compatible with systemic sclerosis. High-resolution chest computed tomography revealed interstitial lung disease with a non-specific interstitial pneumonia pattern. Lung function tests demonstrated a forced vital capacity 93% and a diffusing capacity for carbon monoxide of 65% predicted. After multidisciplinary discussion, she was diagnosed with immune-mediated necrotizing myopathy/systemic sclerosis overlap syndrome with pulmonary involvement. Initially, dual immunomodulation therapy with high-dose steroids and intravenous immunoglobulin was started, but after 4 weeks, the patient had clinical and analytical deterioration. At this time, she was started on rituximab, with an excellent and sustained response at both muscle and lung, sustained after 12 months.