Anti-SRP-positive necrotising myopathy concurrent with breast malignancy

Anti-signal recognition particle (anti-SRP)-positive necrotising myopathy causes severe progressive proximal weakness with a propensity to involve pharyngeal, laryngeal and respiratory muscles. It is one of the aggressive inflammatory myopathies. First-line treatment is with high-dose steroids followed by other immunosuppressants, but this conventional therapy is often ineffective. Second-line treatment involves use of either rituximab or intravenous immunonoglobulin (IVIG). Anti-SRP-positive necrotising myopathy is frequently treated as refractory myositis due to its poor responsiveness to steroid monotherapy and conventional immunosuppressive therapies. Therefore, anti-SRP-positive necrotising myopathy differs from immune-mediated myopathy. Although anti-SRP autoantibody is found in only 4-6% of patients with idiopathic inflammatory myopathy, the actual proportion of patients with refractory anti-SRP-positive necrotising myopathy is unknown. We describe a patient with multiple comorbidities who had subacute-onset anti-SRP-positive immune-mediated necrotising myopathy (IMNM). After failing steroids, methotrexate and IVIG therapy, she made a considerable recovery with rituximab. She was later diagnosed to have breast malignancy. Malignancy-associated anti-SRP-positive IMNM is rarely reported.