Thrombotic microangiopathy in a patient with anti-signal recognition particle antibody–positive immune-mediated necrotising myopathy: a case report

Thrombotic microangiopathy (TMA) is a rare but life-threatening complication in idiopathic inflammatory myopathies. Although TMA has been increasingly recognised in anti-melanoma differentiation-associated gene 5 antibody-positive dermatomyositis, it remains exceptionally uncommon in anti-signal recognition particle (SRP) antibody-positive immune-mediated necrotising myopathy (IMNM). We describe a 62-year-old woman with anti-SRP antibody-positive IMNM who developed rapidly progressive TMA shortly after the initiation of immunosuppressive therapy, including tacrolimus. At presentation, she exhibited early proteinuria, severe myositis activity, and markedly elevated creatine kinase levels. Despite prompt high-dose corticosteroids, rapid withdrawal of tacrolimus, plasma exchange, intravenous immunoglobulin, and rituximab, her TMA progressed to dialysis-dependent acute kidney failure, although she ultimately survived and was successfully weaned from mechanical ventilation. To our knowledge, this represents only the second reported case of TMA associated with anti-signal recognition particle antibody-positive IMNM. Patients with highly active IMNM and early renal involvement may be particularly vulnerable to calcineurin inhibitor-associated TMA, and clinicians should exercise caution when introducing these agents in such settings. Early recognition of proteinuria, thrombocytopenia, and laboratory features of hemolysis may facilitate a timely diagnosis and guide appropriate therapeutic intervention.