Fatal Cardiomyopathy Secondary to Seronegative Immune-Mediated Necrotizing Myopathy: A Case Report.

A 35-year-old man presented with proximal muscle weakness and myalgias that led to a diagnosis of seronegative immune-mediated necrotizing myopathy (IMNM).

• The patient was previously healthy prior to presentation.
• Initial workup revealed elevated creatinine kinase and inflammatory markers.
• MRI demonstrated findings of proximal muscle inflammation.
• Muscle biopsy was diagnostic of IMNM.
• Serologic testing was negative for anti-SRP and anti-HMGCR, confirming seronegative IMNM.

The patient subsequently developed acute heart failure complicated by ventricular tachycardia as a rare cardiac complication of seronegative IMNM.

• Cardiac positron emission tomography demonstrated an inflammatory myocardial process.
• Endomyocardial biopsy demonstrated interstitial fibrosis with macrophages.
• Cardiac involvement in idiopathic inflammatory myopathies is described as uncommon.
• The patient developed progressive cardiogenic shock and cardiac arrest.

Multiple immunosuppressive and cardiac treatment modalities failed to prevent disease progression and death.

• Initial treatment included high-dose glucocorticoids, methotrexate, and intravenous immunoglobulin.
• Additional treatment modalities included rituximab, mycophenolate mofetil, and cyclophosphamide.
• Advanced cardiac therapies were also employed.
• Despite all interventions, the patient developed progressive cardiogenic shock and ultimately died.

Clinical cardiac involvement in seronegative IMNM likely conveys a poor prognosis, and effective treatments for this patient population are not understood.

• This case is described as a fatal, treatment-refractory cardiomyopathy secondary to seronegative IMNM.
• The authors note it is 'not understood what treatments are effective in this patient population, presenting opportunities for further study.'
• Cardiac involvement is described as an uncommon complication of IIM broadly.
• The authors suggest this case presents opportunities for further study of this rare complication.