Covid-19–Associated Myopathy Caused by Type I Interferonopathy

Abstract

Caused by Type I Interferonopathy][3] Whether the elevation in creatine kinase level is caused by viral infection of muscle, toxic effects of cytokines, or another mechanism is unclear.There are few reports of muscle-biopsy findings in patients with Covid-19. 4We describe a patient with Covid-19 infection and myopathy who had a muscle-biopsy specimen showing evidence of virus-induced type I interferonopathy.A 38-year-old man who had no recent history of illness or medication use presented with weakness, myalgias, and fever.He had generalized muscle weakness, which was more severe proximally than distally, and was unable to walk, abduct his shoulders, or flex his hips against gravity.Heliotrope rash, Gottron's sign or papules, and nail-bed changes were absent.He had bibasilar infiltrates and a positive reverse-transcriptase-polymerase-chain-reaction assay for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA.The serum level of creatine kinase was 29,800 U per liter (reference range, 39 to 308), high-sensitivity troponin T 3157 ng per liter (reference range, 0 to 14), and C-reactive protein 55 mg per liter (reference value, <10), and myoglobinuria was not present.Findings on electrocardiography, echocardiography, and cardiac magnetic resonance imaging were normal.A description of the methods used for the immunohistochemical analysis of muscle is provided in the Supplementary Appendix, available with the full text of this letter at NEJM.org.A biopsy specimen of his left deltoid muscle showed mild perivascular inflammation in a few vessels but no necrotic or regenerating fibers or perifascicular atrophy.Immunohistochemical

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