Compared to patients who die without COVID-19 infection, patients who die with severe COVID-19 may show signs of mild to severe myositis, suggesting that SARS-CoV-2 may be associated with a post-infectious, immune-mediated disease, according to the study Myopathy can be linked Findings published in JAMA Neurology.
Mild to fatal myopathies have been associated with a number of viruses; However, muscle biopsies are not often done when viral-associated myositis is suspected. A team of researchers in Germany performed a case-control autopsy series as a multidisciplinary post-mortem analysis to examine myocardial and skeletal muscle inflammation in patients with COVID-19 or other critical illnesses who died between March 2020 and February 2021.
Study researchers measured skeletal muscle tissue inflammation by quantifying immune cell infiltrates, expressing major histocompatibility complex (MHC) class I and II antigens on sarcolemma, and performed a blinded assessment on a visual analog scale from no detected pathology to significant pathology by.
A total of 43 patients with COVID-19 (mean age 72 years; men 72%) and 11 patients with other critical illnesses than COVID-19 (mean age 71 years; men 64%) were included in the analysis.
Compared to patients with other critical diseases, skeletal muscle samples from patients who had COVID-19 at the time of death had an overall higher pathology score (mean 1.5 vs. 3.4; P <0.001) and a higher inflammation score (mean 1.0 vs 3.5 or P <0.001).
Of the 42 samples from patients with COVID-19, relevant expressions of MHC class I antigens and MHC II antigens on sarcolemma were present in 55% and 17% of the samples, respectively. However, relevant terms were not found in any of the control samples.
Compared to control samples, the number of natural killer cells in samples from patients with COVID-19 was increased (mean value 3 vs. 8 cells per 10 high-power fields; P <0.001). There was also more inflammatory features in skeletal muscles than heart muscles, and inflammation was highlighted in patients with COVID-19 with a chronic history.
Although SARS-CoV-2 ribonucleic acid was found in some muscle samples, direct viral infection of the myofibers was not evident either in immunohistochemistry or in electron microscopic analyzes.
“Evidence of viral load was low or negative in most skeletal and cardiac muscles and probably more likely to be due to circulating viral RNA than to real infection of myocytes,” the study researchers found.
“Whether these results can be transferred to milder disease courses and possibly explain chronic muscle fatigue syndromes, as they are described in post-acute COVID-19 syndromes, and whether autoimmune mechanisms are involved, must be investigated in future studies,” the authors concluded.
Disclosure: Several authors stated links to the pharmaceutical industry. For a full list of the details, see the original article.
T. Aschman, J. Schneider, S. Greuel et al. Relationship between SARS-CoV-2 infection and immune-mediated myopathy in deceased patients. JAMA Neurol. Published online June 11, 2021. doi: 10.1001 / jamaneurol.2021.2004