Microorganisms in Pathogenesis and Management of Necrotising Autoimmune Myopathy (NAM) and Inclusion Body Myositis (IBM)

This chapter aims to describe two clinical-pathological alterations of the muscles, named, respectively, necrotizing autoimmune myopathy (NAM) and inclusion body myositis (IBM). Both conditions have an inflammatory-immunological background, and they result from specific interactions between genetic and environmental risk factors. Histologically, NAM is characterized by muscle fibre necrosis in the absence of prominent inflammatory infiltrate, whereas IBM present in vacuoles within which there are clumps of protein. We paid specific attention to the role of microbes in taking part in the pathogenetic process. Due to current pandemic, we focused on SARS-CoV-2 infection. Considering that myalgia, muscle weakness and increased serum Ck levels are common during COVID-19 infection, it is difficult to distinguish simple muscle damage secondary to infection or an autoimmune SARS-CoV-2-triggered myositis with consequent diagnostic and therapeutic delay. In view of the growing importance of microbiome's involvement in autoimmune disorders, we tried to find any possible link between its alterations and the development of NAM or IBM, but, so far, literature is very scant. To better understand the pathogenesis and to offer new therapeutic options, further research on this subject is needed.