Myositis is a general term for inflammation of the muscles. Many such conditions are considered likely to be caused by autoimmune conditions, rather than directly due to infection (although autoimmune conditions can be activated or exacerbated by infections.) It is also a documented side effect of the lipid-lowering drugs statins and fibrates.
Elevation of creatine kinase in blood is indicative of myositis.
Read more about Myositis: Types