Myositis
Flu complication: Myositis
Myositis when your immune system mistakenly attacks healthy tissue and causes your muscles to become inflamed.
Post-infectious reactive myositis occurs after viral infections.
After killing the virus, your immune system can cause inflammation in other parts of your body, including your muscles, for a few month.
Post-infectious reactive myositis is usually mild.
Post-infectious reactive myositis usually settles without treatment.
Sources
(1) http://www.nhs.uk/conditions/myositis/Pages/Introduction.aspx
(2) https://www.arthritisresearchuk.org/arthritis-information/conditions/polymyositis-and-dermatomyositis/related-condition.aspx