Myositis

Myositis is a rare disease that involves inflammation of the muscles. It can present with a variety of symptoms such as skin involvement (i.e., rashes), muscle weakness, and other organ involvement. Systemic symptoms such as weight loss, fatigue, and low fever can also present. Injury, medicines, infection, inherited muscle disease, or an autoimmune disorder can lead to myositis. It can also be idiopathic (no known cause). Injury - A mild form of myositis can occur with hard exercise. A more severe form of muscle injury, called rhabdomyolysis, is also associated with myositis. This is a condition where injury to the patient's muscles causes them to quickly break down. Medicines - A variety of different medicines can cause myositis. One of the most common drug types that can cause myositis is statins. Statins are drugs that are used to help lower high cholesterol. One of the most common side effects of statin therapy is muscle pain. Rarely, statin therapy can lead to myositis. Infection - The most common infectious cause of myositis is viral infections, such as the common cold. It can also include bacterial, parasitic, and fungal infections. Viruses, such as COVID-19, are also shown to be a rare cause of myositis. Benign acute childhood myositis has been described in children after prodromal viral infections with different viral agents. Inherited muscle disease - Many inherited myopathies may have secondary myositis, including calpainopathy, dysferlinopathy, fascioscapulohumeral muscular dystrophy, dystrophinopathy, and LMNA-associated myopathy. Autoimmune - Autoimmune disease is an abnormal immune response to a functioning body part, in this case the muscles. The three main types of idiopathic myositis (known as inflammatory myopathies) that typically test positive for autoantibodies are dermatomyositis, polymyositis, and inclusion body myositis. Other autoimmune diseases, such as systemic lupus erythematosus, can also cause myositis-like symptoms. There are various tools that can be used to help diagnose myositis.