Myositis is inflammation of muscle tissue due to injury, infection or autoimmune disease.
Myositis can be caused by infection with the parasitic nematode Trichinella spiralis. You become infected with this worm by eating poorly cooked, infected pork. The larvae produced by mating male and female worms invade muscle cells. The disease is characterized by abdominal pain, cramping, muscle pain and diarrhea.
Other infectious agents, including influenza virus, HIV, Lyme borrelia, and tapeworm can cause myositis.
Dermatomyositis is an autoimmune connective tissue disease that is characterized by inflammation of muscle and skin. This disease affects women more than men and usually occurs in people 40-60 yrs old.
Polymyositis is an ideopathic inflammatory disease that does not involve the skin. The cause is unknown.
Myopathy is a term used to describe neuromuscular diseases that are characterized by muscle weakness but are not muscular dystrophy. These diseases can be due to abnormalities in mitochondria or glycogen storage, a problem in metabolizing myoglobin or due to toxic effects of hormones or chemicals. One example is the muscle weakness or necrosis that can occur in some individuals taking cholesterol-lowering statin drugs.
Rhabdomyolysis is the sudden necrosis of skeletal muscle with the release of large amounts of myoglobin into the circulation. Myoglobin can be toxic to the kidneys and can result in their shutdown. This disease can result from any injury to the muscles, especially trauma.