Diseases

Inflammation or swelling of a muscle, usually a voluntary muscle, caused by injury or infection.

Persons most commonly affected: Adults, usually over 50 years. More so in men then women.
Organ or part of body involved: Muscles
Symptoms and indications: Early signs are extreme fatigue after prolonged walking or standing, weakness of arms, legs and hands, especially thighs, wrists and fingers. The muscle weakness is proximal (closest) to and within the trunk and most likely affects the neck, back, hip, buttocks and thigh muscles as well as the shoulder and upper arm muscles. In some cases swallowing can be difficult. Rare cases involve heart and lung involvement.
Causes and risk factors: The cause of myositis is not known. Myositis is an autoimmune disease. In myositis, autoimmunity leads to inflammation of specific muscles. This inflammation results in muscle damage and may lead to muscle cell death. Many different muscle groups may be involved in the disease ranging from muscles of the arms and legs to those of the respiratory and gastrointestinal systems. In addition, the abnormal immune response can lead to other problems including, damage to blood vessels, joints, lungs, and the heart.