Environmental Risk Factors for Myositis in Military Personnel

Background: * Myositis is a rare disease in which the body s immune cells attack the muscle tissue. It can cause muscle weakness, swelling, and pain. It can develop in people with no history of muscle problems. Environmental exposures may determine who develops myositis. Genes may also affect development of the disease. * Some people who serve in the military develop myositis. However, other military personnel do not. Researchers want to compare military personnel with and without myositis. They will look for common factors that might have led to the disease. Objectives: \- To study environmental risk factors for myositis in military personnel. Eligibility: * Military personnel who developed myositis during their period of service. * Healthy military personnel who do not have myositis or another autoimmune disease. Design: * Participants will have a physical exam and medical history. * Participants will fill out forms about environmental exposures, particularly while in the military. The questions will ask about past infections, vaccines and medications, and personal habits. They will also ask about participants occupations during military service and their deployments. * Participants will also provide blood samples for study. * No treatment will be provided as part of this study.