Common disorders of the muscular system include polymyositis, inclusion body myositis, muscular dystrophy and metabolic muscle disorders, according to LiveScience. Other muscle disorders come about from overuse of the muscles, including strains and sprains, says MedlinePlus.
Polymyositis is an inflammatory, autoimmune disease that attacks the muscles and weakens them, states MedicineNet. As with other immune diseases, polymyositis sufferers endure relapses and flare-ups that happen after long periods where the patient is asymptomatic or in remission. Sometimes, a rash accompanies the disease. In that case, it is called dermatomyositis.
Inclusion body myositis is another chronic, inflammatory muscle disease, according to the National Institute of Neurological Disorders and Stroke. It is a progressive disease that weakens the muscles and often affects just one side of the patient's body. In some patients, the first symptoms are felt in the hands when the fingers can't grasp as well as they should. As of 2015, there is no treatment for inclusion body myositis.
Muscular dystrophy is a genetic disease that causes the patient to lose muscle mass over time, claims Mayo Clinic. This leads to increasing weakness that can result in the patient losing the ability to walk or even to breathe. Most types of muscular dystrophy begin when the patient is a child.