A wide variety of diseases affect the muscular system. Genetic disorders, such as the muscular dystrophies, typically present in children. Inflammatory and autoimmune diseases, such as polymyositis and myasthenia gravis, usually are of adult onset. All diseases that affect the muscular system cause muscle weakness. The muscles affected, and the associated symptoms and prognoses differ according to the specific disorder.
Muscular Dystrophy
Muscular dystrophy is an inherited abnormality of the muscles that causes progressive muscle cell damage and death. Progressive weakness accompanies muscle cell loss. The National Institute of Neurological Disorders and Stroke (NINDS) states there are more than 30 known types of muscular dystrophy with different patterns of inheritance and prognoses. Duchenne muscular dystrophy is the most common form of the disease and occurs in approximately one in every 3,500 males born in the United States, according to NINDS. Males are affected because the defective gene is passed from mother to son. Weakness of the hips, upper legs and shoulders typically presents in the toddler years. The Centers for Disease Control and Prevention notes symptoms in young children most often relate to hip and leg weakness, including frequent falls, difficulty climbing stairs, tired legs and walking with the legs widely spread apart. Children with Duchenne muscular dystrophy may have learning and behavioral difficulties, although this is not uniformly the case.
Myasthenia Gravis
Myasthenia gravis is an autoimmune disease in which the immune system destroys the communication between voluntary muscles and the nerves that control them, causing progressive muscle weakness. The Myasthenia Gravis Foundation of America reports common symptoms of the disease include drooping eyelids, blurred or double vision, chewing and swallowing difficulties, slurred speech, and arm and leg weakness. The muscles used for breathing can be affected, causing shortness of breath. According to NINDS, myasthenia gravis most commonly affects women younger than age 40 and men older than age 60.
Polymyositis
Polymyositis is a chronic inflammatory disease of the voluntary muscles. Inflammation is a normal body response to infection and injury. However, when inflammation occurs persistently and without provocation, the sites involved sustain progressive damage. The American Academy of Neurology notes the large muscles closest to the trunk of the body, such as the thigh, shoulder and upper arm muscles, typically demonstrate weakness with polymyositis. Common symptoms include struggling to get from a sitting to a standing position, difficulty climbing stairs and walking uphill, and difficulty performing overhead tasks. Involvement of muscles within the chest can cause swallowing and speech difficulties. Respiratory muscles may also be affected, leading to shortness of breath. NINDS reports polymyositis most commonly affects adults in the third through fifth decades of life.
References
- National Institute of Neurological Disorders and Stroke: Muscular Dystrophy: Hope Through Research
- Genetics Home Reference: DMD
- National Institute of Neurological Disorders and Stroke: How Do the Muscular Dystrophies Differ?
- Centers for Disease Control and Prevention: Duchenne Muscular Dystrophy Fact Sheet
- National Institute of Neurological Disorders and Stroke: Myasthenia Gravis Fact Sheet
