Muscular diseases, also known as muscular dystrophies, are a group of more than 30 genetic diseases--or in some cases, nongenetic diseases--that are characterized by the degeneration and weakness of skeletal muscles responsible for movement, according to the National Institute of Neurological Disorders and Stroke (NINDS). Some begin in infancy, while others appear later in life. They differ in the muscles they affect and the rate of progression.
Nongenetic Muscular Diseases
While a majority of muscular dystrophies stem from gene abnormalities, SingHealth states that two types of nongenetic muscle diseases exist--inflammatory and myasthenia gravis. Both of these diseases result from the body's attack on the immune system.
Inflammatory diseases, such as polymyositis, dermatomyositis and inclusion body myositis, are a result of the body's immune system damaging its own muscle tissue. In most cases these diseases affects adults; however dermatomyositis can affect children as well. Both polymyositis and dermatomyositis can be treated by suppressing the body's immune system with medication.
Myasthenia gravis is a muscular disease that results from the body's immune system injuring a special muscle structure--the acetylcholine receptor. Damage to these receptors is the cause of the symptoms of the disease, which include easy fatigue and weakness with exertion. This, too, can be treated effectively with drugs to suppress the immune system.
Duchenne Muscular Dystrophy
Duchenne is the most common muscular disease among boys, according to the MDA, typically occurring between the ages of two and six. This disorder first affects the upper arms and legs, as well as the pelvis. It tends to progress slowly, but can have moments of rapid spurts. The MDA states that most--but not all--boys with Duchenne are usually in a wheelchair by the age of 12, as the disease eventually affects all the muscles of the body. The University of Virginia Health system adds that survival beyond the age of 20 is rare.
Limb-Girdle Muscular Dystrophy
This type of muscular disease affects both males and females and usually begins during adolescence or early adulthood. Its progression is slow. It typically begins in the hips, moving up to the shoulders. Eventually the weakness includes a person's arms and legs as well. The MDA states that within 20 years of diagnosis, walking becomes difficult, if not impossible. The University of Virginia notes that death from this disease is generally from cardiopulmonary complications.
Distal Muscular Dystrophy
Distal muscular dystrophy is a group of rare muscular diseases that begin later in life--usually between the ages of 40 and 60, according to the University of Virginia Health System. These diseases cause wasting (thinning) of the muscles affected, usually in the forearms, hands, feet and lower legs, as the MDA states. These diseases progress slowly, rarely causing complete incapacitation. The MDA explains that Distal dystrophies are less severe and involve fewer muscles than other dystrophies. Walking can improve with devices that support the feet.
