Diseases that affect the human body's muscular system include genetic disorders such as muscle dystrophy and cancers such as soft tissue sarcoma, according to MedlinePlus. Glycogen-storage diseases, tetany and myotonia congenita can also affect the muscular system, notes Encyclopædia Britannica.
Muscle dystrophy refers to several muscle diseases in which abnormal genes cause muscle loss and weakness. Most forms of muscle dystrophy are congenital diseases and affect a majority of boys, notes Mayo Clinic. Myotonia congenita is a type of muscle dystrophy that causes the enlargement and increased stiffness of muscles. Tetany is another medical condition that affects the muscular system by causing uncontrollable spasms in the muscles involving the arms, legs and voice box, according to Encyclopædia Britannica. Muscular atrophy is one indication of the presence of a muscular system disease.
Soft tissue sarcoma is a cancer that affects soft tissues, including the muscles, nerves, fat and blood vessels. Many types of soft tissue sarcomas develop in the arms and legs, states the American Cancer Society. Smooth muscle and skeletal muscle tissue tumors affect how the body's muscles work. Rhabdomyosarcomas are a type of malignant skeletal muscle tumor that commonly affects the arms and legs. Unlike leiomyosarcomas, another type of malignant tumor affecting smooth muscles, rhabdomyosarcomas affect children more often than adults.