Degenerative muscle diseases cause progressive damage and loss of muscle cells with associated weakness. There are many types of degenerative muscle diseases, and they act in different ways to cause loss of functional muscle mass. The muscular dystrophies, amyotrophic lateral sclerosis, myasthenia gravis, and other inherited and acquired diseases cause muscle degeneration. The symptoms of degenerative muscle diseases relate to progressive weakness in the affected muscle groups.
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Degenerative muscle diseases that affect the large muscles of the legs and buttocks characteristically cause walking difficulties. Duchenne muscular dystrophy, the most common of the muscular dystrophies, is one such disease. Children with Duchenne muscular dystrophy exhibit walking difficulties from an early age. They often walk with the legs spread widely apart and frequently stumble or fall due to weakness of the upper leg muscles. As the disease progresses and muscle weakness increases, the ability to walk is eventually lost. The National Institute of Neurological Disorders and Stroke (NINDS) reports that most children with Duchenne muscular dystrophy are wheelchair-bound by 12 years of age.
Loss of Muscle Strength
The loss of muscle cells associated with degenerative muscle diseases causes progressive and often profound loss of strength in the affected muscles. This symptom is characteristic of all degenerative muscle diseases, although the muscle groups exhibiting the most pronounced weakness vary from one disease to another. For example, NINDS notes myasthenia gravis commonly affects the muscles of the eyes and face, causing drooping eyelids and odd or diminished facial expression. In contrast, people with amyotrophic lateral sclerosis or Lou Gehrig's disease may present with weakness of the fingers and hands that causes difficulty with tasks such as writing, opening jars or buttoning a shirt.
Loss of muscle mass increases the workload on the remaining muscle cells, which are typically in suboptimal condition because of the disease process. The result is easily induced muscle fatigue, often with minimal muscular activity. “The Merck Manual for Healthcare Professionals” explains that myasthenia gravis is a special case regarding this symptom in that the muscles show a measurable decline in strength upon use. With rest, the muscles return to pre-use strength only to rapidly fatigue again when used.
Speech, Chewing and Swallowing Difficulties
Degenerative muscle diseases that affect the muscles of the mouth and throat typically cause speech, chewing and swallowing difficulties. The Myasthenia Gravis Foundation of America notes that these symptoms are common with myasthenia gravis. Facioscapulohumeral muscular dystrophy and amyotrophic lateral sclerosis also frequently cause speech and swallowing difficulties, according to NINDS.
Degenerative muscle diseases involving the chest muscles cause breathing difficulties. Often the onset of involvement of the respiratory muscles in a degenerative muscle disease heralds the imminent demise of the afflicted person. People with severe involvement of the respiratory muscles typically require ventilator support.