Examination confirms that both sides are involved, but it may not be until some weeks or months later that the patient is aware of the bilateral involvement so typical of the disease. ALS also does not affect sensation, which is a characteristic important in making the diagnosis. Multiple sclerosis, on the other hand, is usually asymmetrical in presentation and progression. Sensation can be and frequently is affected because of demyelination in those parts of the central nervous system where sensation is transmitted. Muscular dystrophies are diseases characterized by symmetrical distribution of muscular weakness and atrophy.
Sensation is completely unaffected.
These are not diseases of the central or peripheral nervous systems, but exclusively of muscle. The most widely known of the muscular dystrophies is Duchebbe's, which affects the child or adolescent, and the life duration is only a few years. On the other hand, myotonic muscular dystrophy affects the young adult and usually lasts longer than 20 years. There are forms of muscular dystrophic that result in minimal disability and do not significantly shorten life. The muscular dystrophies are hereditary.