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Many of these diseases are genetic. Sometimes the cause is a medical condition such as alcoholism, a tumor, or a stroke. Other causes may include toxins, chemicals, and viruses. Sometimes the cause is not known. Degenerative nerve diseases include. 1  Alzheimer's disease. 2  Amyotrophic lateral sclerosis.
Many diseases previously classified as degenerative are now known to be associated with specific metabolic deficiencies or have other definite causes (Table 24-1). Others are transmitted by infectious agents (see Chapter 25). However, we are still left with a large number of progressive diseases of unknown etiology, and their classification is based on pathologic and clinical findings. This is true of many of the disorders of the basal ganglia and the rest of the extrapyramidal system.