― Progressive Dementia ∙ In most chronic cognitively impaired older adults, the observed deterioration is not secondary to a reversible disease or to drug reactions. The underlying cause of chronic, progressive deterioration of cognitive functioning is an irreversible change in the structure and function of the brain. An estimated 5% of adults 65 years of age and older suffer severe, chronic, irreversible cognitive impairment. Another 5% exhibit moderate degrees of impairment. [...].