ABSTRACT
In this chapter we will discuss an approach towards making a pathological diagnosis of cases of progressive dementia with onset in adult life. Dementia, by definition, involves the loss of previously acquired higher mental capabilities, and needs to be distinguished from mental retardation, where such capacities had never developed. Dementia may occur in childhood, but there it is due to a rather different range of disorders than are found in adults. However, it should be noted that rare adult onset cases of inherited metabolic diseases, while more commonly occurring in childhood, may present with dementia in the adult years. Further, there are many diseases in which dementia may occur in the adult as part of the overall clinical picture, such as in cases of multiple sclerosis (MS), diffusely infiltrating primary brain tumors or progressive multifocal leukoencephalopathy (PML). Such cases are not our concern here, though they may be expected to turn up as rare examples of unexplained dementia. The overwhelming majority of adult patients in which the clinical picture is dominated by progressive deterioration of cognitive function will be found to be suffering from one of the conditions discussed in this chapter.
