Diseases

Abstract

Diseases affecting the nervous system encompass a broad spectrum of disorders which induce, for example, abnormalities of motor, sensory, vision, taste, olfaction, sleep, memory, cognitive functions, or behavior. They may involve primarily the nervous system or may be part of a general disorder (infectious disease, cancer…). They can be of genetic, environmental, or mixed, often still partly obscure, mechanisms. Their diagnosis may be easily performed by the usual clinical examination (history taking and physical evaluation such as assessment of gait, muscle power testing, deep tendon reflexes evaluation…), but a number of modern investigations, such as neuroimaging, metabolic, or genetic studies are now widely used. These diseases benefit by the outburst of knowledge in the neurosciences. The heavy cost and high degree of disability that some of these conditions induce, along with their rising occurrence and associated increased life expectancy, in most countries induce a major public health concern. As an example, the prevalence (number of affected persons) of Alzheimer disease (see Sect. 4.2.10) is estimated to increase from 1.5 % in the age group 65–70 to 6 % in for people age 75–80, and over 25 % above 85 years of age.