This article addresses questions of the pathogenesis of inflammatory and degenerative diseases of the nervous system using Parkinson’s disease, Alzheimer’s disease, and multiple sclerosis as examples. The commonality of the mechanisms of neurodegeneration in these diseases, based on results published in recent years, is discussed. The role of neurodegeneration as the leading process leading to persistent disability in patients with multiple sclerosis is assessed. The contributions of the inflammatory process and chronic infection to the manifestation and progression of neurodegenerative diseases are evaluated. Questions of the evidential basis of treatments atypical of these diseases are discussed in relation to the use of interferons, anti-inflammatories, statins, vitamin D, monoclonal antibodies, and correction of small intestinal dysbiotic processes in Parkinson’s disease and Alzheimer’s disease.