Some disorders commonly cause dysfunction of parts of both the peripheral and the central nervous system. This often leads to complex syndromes that may affect many neural functions. When these disorders affect the peripheral nervous system, they most often cause polyneuropathy, which may occur alone, or which often precedes involvement of the central nervous system. When these disorders affect the central nervous system, they usually affect diffuse areas of the cerebral cortex. A few of these disorders may cause focal lesions of the central nervous system. Several types of pathology may cause mixed central and peripheral neurological disorders, including idiopathic, infectious, nutritional, and toxic disorders.