Demyelination is often secondary to an infectious, ischemic, metabolic, or hereditary disorder or to a toxin (eg, alcohol, ethambutol). In primary demyelinating disorders, cause is unknown, but an autoimmune mechanism is suspected because the disorder sometimes follows a viral infection or viral vaccination.
For other uses, see Realm (disambiguation). A realm /ËrÉlm/ is a community or territory over which a sovereign rules; it is commonly used to describe a kingdom or other monarchical or dynastic state. The Old French word reaume, modern French royaume, was the word first adopted in English; the fixed modern spelling does not appear until the beginning of the 17th century.
The Neotropical realm is one of the eight biogeographic realms constituting the Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone.