Inflammatory Diseases of the CNS I: Encephalitis

Introduction Intracranial infections involving the bones of the skull or spine (osteomyelitis), the extradural compartments, the pachymeninges (dura), subdural space, leptomeninges and subarachnoid space are mainly caused by bacteria and occasionally by fungi and viruses (leptomeningitis). The organisms that infect the CNS itself (the brain and the spinal cord) are mainly viruses and bacteria, but fungi and protozoa, such as Toxoplasma and amoebae, do occasionally invade the CNS. Encephalitis can be defined as diffuse inflammation of brain tissue, or spinal cord (encephalomyelitis or just myelitis). Two major forms of encephalitis occur: those due to virus infections and those due to autoimmune inflammation Acute Disseminated Encephalomyelitis (ADEM).