Although the etiology of MS is unknown, it is best described as an inflammatory disorder resulting in scattered neuron demyelination. The most frequently postulated theory for MS is a genetic predisposition triggered by a virus (such as herpes or HTLV-1) or environmental toxins that induce an immune-mediated neuronal inflammation and demyelinization.10 MS causes a dysfunction in oligodendrocytes such that the axonal myelin sheaths are damaged, slowing nerve impulse conduction. These scattered cerebral and spinal plaques cause gliosis primarily in the white matter, with relative axon sparing.
These plaques occur in multiple areas, including the cerebrum, brainstem, spinal cord, and cranial nerves. The brain may have variable amounts of atrophy and ventricular dilatation. Nerves in the corticospinal tracts, posterior columns, and spinothalamic tracts will cause upper motor neuron, proprioception/vibration, and pain/temperature dysfunction, respectively. Cranial nerve dysfunction most often causes optic neuritis, but facial motor and sensory deficits are also common.
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