The nuclei of CN XI or XII may be involved in a number of disease processes including motor neuron disease, poliomyelitis, brain stem abscess, and syringobulbia. y In addition to muscle weakness, these lesions may result in atrophy and fasciculations. Bilateral involvement of these nuclei may result in diminished ability to rotate the neck, inability to protrude the tongue, slurred and indistinct speech, impaired swallowing, and possibly some respiratory difficulty. The medial medullary syndrome, which is caused by occlusion of the vertebral artery, results in paralysis and atrophy of the tongue on the side of the lesion (due to involvement of the twelfth cranial nerve or nerve nucleus), weakness of the arm and leg on the side opposite the lesion (due to involvement of the pyramidal tracts before their decussation), and impaired tactile and proprioceptive sense of the side of the body opposite to the lesion (due to involvement of the medial lemniscus). y , '29'
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