Bilateral hypoglossal nerve palsy due to vertical subluxation of the odontoid process in rheumatoid arthritis.

Two patients with rheumatoid arthritis involving the cervical spine developed a rapidly progressive dysarthria due to bilateral hypoglossal nerve palsies, in one patient as an isolated lesion, and in the other in conjunction with dysfunction of the vagus and glossopharyngeal nerves. Both patients showed upward movement of the axis, relative to the foramen magnum, which has been termed 'vertical subluxation of the odontoid' or 'cranial settling'. Mechanical injury to the nerves, secondary to this process, is the most likely mechanism.