[Atlantoaxial dislocation with ventilatory insufficiency--report of two cases]

We performed electromyography and polysomnography in two cases of atlantoaxial dislocation with ventilatory insufficiency to determine the patients' respiratory patterns. The results showed that hypertrophic sternocleidomastoid muscles (SCMs) played an important part in their respiration. The diaphragm and intercostal muscles did not display marked electromyographic (EMG) activity, but the SCMs showed a great deal of phasic inspiratory activity during the daytime that decreased or disappeared during sleep. A 6-year-old boy with atlantoaxial dislocation related to spinal abnormalities was chiefly dependent on the SCMs for respiration and required mechanical ventilation when a sleep because the SCMs were completely inactive. A 4-year-old girl with atlantoaxial dislocation as the result of an automobile accident was partially dependent on the SCMs. She had no trouble breathing during the daytime, but polysomnography recordings showed recurrent hypopnea and desaturation during the night synchronous with decreased EMG activity of the SCMs. She also required mechanical ventilation to improve her long-term prognosis. Polysomnography should be performed in severe cases of atlantoaxial dislocation with respiratory failure in addition to routine respiratory function tests.