Acquired OC, although rare, can occur as a result of neurologic abnormalities, and its diagnosis is dependent on an understanding of all causes of altered ventilation, including sleep disturbances--central, obstructive, or mixed. A neurologic evaluation, appropriate radiologic studies, and sleep workup will in most cases delineate the problem. Treatment includes a tracheotomy and ventilator support. Phrenic nerve pacing is reserved for patients with long-term disease and viable phrenic nerves.