The locked-in syndrome (LIS) results from an extended lesion in the brain stem, generally at the level of the protuberance. This lesion affects the long tracts crossing the brain stem, as well as the vital centres and the nuclei of certain cranial nerves in the fourth and twelfth pair. The LIS patient is perfectly conscious, but trapped in the shackles of a motionless body.
There are three forms of locked-in syndrome:
- classic LIS, where the patient is limited to a vertical movement of the eyes and opening and closing the eyelids;
- incomplete LIS, where there is some remaining voluntary movement in the limbs;
- complete LIS, where the patient is totally motionless, including eye movements.