Locked-in syndrome is a rare neurological disorder in which there is complete paralysis of all voluntary muscles except for the ones that control the movements of the eyes. Individuals with locked-in syndrome are conscious and awake, but have no ability to produce movements (outside of eye movement) or to speak (aphonia). Cognitive function is usually unaffected. Communication is possible through eye movements or blinking. Locked-in syndrome is caused by damaged to the pons, a part of the brainstem that contains nerve fibers that relay information to other areas of the brain.
Unlike persistent vegetative state, in which the upper portions of the brain are damaged and the lower portions are spared, locked-in syndrome is caused by damage to specific portions of the lower brain and brainstem, with no damage to the upper brain.
Possible causes of locked-in syndrome include:
- Snakebite cases – More frequently from a krait bite and other neurotoxic venoms, as they cannot, usually, cross the blood–brain barrier
- Amyotrophic lateral sclerosis (aka Lou Gehrig’s disease)
- Brainstem stroke
- Diseases of the circulatory system
- Medication overdose, or central pontine myelinolysis secondary to rapid correction of hyponatremia
- Multiple sclerosis
- Damage to nerve cells, particularly destruction of the myelin sheath, caused by disease or central pontine myelinolysis secondary to rapid correction of hyponatremia [>1 mEq/L/h])
- A stroke or brain hemorrhage, usually of the basilar artery
- Traumatic brain injury