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Locked-in syndrome is a condition in which a patient is aware and awake but cannot move or communicate due to complete paralysis of nearly all voluntary muscles in the body except for the eyes.

It is the result of a brain stem lesion in which the ventral (anterior) part of the pons is damaged. The term for this disorder was coined by Fred Plum and Posner in 1966.

Locked-in syndrome is also known as cerebromedullospinal disconnection, de-efferented state, pseudocoma and ventral pontine syndrome.

Presentation

Locked-in syndrome usually results in quadriplegia and the inability to speak in otherwise cognitively intact individuals. Those with locked-in syndrome may be able to communicate with others through coded messages by blinking or moving their eyes, which are often not affected by the paralysis.

The symptoms are similar to those of sleep paralysis. Patients who have locked-in syndrome are conscious and aware with no loss of cognitive function. They can sometimes retain proprioception and sensation throughout their body. Some patients may have the ability to move certain facial muscles, most often some or all of the extraocular eye muscles.

Individuals with locked-in syndrome lack coordination between breathing and voice. This restricts them from producing voluntary sounds, even though the vocal cords themselves are not paralysed.

Causes

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:

• Traumatic brain injury
• Diseases of the circulatory system
• Medication overdose
• Damage to nerve cells
• A stroke or brain haemorrhage, usually of the basilar artery

Treatment

There is no standard treatment for locked-in syndrome, nor is there a cure. Stimulation of muscle reflexes with electrodes (NMES) has been known to help patients regain some muscle function.

Other courses of treatment are often symptomatic. Assistive computer interface technologies, such as Dasher in combination with eye tracking may be used to help patients communicate. New direct brain interface mechanisms may provide future remedies. Israeli scientists have reported that they have developed a technique that allows locked-in patients to communicate via sniffing.