Locked-in syndrome

Locked-in syndrome (LIS), also known as pseudocoma, is a condition in which a patient is aware but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in their body except for vertical eye movements and blinking. This is due to quadriplegia and bulbar palsy. The person is conscious and sufficiently intact cognitively to communicate with eye movements. Electroencephalography results are normal in locked-in syndrome as these people have retained brain activity such as sleep-wake cycles and attention that is detectable. Fred Plum and Jerome B. Posner coined the term in 1966. Locked-in syndrome can be separated into subcategories based on symptom severity. This consists of classic locked-in syndrome, characterized by the inability to move distal limbs and facial muscles, but retained ability to blink and move eyes vertically, with preserved cognition and consciousness. Incomplete locked-in syndrome is less severe than classic locked-in syndrome and shares similar preserved abilities as classic locked-in syndrome, but has the hallmark of additional motor abilities, whether that be in the muscles innervating the limbs or face. Complete locked-in syndrome contains the conserved cognition and consciousness as classic locked-in syndrome, but has additional motor deficits that render the individual unable to move their eyes vertically or blink. Locked-in plus is an additional form distinguished by impairments to cognition and consciousness, but contains damage to similar regions of the brainstem affected by other forms, notably the pons, with the addition of other cortical and subcortical regions.

Signs and symptoms Locked in syndrome is usually characterized by loss of limb function 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. 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 bodies. Some patients may have the ability to move certain facial muscles, and most often some or all of the extraocular muscles. Individuals with the syndrome lack coordination between breathing and voice. This prevents them from producing voluntary sounds, though the vocal cords themselves may not be paralysed. Individuals with locked-in syndrome also have intact hearing and subsequent language comprehension. However, these patients might have trouble with voluntary breathing and require assistance due to apnea, ataxia, and hyperpnea. This can be coupled with dizziness and vertigo. Locked-in syndrome patients also have been reported to have involuntary movements such as sucking, chewing, swallowing, yawning, and moaning due to lost pyramidal control of motor systems.

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 essentially the opposite, caused by damage to specific portions of the lower brain and brainstem, with no damage to the upper brain. Injuries to the pons are the most common cause of locked-in syndrome. Possible causes of locked-in syndrome include:

Poisoning cases – More frequently from a krait bite and other neurotoxic venoms, as they cannot usually cross the blood–brain barrier Brainstem stroke Diseases of the circulatory system Drug overdose, such as cocaine or heroin Damage to nerve cells, particularly destruction of the myelin sheath, caused by disease or osmotic demyelination syndrome (formerly designated central pontine myelinolysis) secondary to excessively rapid correction of hyponatremia [>1 mEq/L/h]) A stroke or brain hemorrhage, usually of the basilar artery Traumatic brain injury Result from lesion of the brainstem Trauma Curare poisoning and paralytic shellfish poisoning mimic a total locked-in syndrome by causing paralysis of all voluntarily controlled skeletal muscles. The respiratory muscles are also paralyzed, but the victim can be kept alive by artificial respiration.

Diagnosis Locked-in syndrome can be difficult to diagnose. In a 2002 survey of 44 people with locked-in syndrome, it took almost three months to recognize and diagnose the condition after it had begun. However, it has been reported that it can take upwards of four years to receive a diagnosis. Locked-in syndrome may mimic loss of consciousness in patients, or, in the case that respiratory control is lost, may even resemble death. People are also unable to actuate standard motor responses such as withdrawal from pain; as a result, testing often requires making requests of the patient such as blinking or vertical eye movement. Brain imaging may provide additional indicators of locked-in syndrome, as brain imaging provides clues as to whether or not brain function has been lost. Additionally, an EEG can allow the observation of sleep-wake patterns indicating that the patient is not unconscious but simply unable to move. If no mass or vascular lesion is present on the imaging scan, cerebrospinal fluid examination may be used to reveal an infectious or autoimmune root of the symptoms. Similarly, blood tests can detect fluctuations in sodium concentration, that would be indicative of hyponatremia, as well as glucose levels should be monitored to eliminate the possibility of a hypoglycemic coma.

Similar conditions Akinetic mutism Amyotrophic lateral sclerosis (ALS) Brain death Brain tumor Coma Guillain–Barré syndrome Minimally conscious state Myasthenia gravis Peripheral neuropathy Poliomyelitis Unresponsive wakefulness syndrome Vegetative state

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