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.^[3] This is due to quadriplegia and bulbar palsy. The person is conscious and sufficiently intact cognitively to communicate with eye movements.^[4] 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.^[5][6]

Locked-in syndrome can be separated into subcategories based on symptom severity.^[7] 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 as 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.