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The term “locked-in syndrome” was first introduced in 1966 to describe a state in which a patient is locked inside their body, able to perceive their situation, but with extremely limited ability for interaction. Patients recount that the worst aspect of this syndrome is the anxious desire to move or speak while being unable to do so.
Locked-in syndrome (LIS), also known as cerebromedullospinal disconnection, de-efferented state or pseudocoma, is a rare neurological disorder in which there is complete paralysis of all voluntary movements except movements of the eyes – vertical gaze and eyelid opening. In classical LIS, unlike coma or the vegetative state, individuals are conscious, alert and awake; there is often no impairment of language, memory and intellectual functions; sensation is sometimes also preserved. Due to the loss of voluntary movements, speech is also lost. Communication may be possible through eye movements or blinking.
Incomplete LIS can occur when there are remnants of voluntary movements; total LIS, on the other hand, consists of complete immobility, including loss of eye movements, while maintaining consciousness.
The most common cause for LIS is a lesion in the pons, a part of the brainstem that contains nerve fibers that relay information to other areas of the brain, usually due to brainstem stroke. Another relatively frequent cause is traumatic brain injury, either directly by brainstem lesions or secondary to vascular damage or occlusion. Other, less frequent causes have been reported such as brainstem tumor or brainstem drug toxicity, for example. Another important cause of complete LIS can be observed in end-stage amyotrophic lateral sclerosis (motor neuron disease).
The first person to realize the patient is conscious is often a family member. LIS diagnosis can sometimes take months or even years, since signs of consciousness may not always be easily or immediately perceptible. For a long time, LIS was actually mostly diagnosed retrospectively based on postmortem findings. Unless the physician is aware of the signs and symptoms of LIS, the patient may incorrectly be considered to be in a coma or vegetative state.
Electroencephalographic (EEG) recordings in patients with LIS are usually normal or minimally altered and show reactivity to external stimuli. The presence of a relatively normal reactive EEG rhythm in a patient that appears to be unconscious can allow the diagnosis of LIS. Functional neuroimaging tools, namely PET imaging and functional MRI (fMRI) have shown sensitivity for identification of patients in a minimally conscious state, and may become useful tools to complement bedside examinations.
Individuals with LIS can survive for significant periods of time. Although most deaths occur in the first four months, once a patient has medically stabilized for more than a year, 10 year survival is 83% and 20 year survival is 40%. However, there is no cure or standard treatment available. Typically, the motor rehabilitation is very limited, although some control of fingers and toe movements may be recovered, often allowing a functional use of a digital switch.
Communication can be achieved by a code using eyelid blinks or vertical eye movements. The simplest form can be a yes/no code, such as looking up, indicating “yes” and looking down indicating “no.” A higher level of communication may be achieved through alphabetical systems that allow patients to indicate a letter through eye movement, thereby building sentences. This has even allowed books to be written by LIS patients.
Jean-Dominique Bauby, editor-in-chief of the fashion magazine Elle, had a brainstem stroke in December 1995, at the age of 43. After several weeks in a coma, he emerged into LIS, only able to move his left eyelid. Bauby, wanting to share his experience with the world, dictated a book that he composed mentally. Each passage was dictated letter by letter using a frequency-ordered alphabet with Bauby choosing letters by blinking. His book The Diving Bell and the Butterfly was published two days before his death in March 1997 and became a best-seller. The book was later adapted into a film of the same name, released in 2007.
Julia Tavalaro fell into a coma after a hemorrhage in 1966, at the age of 32. After seven months, she woke up in a chronic care facility where she was regarded as a “vegetable”. It was only after several years that her family noticed a smile as a reaction to a dirty joke. She initially communicated using a letter board, but later used a communication device to write poetry, and managed to cheek-control her wheelchair. She died in 2003 at the age of 68.
Philippe Vigand fell into a coma in 1990 due to a vertebral artery dissection, also at the age of 32. He remained in a coma for two months and was later treated as a “vegetable”. His wife eventually noticed him blinking in response to her questions, but was unable to convince the treating physicians of his conscious state. His speech therapist was able to diagnose LIS when Vigand grinned after an insult from the therapist, whose finger was bitten by Vigand while testing his gag reflex. He then asked how much two plus two was and Vigand blinked four times confirming his cognitive capacities. He initially also communicated using a letter board, but later used an infrared camera attached to a computer.
Meanwhile, technology has contributed significantly to patients’ communication abilities. Instruments such as infra-red eye movement sensors coupled to virtual keyboards allow the use of word processors which in turn can be coupled to a text-to-speech synthesizer. These can also let the LIS patient control his environment, access the Internet and use e-mail, for example. Brain-computer interfaces (BCI) are also tools that allow LIS patients to control devices directly, but by using EEG signals to control computers. An example is the use of BCI involving visual presentation of letters associated with selection through EEG and a statistical language model. However, these tools are mostly still being tested or are too expensive for generalized use.
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