What Is Locked-In Syndrome?

Locked-in syndrome (LIS) is a rare neurological disorder characterized by complete paralysis of all voluntary muscle movements except those involved in moving the eyes or eyelids. People with LIS have normal levels of consciousness and situational awareness but can't communicate verbally. They can communicate using eye movements, blinking, or with the help of assistive technologies.

This article discusses the cause of locked-in syndrome, how you know if someone has locked-in syndrome, types of LIS, its symptoms, diagnosis, treatment options, and survival rates.

Brief History of Locked-In Syndrome

In 1966, locked-in syndrome was first described by two U.S. neurologists, Fred Plum and Jerome Posner, who differentiated between various types of coma in their landmark book, The Diagnosis of Stupor and Coma. Plum and Posner observed that some patients who may appear to be comatose are actually conscious and feel trapped in their bodies, which led to the term "locked-in syndrome."

Although these seemingly comatose patients were conscious, being “locked in” meant that they couldn’t move their body parts, speak, or make facial expressions. However, despite being paralyzed, most of them could make vertical eye movements and were able to blink their eyelids.

Locked-in syndrome is also called “pseudocoma” because patients often appear to be in a coma, but are actually conscious and self-aware. Another clinical term used to describe locked-in syndrome is “cerebromedullospinal disconnection,” which is used to describe damage in the brain stem region (the pons) that connects upper portions of the brain to the spinal cord.

Types of Locked-In Syndrome

In the late 1970s, different types of locked-in syndrome were broken down into three categories as follows:

1. Classical: Classical locked-in syndrome is characterized by complete paralysis (quadriplegia) and an inability to speak or communicate verbally. People with classic form LIS don't have any mobility in their extremities and can’t make facial expressions but can move their eyes vertically and blink.
2. Partial: All the same symptoms characterize the partial form of locked-in syndrome as the classical form, but the patient has some motor function.
3. Total immobility: Characterized by complete paralysis of the entire body, including an inability to make vertical eye movements or blink, this form of LIS is very difficult to diagnose because patients seem comatose and can’t communicate with their eyes.
   

Notably, if the brain activity of a locked-in patient with total immobility is measured using an electroencephalogram (EEG), the readings will typically show that the unresponsive patient isn't in a persistent vegetative state (PVS; or post-coma unresponsiveness) and hasn't experienced brain death but is in a pseudocoma.

Locked-In Syndrome Symptoms

Locked-in syndrome can have a variety of symptoms. The categorization of the three forms of LIS provides a basic framework for gauging the condition's severity based on a patient's symptoms.

To varying degrees, the following symptoms are characteristic of locked-in syndrome:

• Paralysis of limbs and torso
• Inability to move muscles (except eyes/eyelids) voluntarily
• Vertical eye movements often retained
• Blinking ability often retained
• Retention of consciousness
• Retention of executive function (aspects of thinking like memory, planning, etc.)
• Retention of hearing and language comprehension
• Poor muscle control (ataxia)
• Difficulty with voluntary breathing
• Difficulty swallowing (dysphagia)
  
• Inability to communicate verbally (anarthria/dysarthria)
  
  

Causes

Locked-in syndrome is typically caused by damage to the brain stem’s pons. This bridge-like brain stem region has neural pathways that connect the body to the brain via the spinal cord.

When the pons is damaged, it cuts off signals from upper brain areas responsible for controlling voluntary movement to lower brain regions such as the cerebellum, which coordinates motor functions. If the pons can't communicate between brain areas that control movement and the spinal cord, it causes paralysis and the inability to move body muscles.

LIS-inducing pons damage can be caused by many things, such as:

• Brain stem stroke
• Brain bleed (hemorrhage)
• Brain tumor
• Brain lesion
• Blood clot (thrombosis)
• Neurodegenerative diseases
• Amyotrophic lateral sclerosis (ALS)
• Demyelinating diseases (loss of myelin)
• Traumatic brain injury (TBI)
• Poisoning (in cases of snake bite with neurotoxic venom)
  

Diagnosis

Locked-in syndrome diagnosis is typically made using neurological exams and diagnostic tools that rule out other conditions. For example, an EEG can be used to measure brain activity and assess whether someone who appears to be comatose or in a vegetative state is actually in a pseudocoma.

Brain imaging technologies such as magnetic resonance imaging (MRI), can show if there’s damage to the pons. Magnetic resonance angiography (MRA) is a diagnostic tool that shows blood flow in the brain and can be used to see if brain stem arteries are blocked or damaged in someone with LIS symptoms.

Of the three types of locked-in syndrome, the severest form (total immobility) is the most difficult to diagnose because patients can’t communicate with their eyes. LIS patients with total immobility don’t appear conscious or alert to onlookers. However, if their brain activity is measured using EEG, it will typically show normal levels of consciousness.

Treatment

There isn’t a cure or standard course of treatment for locked-in syndrome. Treatment options will vary depending on the root cause of a patient’s LIS symptoms.

Functional neuromuscular electrical stimulation is a therapy that activates paralyzed muscles and may facilitate some voluntary movement in people with paralysis. However, most patients with LIS will have trouble carrying out daily activities due to highly impaired motor functions.

Assistive technologies like eye tracker devices can help patients with locked-in syndrome communicate using vertical eye movements and shifting their gaze. Advances in brain-computer interface (BCI) technology show promise for allowing patients with locked-in syndrome to communicate in sentences using just their thoughts.

Prognosis

The prognosis for most patients with locked-in syndrome isn't good. On average, most patients with locked-in syndrome remain locked in. It's rare for adults with LIS to regain motor functions.

About 35% of children with LIS regain some voluntary movement. Almost 90% of deaths occur within the first four months of a patient becoming locked in. If someone with LIS is medically stabilized and survives the first year, a 2019 cohort study found that the five-year survival rate among those who underwent rehabilitation can reach 86%.

A 2015 study of patients with locked-in syndrome found that preserving communication with others is key to stabilizing the quality of life and maintaining psychological well-being. A 2011 survey on self-assessed well-being among a cohort of 65 chronic locked-in syndrome patients found that the majority (72%) considered themselves happy, while 18 patients (28%) professed unhappiness.

Summary

Locked-in syndrome is a paralyzing disorder typically caused by damage to the pons region of the brain stem, which connects the upper portions of the brain to the spinal cord. When the pons is damaged, it causes paralysis because the brain can't send signals to the body that initiate voluntary muscle movements.

People with locked-in syndrome can't move their bodies or speak, but they can usually move their eyes and blink. Eye tracker technology and brain-computer interfaces make it possible for people with locked-in syndrome to communicate, significantly improving their quality of life.