Introduction

Locked-in syndrome is one of the most frequently misdiagnosed neurological conditions. It’s defined as a state of mental clarity yet apparent silence. Neuroimaging provides critical insight into brain function, helping doctors differentiate LIS from a coma, growing states, or brain death.¹ This guide explains the main imaging tools, including MRI, CT, and functional techniques, that help clinicians identify LIS and support patients trapped inside unresponsive bodies.

What is locked-in syndrome (LiS)?

Locked-in syndrome (LiS) is a rare neurological disorder in which a person is fully conscious and alert but unable to move or communicate because of paralysis. Typically, people with LiS only retain the ability to blink and use their vertical eye muscles, which are vital for communication.²

LiS can be caused by stroke, trauma, tumours, or other neurological conditions, but is most frequently brought on by damage to particular parts of the brainstem, especially the pons. LiS is classified based on the level of impairment:²

1. Classical LiS: Defined as paralysis with unaltered vertical eye movement and complete consciousness
2. LiS incomplete: There might still be voluntary movements
3. Total LiS: No eye or other voluntary movements at all
4. Locked-in plus syndrome: Involves reduced consciousness in addition to the classic features of locked-in syndrome, further complicating the diagnosis

It's critical to get an accurate diagnosis because disorders like akinetic mutism and cognitive motor dissociation (CMD) might look alike.²

Early multidisciplinary intervention is the mainstay of treatment, which also includes psychological support, intensive rehabilitation, and the development of communication techniques. Developing communication is one of the main objectives of therapy.²

Though many patients report a surprisingly great quality of life, caregivers and medical professionals frequently have a negative outlook on life with LiS. The significance of upholding patient autonomy, encouraging dignity, and reconsidering cultural presumptions regarding severe impairment is underscored by this disparity.²

To enable people with LiS to lead fulfilling lives, it is imperative to increase awareness, enhance diagnosis, and develop assistive technologies. The necessity for patient-centred care and additional research is critical.²

The significance of neuroimaging in LiS

Neuroimaging is crucial because it allows us to see the anatomy and function of the brain without undergoing surgery. These tools allow us to understand how different brain regions interact to regulate thinking, memory, focus, language, emotion and even decision making. fMRI, PET, EEG, and MEG are common neuroimaging techniques utilised in the study of the brain. Each of these techniques offers different levels of information regarding the location and timing of brain activity.³

Locked-in syndrome (LiS) is often difficult to differentiate from other consciousness disorders with physical examinations alone. Neuroimaging provides critical visual evidence that can help differentiate LiS from conditions such as coma or brain death. The EEG is particularly useful in this process as it assesses the activity patterns of the brain.⁴ Accurate diagnosis is essential not only for prognosis but also to guide appropriate rehabilitation strategies and communication techniques tailored to the patient's residual capabilities.⁵ By examining electrical and metabolic activity, clinicians can determine whether cortical function is intact.⁶

LiS diagnosis using neuroimaging

The diagnosis of locked-in syndrome (LiS) is mostly dependent on neuroimaging. This is because physical examinations are frequently unable to differentiate from other consciousness problems. Magnetic resonance imaging (MRI) is the gold standard among imaging modalities, whereas computed tomography (CT) and functional imaging techniques perform complementary roles.

MRI: the gold standard

MRI, particularly T2-weighted and diffusion-weighted imaging (DWI), is the most efficient tool for identifying the hallmark feature of LIS: bilateral lesions in the ventral pons with sparing of the tegmentum, thereby preserving awareness pathways. Since DWI can identify ischaemia alterations minutes after a stroke occurs, it is very useful for enabling early diagnosis and appropriate treatment. Additionally, MRI provides high-resolution soft tissue pictures without ionising radiation, which makes it perfect for thorough evaluation and continuous observation.⁷

CT: rapid initial assessment

CT scans are readily accessible and offer a quick, non-invasive test that is helpful during emergencies. They are useful in ruling out massive infarcts and haemorrhages. However, CT scans have a low sensitivity for detecting small brainstem lesions, particularly in the early stages of LIS. For an accurate diagnosis, an MRI is usually necessary. Therefore, it is known as the gold standard, even though CT scans can direct treatment right away.⁸

Functional imaging techniques

fMRI (functional MRI)

For individuals with consciousness disorders, including the comatose state, functional magnetic resonance imaging (fMRI) has become a potent method for identifying latent awareness. When asked to do mental imagery tasks, such as playing tennis or navigating her home, a patient who had been clinically labelled as comatose showed brain activation patterns that were identical to those of healthy people. This breakthrough demonstrated that, despite the lack of physical responsiveness, cognitive function was retained since she was able to comprehend instructions and purposefully react with just her brain activity. 

This approach has direct implications for conditions like locked-in syndrome (LiS), where patients are completely cognisant but unable to move or speak. When normal clinical tests are unable to detect conscious awareness in LIS patients, fMRI provides a non-invasive way to identify preserved cognition. It may even pave the way for basic communication by interpreting intentional changes in brain activity.⁹

PET (positron emission tomography)

PET scans, which use 18F-FDG, can give clinicians more insight into the brain activity of patients who seem to be unconscious. In one study, PET proved to be very successful in detecting patients who were in a minimally conscious condition, even when bedside examinations failed to detect it. Brain activity on PET scans indicated some degree of consciousness in about one-third of individuals who appeared unresponsive on clinical assessments. Later, a large number of these individuals regained consciousness. For individuals with locked-in syndrome, who are frequently misdiagnosed because of their lack of movement or conversation, this indicates that PET scans can help identify concealed signals of consciousness.¹⁰

Real-world challenges and care in LiS

Locked-in syndrome (LiS) is typically brought on by a stroke, haemorrhage, or damage to the brainstem, especially the ventral pons. Although they can frequently communicate with their eyes, people with LiS are fully aware but unable to move or speak. Many survive for years, and others recover enough to go back to their families' homes despite significant physical limitations. A higher quality of life can be achieved with early access to specialist therapy. 

While some individuals retain complete mental capacities, others may experience impairments in cognitive functions such as memory and attention, particularly in cases of stress. PET scans can assist doctors in distinguishing LiS from illnesses such as the vegetative state by demonstrating that brain activity in LiS is near normal, as opposed to the substantially diminished activity seen in vegetative patients. This emphasises how crucial it is to diagnose and treat LiS patients appropriately.¹¹

Challenges and future directions

One of the main obstacles to using neuroimaging for locked-in syndrome is the high expense and restricted availability of technologies such as fMRI and PET, which are usually only available in specialist tertiary institutes. The accuracy of fMRI or DTI scans can also be compromised by artefacts caused by even the slightest patient movements, as these imaging techniques are extremely sensitive to motion. Another persistent problem is that different institutions do not have standardised imaging techniques, which makes it challenging to replicate and compare data in various clinical situations.¹²

Summary

Locked-in syndrome (LiS) is a rare neurological disorder in which individuals are fully aware but are unable to move or talk, with the exception of restricted eye movement used for communication. It is usually caused by injury to the brain, known as the ventral pons. As LiS is usually confused with coma or vegetative states, it can be difficult to diagnose. The accuracy of the diagnosis relies on neuroimaging techniques such as MRI and CT. MRI is the gold standard because of its high resolution and early detection of brainstem lesions. When a patient is unresponsive, functional imaging techniques like fMRI and PET scans can reveal underlying consciousness, improving the diagnosis and communication opportunities. Despite these developments, there are still issues present, such as high costs, restricted access to advanced imaging, motion artefacts and a lack of established procedures. Improving patient outcomes and quality of life requires early specialised treatment and rehabilitation.

FAQs

What causes locked-in syndrome?

It’s typically caused by injury to the ventral region of the brainstem, specifically the pons. Traumatic brain injury (TBI), bleeding, tumours and strokes can cause such damage. The damage impairs motor pathways, resulting in paralysis without affecting consciousness or eye movements.¹³

How is LiS diagnosed?

It primarily relies on clinical observation of intact vertical eye movements and retained consciousness with the condition. Neuroimaging techniques, such as MRI, are used for diagnosis. Functional imaging techniques such as fMRI and PET scans can assist in differentiating LiS from other disorders by detecting the residual brain activity that indicates awareness.⁹