Functional locked-in syndrome as recovery phase of vegetative state

Recently, functional neuroimaging and advanced electrophysiology studies showed residual cortical processing in the absence of behavioural signs of consciousness in some non-communicative, severely brain-damaged patients.

The term ‘functional locked-in syndrome’ has been proposed to describe patients with a dissociation between extreme motor dysfunction and preserved higher cortical functions identified only by functional imaging techniques [1]. Nevertheless, patients clinically diagnosed in the vegetative state who are able to perform mental imagery tasks [2] are still considered in the vegetative state with preserved islands of consciousness, not as having functional locked-in syndrome.

Although patients with functional locked-in syndrome who are misdiagnosed as unaware persons are considered rare [3], the syndrome is not uncommon during recovery from a vegetative state.

Indeed, locked-in syndrome may present with initial attempts to engage in eye-coded communication after a vegetative or minimally conscious state [4].

In the latter case, the low sensitivity of functional neuroimaging with mental imagery tasks may be due to concomitant cognitive deficits, which are also generally present after prolonged disorders of consciousness (DOC) in patients who have already emerged from a minimally conscious state.

More recently, Cruse at al. [5] demonstrated that it is also possible to detect the hidden awareness of patients in the vegetative state using an electroencephalography (EEG) technique.

The scientific community should clearly indicate that patients who are behaviourally in a vegetative state in whom residual cortical processing has been demonstrated by means of fMRI or neurophysiology are not vegetative/unresponsive/unaware. In fact, these persons with wilful communication ability have functional locked-in syndrome, clinically misdiagnosed as a vegetative state.

Although the presence of islands of residual consciousness in individuals with VS should challenge the clinical diagnosis of vegetative state, the lack of residual cortical processing should not exclude the presence of islands of consciousness. Vigilance fluctuations and severe cognitive deficits may, in fact, cover any evidence of residual cortical activation [5].

Thus, functional neuroimaging and electrophysiology can be used in doubtful cases of DOC to rule out tests for the diagnosis of vegetative state.

Indeed, patients with residual cognitive functions who are able to perform complex mental imagery tasks or show intentional communication ability should be diagnosed with functional locked-in syndrome and not vegetative state with hidden consciousness.

Declaration of interest

The authors report no conflicts of interest and no financial support. The authors alone are responsible for the content and writing of the paper.

Acknowledgements

We would like to thank Claire Montagna for her revision of the English.