Minimally conscious state

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Minimally Conscious State
Brain scans of various disorders of consciousness, including minimally conscious state

A minimally conscious state or MCS is a

pediatric), or between 112,000 and 280,000 in the US by year 2000.[2]

Pathophysiology

Neuroimaging

Because minimally conscious state is a relatively new criterion for diagnosis, there are very few functional imaging studies of patients with this condition. Preliminary data has shown that overall cerebral metabolism is less than in those with conscious awareness (20–40% of normal

prefrontal cortices in MCS than vegetative states. These findings encourage treatments based on neuromodulatory and cognitive revalidation therapeutic strategies for patients with MCS.[4]

Resting overall cerebral metabolism of various brain states.[4]
Arousal levels of various brain states.[4]

One study used

axons to occur in the intact areas of the cortex, which may explain some of the greater recovery rates in minimally conscious state patients. The axonal regrowth has been correlated with functional motor recovery. The regrowth and rerouting of the axons may explain some of the changes to brain structure. These findings support the efforts to prospectively and longitudinally characterize neuroplasticity in both brain structure and function following severe injuries. Utilizing DTI and other neuroimaging techniques may further shed light on the debates on long-distance cortical rewiring and may lead to better rehabilitation strategies.[5]

Some areas of the brain that are correlated with the subjective experience of pain were activated in MCS patients when

analgesia in patients with MCS.[6]

Residual language function

A functional magnetic resonance imaging (fMRI) study found that minimally conscious state patients showed activation in auditory networks when they heard narratives that had personally meaningful content that were read forwards by a familiar voice. These activations were not seen when the narratives were read backwards.[7]

Another study compared patients in vegetative state and minimally conscious state in their ability to recognize language. They found that some patients in minimally conscious state demonstrated some evidence of preserved speech processing. There was more activation in response to sentences compared to white noise.[8]

Diagnostic

Medical definition

Minimally conscious state (MCS) is defined as a condition of severely altered consciousness in which minimal but definite behavioral evidence of self or environmental awareness is demonstrated.[1]

Diagnosis

Although MCS patients are able to demonstrate cognitively mediated behaviors, they occur inconsistently. They are, however, reproducible or can be sustained long enough to be differentiated from reflexive behavior. Because of this inconsistency, extended assessment may be required to determine if a simple response (e.g. a finger movement or a blink) occurred because of a specific environmental event (e.g. a command to move the finger or to blink) or was merely a coincidental behavior.[1] Distinguishing between VS and MCS is often difficult because the diagnosis is dependent on observation of behavior that show self or environmental awareness and because those behavioral responses are markedly reduced. One of the more common diagnostic errors involving disorders of consciousness is mistaking MCS for VS which may lead to serious repercussions related to clinical management.[9]

Giacino et al. have suggested demonstration of the following behaviors in order to make the diagnosis of MCS.

  • Following simple commands such as following movements with their eyes or moving a finger when asked.[10]
  • Gestural or verbal yes/no responses (regardless of accuracy).
  • Intelligible verbalization.
  • Purposeful behavior such as those that are contingent due to appropriate environmental stimuli and are not reflexive. Some examples of purposeful behavior include:
    • appropriate smiling or crying in response to the linguistic or visual content of emotional but not to neutral topics or stimuli.
    • vocalizations or gestures that occur in direct response to the linguistic content of questions.
    • reaching for objects that demonstrates a clear relationship between object location and direction of reach.
    • touching or holding objects in a manner that accommodates the size and shape of the object.
    • pursuit eye movement or sustained fixation that occurs in direct response to moving or salient stimuli.[1]

Treatment

There is currently no definitive evidence that support altering the course of the recovery of minimally conscious state. There are currently multiple

clinical trials underway investigating potential treatments.[11]
In one case study, stimulation of thalamus using
focus.[12]

In another case study of a 50-year-old woman who had symptoms consistent with MCS, administration of

GABA-mediated mechanism and the inhibition was modified by zolpidem which is a GABA agonist. The fact that zolpidem is a sedative drug that induces sleep in normal people but causes arousal in a MCS patient is paradoxical. The mechanisms to why this effect occurs is not entirely clear.[13]

There is recent evidence that transcranial direct current stimulation (tDCS), a technique that supplies a small electric current in the brain with non-invasive electrodes, may improve the clinical state of patients with MCS. In one study with 10 patients with disorders of consciousness (7 in VS, 3 in MCS), tDCS was applied for 20 minutes every day for 10 days, and showed clinical improvement in all 3 patients who were in MCS, but not in those with VS. These results remained at 12-month follow-up. Two of the patients in MCS that had their brain insult less than 12 months recovered consciousness in the following months. One of these patients received a second round of tDCS treatment 4 months after his initial treatment, and showed further recovery and emerged into consciousness, with no change of clinical status between the two treatments.[14]

Prognosis

One of the defining characteristics of minimally conscious state is the more continuous improvement and significantly more favorable outcomes post injury when compared with vegetative state. One study looked at 100 patients with severe brain injury. At the beginning of the study, all the patients were unable to follow commands consistently or communicate reliably. These patients were diagnosed with either MCS or vegetative state based on performance on the JFK

tumor, hydrocephalus, infection). The patients were assessed multiple times over a period of 12 months post injury using the Disability Rating Scale (DRS) which ranges from a score of 30=dead to 0=no disabilities. The results show that the DRS scores for the MCS subgroups showed the most improvement and predicted the most favorable outcomes 12 months post injury. Amongst those diagnosed with MCS, DRS scores were significantly lower for those with non-traumatic brain injuries in comparison to the vegetative state patients with traumatic brain injury. DRS scores were also significantly lower for the MCS non-traumatic brain injury group compared to the MCS traumatic brain injury group. Pairwise comparisons showed that DRS scores were significantly higher for those that suffered from non-traumatic brain injuries than those with traumatic brain injuries. For the patients in vegetative states there were no significant differences between patients with non-traumatic brain injury and those with traumatic brain injuries. Out of the 100 patients studied, 3 patients fully recovered (had a DRS score of 0). These 3 patients were diagnosed with MCS and had suffered from traumatic brain injuries.[9]

In summary, those with minimally conscious state and non-traumatic brain injuries will not progress as well as those with traumatic brain injuries while those in vegetative states have an all around lower to minimal chance of recovery.

Because of the major differences in prognosis described in this study, this makes it crucial that MCS be diagnosed correctly. Incorrectly diagnosing MCS as vegetative state may lead to serious repercussions related to clinical management.

History

Prior to the mid-1990s, there was a lack of operational definitions available to clinicians and researchers to guide the differential diagnosis among

Persistent Vegetative State
" was published by the American Academy of Neurology (AAN) in 1994. In 1995, "Recommendations for Use of Uniform Nomenclature Pertinent to Patients With Severe Alterations in Consciousness" was published by the American Congress of Rehabilitation Medicine (ACRM). In 1996 the "International Working Party on the Management of the Vegetative State: Summary Report" was published by a group of international delegates from neurology, rehabilitation, neurosurgery, and neuropsychology. However, because the diagnostic criteria were published independently from one another, the final recommendations differed greatly from one another. The Aspen Neurobehavioral Work-group was convened to explore the underlying causes of these disparities. In the end, the Aspen Work-group provided a consensus statement regarding definitions and diagnostic criteria disorder of consciousness which include the vegetative state (VS) and the minimally conscious state (MCS).[15]

Ethical issues

One of the major ethical concerns involving patients with severe brain damage is their inability to communicate. By definition, patients who are unconscious or are minimally conscious are incapable of giving informed consent which is required for participation in clinical research. Typically, written approval is obtained from family members or legal representatives. The inability to receive informed consent has led to much research being refused grants, ethics committee approval, or research publication. This puts patients in these conditions at risk of being denied therapy that may be life-saving.[4]

The right to die

The

Terri Schiavo who was diagnosed with persistent vegetative state. In the case of minimally conscious state patients, they are neither permanently unconscious nor are they necessarily hopelessly damaged. Thus, these patients warrant additional evaluation.[16] On one hand, some argue that entertaining the possibility of intervention in some patients may erode the "right to die" moral obligation. Conversely, there is also fear that people may associate attitudes with higher-functioning people in minimally conscious state with people in persistent vegetative state, thus minimizing the value of their lives.[17]

Regulating therapeutic nihilism

Currently, risk aversion dominates the ethical landscape when research involves those with impaired decision-making abilities.[16] Fears of therapeutic adventurism has led to a disproportionate view about the under-appreciation of potential benefits and an overstatement of risks[clarification needed]. Thus, recognizing this distortion is important in order to calculate the right balance between protecting vulnerable populations that cannot provide autonomous consent and potentially restorative clinical trials.[16]

Notable examples

  • Jackie Wilson (June 9, 1934 – January 21, 1984), American soul and rock and roll singer who fell into a coma after collapsing on stage, soon recovered conscious but then quickly regressed to a minimally conscious state for the rest of his life.
  • Jan Grzebski (1942–2008), a Polish railroad worker who fell into a minimally conscious state in 1988 and woke up four years later, but didn't fully recover until 2007.
  • Chi Cheng (1970-2013), an American musician best known as the original bassist for the band Deftones who was involved in a serious automobile accident in 2008 that left him in a minimally conscious state for the rest of his life.
  • Terry Wallis (1964-2022). This American man was in a coma for nearly a year after a truck accident, then a minimally conscious state for 19 years.
  • Martin Pistorius (born 1975), a South African man who, because of a mystery illness, spent three years in a vegetative state, four years in a minimally conscious state, and five years unable to move anything other than his eyes (locked-in syndrome). In 1999, he fully awakened, and has since recovered to the point that he was able to become a web designer, developer, and author. In 2011, he wrote a book called Ghost Boy, in which he describes his many years of being comatose.

References

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  11. ^ NIH. "Clinicaltrials.gov".
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External links

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