Minimally conscious state
Minimally Conscious State (MCS) is a specific disorder of consciousness characterized by inconsistent but definitive signs of awareness, distinguishing it from conditions like coma and vegetative state (VS). In MCS, individuals exhibit near-normal wakefulness and can respond to commands, gestures, or environmental stimuli, though these responses may vary in consistency. Diagnosis relies on behavioral evidence such as following simple commands or demonstrating purposeful behaviors, rather than reflexive actions. While many individuals may transition out of MCS in less than three months, some may remain in this state indefinitely.
There are currently no standardized treatments for MCS; however, rehabilitation typically focuses on preventing medical complications and managing environmental stimulation. Amantadine hydrochloride is the only medication proven to facilitate recovery, though other drugs have shown potential in individual cases. Care for MCS patients often requires a multidisciplinary approach, involving neurologists, rehabilitation specialists, and therapists to address the diverse needs of patients. Research continues to evolve in understanding MCS, aiming to enhance detection methods and improve patient outcomes, as those who achieve MCS early after injury often have better prognoses compared to those in VS.
Minimally conscious state
Disease/Disorder
Anatomy or system affected: Central nervous system
Definition: A condition of severely altered consciousness in which minimal, but definite, behavioral evidence of self or environmental awareness is demonstrated.
Key terms:
arousal: the degree of wakefulness
awareness: the perception of one's self and the environment
brain connectivity: a pattern of structural and functional interactions within and between cortical and subcortical structures
disorder of consciousness (DoC): a medical condition caused by acquired brain injury (traumatic or nontraumatic) and characterized by impairments in arousal and awareness of self and environment
Causes and Symptoms
Minimally conscious state (MCS) is one of several disorder of consciousness (DoC) syndromes associated with alteration in arousal, impaired self and environmental awareness, and disruption of brain connectivity necessary for supporting conscious awareness. The most severe disorder, coma, is characterized by complete loss of arousal and no behavioral signs of awareness. In the vegetative state (VS), the arousal system recovers and sleep-wake cycles return, but behavioral signs of awareness remain absent. In coma and VS, subcortical functions are partially preserved, but interactions between cortical and subcortical structures are severely diminished or completely lost. Conversely, MCS is characterized by near-normal to normal wakefulness and at least one definitive behavioral sign of awareness. The hallmark feature of MCS is inconsistency in volitional responses. The transition from coma and VS to MCS is coupled to the recovery of cortico-cortical and cortico-subcortical connectivity.
The diagnostic criteria for MCS are based on reproducible or sustained behavioral evidence of one or more of the following:
- • simple command-following
- • gestural or verbal yes/no responses (regardless of accuracy)
- • intelligible verbalization
- • purposeful behavior, including movements or affective behaviors that occur in contingent relation to relevant environmental stimuli and are not due to reflexive activity (e.g., visually tracking a moving object)
While most people progress through MCS in less than three months, others may remain in MCS permanently. Clear evidence of either of the following behaviors mark emergence from MCS:
- • functional interactive communication (i.e., consistent and accurate yes-no responses to personal or situational orientation questions)
OR
- • functional object use (i.e., appropriate demonstration of the use of at least two common objects)
Observational assessment of behavior remains the “gold standard” for differential diagnosis among DoC. This method may lead to misdiagnosis as the evaluation of level of consciousness may be confounded by fluctuations in arousal level, sensory deficits, motor limitations, cognitive dysfunction, language impairment, diminished behavioral drive, and other factors. Use of standardized assessments, such as the Coma Recovery Scale-Revised (CRS-R), has been shown to decrease the rate of misdiagnosis.
Treatment and Therapy
Currently, there are no standards of care for treatment of persons in MCS. Prevention of common medical complications associated with severe brain injury, avoidance of prolonged immobilization, and management of environmental stimulation are typically the primary goals of rehabilitation. Common complications include, but are not limited to, spasticity, autonomic dysfunction, pneumonia, urinary tract infection, and sleep disturbance.
Pharmacologic agents are often used to promote arousal, increase behavioral initiation, decrease agitation, and regulate sleep in patients in MCS. However, amantadine hydrochloride is the only therapeutic agent shown to be effective in increasing the rate of recovery in patients in traumatic VS and MCS. There is also growing interest in the sleep medication zolpidem and the anti-anxiety drug midazolam, as a few case studies have reported dramatic increases in arousal, speech, and volitional behavior within 30 minutes of administration. A broad range of other treatment interventions, including other drug therapies, invasive and noninvasive brain stimulation procedures and cognitive rehabilitation, have been used to promote recovery, although their effectiveness remains largely unproven.
Science and Profession
While there is no consensus on the best method of treatment for MCS, a collaborative, multidisciplinary approach that engages the expertise of multiple clinical specialties is essential for effective management of the wide-ranging and long-term needs of this population.
During the acute hospitalization, stabilization, and management of the primary and secondary effects of the injury necessitate the collective expertise of neurologists, neurosurgeons, and physiatrists. Once the critical medical issues have been stabilized, the patient may be evaluated and treated by a rehabilitation team consisting of physical and occupational therapists, speech language pathologists, and clinical neuropsychologists. When implementing a multidisciplinary approach, clinicians across specialties collaborate on common assessment strategies and treatment goals.
Perspective and Prospects
MCS was originally referred to as the minimally responsive state; however, this term was abandoned to avoid conflating reflexive and automatic behavioral responses with those that are volitional. The diagnosis of MCS was formally established by the Aspen Neurobehavioral Workgroup in 2002. A major impetus for differentiating patients in MCS from those in VS was a growing body of research showing that the outcome from MCS was significantly more favorable relative to VS. Many subsequent studies have validated these findings and suggest that people who reach MCS within the first three months of injury have a lower mortality rate and are more likely to have a lower degree of functional disability by 12 months postinjury. Current efforts are underway to improve detection of MCS early after injury, better define the upper boundary of MCS, and identify factors that influence outcome.
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