ISCHEMIC STROKE / ETIOLOGY

Specific consciousness disorders

David Goldemund M.D.
Updated on 25/11/2023, published on 20/11/2023

  • components of consciousness, namely arousal (vigilance), awareness, and attention, may be affected differently depending on the type and distribution of the underlying brain lesion
  • disturbance of arousal affects wakefulness and awareness and leads to somnolence, stupor (sopor), or coma (quantitative consciousness disorders). Reduced arousal is caused by  lesions of the ascending reticular activating system (ARAS), which is situated in the upper brainstem and the paramedian diencephalon, and its connections to the cerebral cortex
  • qualitative consciousness disorders are characterized by altered awareness and attention (such as delirium, confusion, unresponsive wakefulness syndrome, minimally conscious state, and psychogenic unresponsiveness)
  • qualitative and quantitative disorders may coexist
  • this chapter describes less frequent conditions that may occur as a consequence of brain damage (stroke, TBI, etc.) when the initial coma partially resolves (arousal is restored)
    • delirium and quantitative consciousness disorders and their classification are discussed elsewhere
  • the chronic vegetative state describes a condition characterized by a total mental loss (awareness and attention) while vegetative functions and arousal (wakefulness) are preserved (wakeful unconscious state or unresponsive wakefulness syndrome)
  • dysfunction results from either toxic-metabolic or extensive structural lesions of the cerebral cortex, where the limbic and mesial frontal areas play a dominant role
  • to differentiate between toxic-metabolic and structural brain diseases, it is essential to examine motor reactions, ocular movements, and pupillary reflexes
  • in DDx of consciousness disorders, the possibility of locked-in syndrome must be considered

Coma

  • coma = a state of prolonged unarousable unconsciousness characterized by the absence of signs of both wakefulness and awareness. It features a total absence of reaction to external stimuli (auditory, visual, and noxious)
    • patient in a coma is unable to perform spontaneous movements, display any form of voluntary behavior, or produce  vocalizations
  • loss of consciousness due to acute brain injury may result from:
    • direct neural damage (traumatic brain injury)
    • insufficient cerebral blood perfusion (stroke, cardiac arrest)
    • hypoxia, intoxication, or metabolic disorder
    • sedatives administered to the patient by healthcare staff
  • a minimum duration of one hour is typically used to distinguish coma from shorter episodes of unconsciousness, such as syncope or seizure
  • when coma is not related to the administration of sedative agents, it usually indicates impairment in brainstem structures or extensive bilateral cortical lesions

Unresponsive wakefulness syndrome (UWS)

  • comatose patients may recover signs of wakefulness, such as eye-opening or vegetative nervous system activities, while still lacking clinical signs of awareness
  • this condition of preserved arousal without awareness has been known by various terms (coma vigile and apallic syndrome are now outdated, but the vegetative state (VS) is still used)
  • the term “persistent vegetative state” defines patients who remain in VS for over one month, while the “permanent vegetative state” was traditionally used for patients in VS for more than 3months (in the US) or 6 months (in the UK) following non-traumatic injuries, and for over 12 months in cases of traumatic injuries
  • recent guidelines recommend replacing these terms with “chronic vegetative state” or “unresponsive wakefulness syndrome (UWS)“
  • functional MRI (fMRI) may help detect partial awareness, which has prognostic implications (increased likelihood of evolution to a minimally conscious state) )   (Marino, 2017)
Definition
  • the affected individual exhibits signs of wakefulness yet remains inert to stimuli from the surrounding environment, manifesting as akinesia and mutism
Pathophysiology
  • UWS typically results from severe brain damage, leading to a disconnection between the cerebral cortex and the thalamus (altered connection between the ascending mesothalamic reticular system and the anterior cingulate region and neocortical structures)
    • brain damage can be either diffuse or localized
    • the reticular activating system remains functional, enabling wakefulness
  • pathological lesions leading to UWS:
    • bithalamic paramedian lesions involving the reticular formation and extending into the diencephalic-mesencephalic boundary; most commonly caused by medial bithalamic infarcts
    • bifrontal lesions in these locations:
      • bifrontal cingulate lesions affecting the limbic cortex in the anterior parts of the cingulate gyrus (territory of the anterior cerebral arteries)
      • bifrontal precentral subcortical lesions interrupting thalamofrontal and reticulofrontal projections to the anterior limbic cortex
Clinical presentation
  • “thoughtless” wakefulness
    • states of vigilance that may alternate with deep somnolence and, at times, episodes of agitation
  • the patient is mute, unaware of surroundings, does not respond to external stimuli (tactile, noxious, visual, or auditory), and may have preserved a sleep-wake cycle
    • in some cases, escape reactions in limbs can be provoked by repeated painful stimulation
    • during episodes of agitation, spontaneous limb movements and screaming may occur
  • additional signs and symptoms
    • disinhibition symptoms due to the autonomous functioning of the thalamus and brainstem
      • flexion movements provoked by sensitive stimuli
      • oral automatisms, tooth grinding, and yawning
      • axial and paraxial syndromes
    • focal signs resulting from localized cortical and subcortical lesions
      • paresis, extrapyramidal disorders
      • oculomotor disorders
Etiology
  • traumatic brain injury (TBI) – cerebral contusions +/- diffuse axonal injury (DAI)
  • repeated ischemic strokes and hypoxia (cardiac and respiratory arrest, strangulation, etc.)
  • less frequently inflammatory, toxic, and metabolic disorders (these etiologies involve internal physiological or biochemical processes that adversely affect brain function)

Minimally conscious state (MCS)

  • MCS, a more recently defined condition, describes patients who recover some signs of awareness in addition to wakefulness
  • these behaviors, although possibly fluctuating and limited in scope due to motor or cognitive constraints, must be unequivocal and reproducible
  • patients in MCS remain unable to communicate functionally by any means, and their interaction with the environment is minimal
  • MCS is categorized into two types based on the observed behaviors:
    • MCS minus (MCS-) – patients show low-level language-independent signs of consciousness (visual fixation, visual pursuit, localization to pain, and oriented movements)
    • MCS plus (MCS+) – patients show higher-level language-related behaviors (command-following, intelligible verbalization, and intentional communication)
  • MCS patients generally have better outcomes than those in UWS, as MCS can be a transient intermediate state leading to functional recovery. However, chronic cases of MCS that persist for extended periods are also common.

Locked-in syndrome

Locked-in syndrome must be excluded in DDx of specific consciousness disorders

Pathophysiology

Synonyms: De-efferentation state, pseudocoma, Sy Monte Cristo, Filimon’s syndrome, ventral pontine syndrome, ventral brainstem syndrome, cerebromedullary disconnection syndrome

  • the only sign of a wakeful state is the preservation of voluntary vertical eye movements
  • syndrome is typically caused by lesions at the base of the brainstem (usually in the pons or midbrain), which damage efferent motor pathways (de-efferentation state).
  • apart from the classic presentation,  incomplete locked-in syndromes with some other residual movements exist
  • the rare total locked-in syndrome is characterized by complete loss of all voluntary motor activity, including eye movements, with unimpaired consciousness and normal or nearly normal EEG
Clinical presentation
  • the patient remains awake, as reticular formation function is preserved
  • quadriplegia results from damage to the corticospinal tract; paresis of distal cranial nerves due to lesions of the corticobulbar and corticopontine tracts, leads to anarthria and aphonia, as well as respiratory and swallowing disorders
  • the patient is unable to voluntarily control breathing and urination and defecation
  • mesencephalic oculomotor function (vertical gaze, eyelid elevation, bulbar convergence, and pupillary responses) and somatosensory and auditory pathways located in the dorsal brainstem remain unaffected
  • disorders of postural reactivity may mimic decerebrate rigidity in response to external stimuli
Etiology
  • most often due to infarcts or hemorrhages occurring in the upper pons or crus cerebri (so-called mesencephalic locked-in syndrome due to occlusion of perforators from the PCA)
  • central pontine myelinolysis
  • brainstem tumor
Differential diagnosis
  • so-called “pseudo-locked-in” syndrome can arise due to:
    • severe polyneuropathy (e.g., Chronic Inflammatory Demyelinating Polyneuropathy – CIDP)
    • neuromuscular transmission disorders (such as myasthenia gravis)
  • locked-in syndrome is characterized by the preservation of vertical eye movements in an individual who is otherwise completely paralyzed
  • communication can be established using a predefined code (e.g., looking down for ‘yes’ and looking up for ‘no’), confirming intact consciousness
  • fluctuations in vigilance, along with additional cognitive or sensory deficits, may contribute to a high rate of misdiagnosis in these cases

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Specific consciousness disorders
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