• Clinical science

Persistent vegetative state

Abstract

Persistent vegetative state (PVS) is a clinical condition in which function of the cortex is impaired while function of the brainstem is preserved for a period of more than one month. Traumatic brain injury and diffuse cerebral hypoxia are the most common etiologies. Patients in PVS may appear awake but are not aware or conscious, and they are unable to communicate with others or purposefully interact with their environment. However, they are still able to breathe on their own, sleep-wake cycles are preserved, and autonomic function is at least partially retained. PVS is a clinical diagnosis, and it is important to differentiate it from coma (no sleep-wake cycles) and brain death (no sleep-wake cycles or brainstem function). No definitive treatment exists. Although most patients remain in a vegetative state for years, a few may recover spontaneously. A vegetative state is declared permanent when recovery is very unlikely (i.e., PVS due to trauma lasting more than 1 year or PVS due to a nontraumatic cause lasting more than 3 months).

Etiology

  • Traumatic brain injury
  • Diffuse cerebral hypoxia
  • Other causes of severe damage to the cerebral hemispheres and/or thalamus (e.g., neurodegenerative diseases, CNS infections, metabolic disturbances, toxins, developmental malformations of the CNS)

Pathophysiology

Widespread damage to the white matter of both cerebral hemispheres and/or the thalamus bilaterally, without damage to the brainstem. This results in reduction of cortical function with preserved brainstem control of respiration, cardiac function, sleep-wake cycles, and reflexes.

Clinical features

The condition is typically preceded by traumatic brain injury or diffuse cerebral hypoxia → comatose state requiring intensive care → gradual recovery of autonomic function but lack of recovery of higher mental function after 1 month → PVS with the following features:

  • Intact sleep-wake cycles with periods of wakefulness
  • Loss of perceptual and self-awareness
    • Lack of purposeful response to external stimuli (e.g., tactile, auditory, visual, etc.)
    • Inability to communicate and lack of apparent language comprehension
    • Disconjugate eye movements with loss of fixation
    • Occasional nonpurposeful limb movements and spontaneous smiling, crying, grunting, or screaming
  • Autonomic function and reflexes retained to variable degrees
    • Sufficient cardiovascular, respiratory, and thermoregulatory function
    • Sufficient gastrointestinal and renal function but bowel and bladder incontinence
    • Variable preservation of reflexes (e.g., pupillary, corneal, vestibulo-ocular, gag, cough)

Diagnostics

  • Clinical diagnosis based on ≥ 1 month of intact sleep-wake cycles, loss of perceptual and self-awareness, and autonomic functions retained to variable degrees
  • Neuroimaging
    • CT/MRI: nonspecific diffuse or multifocal abnormalities involving the gray and white matter; decrease in cerebral blood flow
    • PET: diffuse reduction of the glucose metabolic rate of the brain
  • EEG: diffuse generalized polymorphic delta and/or theta activity

Differential diagnoses

Disorders of consciousness
Persistent vegetative state Coma Locked-in syndrome Brain death
Perceptual and self-awareness Absent Absent Present Absent
Sleep-wake cycles Present Absent Present Absent
Motor function No purposeful movement No purposeful movement Quadriplegia and pseudobulbar palsy; eye movement preserved None or only reflex spinal movements
Brainstem reflexes Variable Variable Variable Absent
Respiratory function Normal Depressed, variable Variable Absent

The differential diagnoses listed here are not exhaustive.

Prognosis

  • The vegetative state is defined as permanent if recovery is very unlikely.
  • Likelihood of recovery depends on etiology
    • PVS due to trauma → recovery unlikely after ≥ 12 months
    • PVS due to nontraumatic etiology → recovery unlikely after ≥ 3 months
  • Low life expectancy
  • Withdrawal of life support may be considered if the chances of recovery are very low (e.g., ≥ 12 months in traumatic PVS). However, in patients without advanced directives, it is a complicated legal and ethical question that requires discussion with family members and experts.

Treatment

  • Treatment is supportive; no definitive treatment exists.