Differences Between Persistent Vegetative State (PVS) and Coma
The key difference between persistent vegetative state (PVS) and coma is that PVS patients show wakefulness without awareness (sleep-wake cycles with open eyes but no cognitive function), while coma patients show neither wakefulness nor awareness (eyes remain closed with no sleep-wake cycles).
Diagnostic Criteria
Coma
- Characterized by complete absence of both wakefulness and awareness 1
- Eyes remain closed with no sleep-wake cycles 2
- Caused by damage to bilateral cerebral hemispheres or reticular activating system 1
- May result from neurogenic (brain injury), metabolic (endogenic), or toxic (exogenic) factors 1
- Typically assessed using Glasgow Coma Scale or Full Outline of Unresponsiveness Scale 1
Persistent Vegetative State (PVS)
- Characterized by wakefulness without awareness or cognitive function 2, 3
- Eyes open with preserved sleep-wake cycles 2, 3
- Patients appear awake but show no evidence of awareness of self or environment 4
- Defined as vegetative state that has continued for at least one month 2
- Primarily involves damage to cerebral cortex with relatively preserved brainstem function 3
Clinical Features
Coma
- No eye opening, even to painful stimuli 1
- Absence of sleep-wake cycles 1
- No purposeful motor responses 1
- Impaired brainstem reflexes may be present depending on the cause 1
- Usually a temporary state that evolves to death, recovery, or other conditions like PVS 5
Persistent Vegetative State (PVS)
- Spontaneous eye opening and sleep-wake cycles 2, 3
- Preserved brainstem reflexes (pupillary light, corneal, oculocephalic) 3
- Non-purposeful movements of extremities 3
- No evidence of language comprehension or expression 4
- No purposeful behavioral responses to environmental stimuli 4
Electrophysiologic Differences
Coma
- EEG typically shows generalized slowing or suppression 1
- Somatosensory evoked potentials (SSEPs) may be absent or severely abnormal 1
- Brain stem auditory evoked potentials (BAEPs) may be abnormal depending on the cause 1
Persistent Vegetative State (PVS)
- EEG shows ample low amplitude and nonspecific slow waves, not isoelectric 3, 6
- Median nerve somatosensory evoked potentials (SSEPs) show absence of cortical response 3, 6
- Brain stem auditory evoked potentials (BAEPs) are normal or only slightly abnormal 3, 6
- These findings suggest damage primarily to cerebral cortex rather than brainstem 3
Prognosis
Coma
- Generally a temporary condition lasting days to weeks 5
- Outcomes depend on etiology, patient age, comorbidities, and timeliness of treatment 1
- May progress to death, recovery, or transition to other states like PVS 5
Persistent Vegetative State (PVS)
- Recovery is extremely unlikely after one year of post-traumatic PVS or after three months of non-traumatic PVS 4
- Prognosis can be predicted based on etiology and age 2
- Patients can be subdivided into groups based on outcome probabilities and etiology 2
Management Approaches
Coma
- Focus on identifying and treating the underlying cause 5
- Ensuring adequate oxygenation and correcting blood circulation disorders 1
- Treatment varies based on etiology: specific schemes for metabolic coma, antidotes for toxic coma, and surgery for traumatic brain injury 1
Persistent Vegetative State (PVS)
- Three levels of care can be provided: high technology, supportive, and compassionate care 2
- Management decisions should involve shared decision-making between physicians and family 2
- For nutrition, the Clinical Nutrition society recommends artificial nutrition and hydration in cases of uncertain prognosis, while considering advance directives or the presumed will of the patient 4
- Instrumental tools such as fMRI, EEG, and PET can improve diagnostic accuracy 4
Assessment Tools
Coma
- Glasgow Coma Scale or Full Outline of Unresponsiveness Scale for level of consciousness 1
- Evaluation of pupillary reactions, oculomotor responses, motor responses, and cardiopulmonary function 1
Persistent Vegetative State (PVS)
- Coma Recovery Scale-Revised for accurate diagnosis of consciousness level 4
- Advanced neuroimaging techniques like fMRI, EEG, and PET can detect covert awareness not apparent on clinical examination 4
- Regular reassessment is essential as some patients may show signs of minimal consciousness over time 4