Current controversies in states of chronic unconsciousness

Abstract

Coma resulting from brain injury or illness usually is a transient state. Within a few weeks, patients in coma either recover awareness, die, or evolve to an eyes-open state of impaired responsiveness such as the vegetative or minimally conscious state. These disorders of consciousness can be transient stages during spontaneous recovery from coma or can become chronic, static conditions. Recent fMRI studies raise questions about the accuracy of accepted clinical diagnostic criteria and prognostic models of these disorders that have far-reaching medical practice and ethical implications. A 21-year-old woman lost control of her car and struck a bridge abutment. She sustained a severe traumatic brain injury (TBI) with subdural, subarachnoid, and intracerebral hemorrhages that was complicated by intracranial hypertension and generalized seizures. When examined in the neurorehabilitation center 6 months later, she was in a vegetative state with eyes-open wakefulness but without awareness of herself or her environment, no psychological responsiveness, and marked spasticity with little movement of her limbs. Her eyes were open and moving when she was awake and were closed when she was asleep. Brain CT scan showed bilateral thalamic and multifocal cortical areas of encephalomalacia with ex vacuo hydrocephalus. Her EEG had an irregular 4-Hz background with intermittent sharp waves over the right hemisphere. Six months later, her parents reported that she had become responsive. The examiner could, at times, get her to follow a $20 bill with her eyes and to reach toward it but she followed no commands. Her pupillary light reflexes were normal and she had roving, full eye movements. Most of the time, examiners and staff members could elicit no responsiveness. She breathed spontaneously through a tracheostomy tube and was fed and hydrated by a gastrostomy tube. She required daily physical therapy to prevent contractures that had developed in all her limbs. Repeat brain imaging and EEG were unchanged. Her parents asked if she could undergo fMRI assessment which they discovered on an Internet search might prove that she was aware and could improve. DIAGNOSTIC ISSUES The vegetative state (VS) and minimally conscious state (MCS) are the principal clinical syndromes of patients with chronically disordered consciousness. As syndromes, they encompass a spectrum of severity and can be the consequence of a variety of brain injuries and illnesses. 1 Categorizing patients with disorders of consciousness into the correct diagnostic syndrome is essential, but the prognosis of each patient depends mostly on the cause and extent of the brain damage producing the syndrome. The VS has been epitomized as “wakefulness without awareness” because the brainstem reticular system responsible for alertness and wakefulness remains intact but the thalamocortical systems responsible for awareness have been damaged. The VS is best conceptualized as a disconnection syndrome between the thalami and the cortex resulting from 1) bilateral thalamic damage; 2) diffuse cortical damage, especially involving the precuneus; or 3) damage to the white matter tracts connecting the thalami and cortex. The principal causes of VS are 1) TBI, which can cause damage by all 3 mechanisms, but especially by white matter tract damage from severe diffuse axonal injury because of rotational brain trauma; 2) hypoxic-ischemic neuronal damage to the