With increasing refinements in the treatment of severe systemic diseases and cerebral injury, larger numbers of patients, who formerly would have died, have survived for indefinite periods without regaining any meaningful mental function. For the first week or two after severe cerebral injury, these patients are in a state of deep coma. Then they begin to open their eyes, at first in response to painful stimuli, and later spontaneously and for increasingly prolonged periods. The patient may blink in response to threat or to light and intermittently the eyes move from side to side, seemingly following objects or fixating momentarily on the physician or a family member and giving the erroneous impression of recognition. Respiration may quicken in response to stimulation, and certain automatisms—such as swallowing, bruxism, grimacing, grunting, and moaning—may be observed (Zeman). However, the patient remains unresponsive and, for the most part, unconscious, does not speak, and shows no signs of awareness of the environment or inner need; motor activity is limited to primitive postural and reflex movements of the limbs. There is loss of sphincter control. There may be arousal or wakefulness in alternating cycles as reflected in partial eye opening, but the patient regains neither awareness nor purposeful behavior.
These features define the vegetative state. One sign of the vegetative state is a lack of consistent visual following of objects, particularly because brief observation of ocular movements is subject to misinterpretation, and repeated examinations are required. These perspectives on the completeness of unresponsivity represent conventional thinking and have been partly altered by the findings of some conscious activity that can be detected by functional imaging with certain commands and verbal cues such as the individual’s name as detailed below.
If the vegetative syndrome of unconscious awakening persists for 3 months after nontraumatic brain injury, and 12 months after traumatic injury, the syndrome has been termed the persistent vegetative state (PVS; Jennett and Plum). These terms have gained acceptance and apply to the clinical appearance whatever the underlying cause. Additional terms that have been used to describe this syndrome of preserved autonomic and respiratory function without cognition include apallic syndrome (also called awake unawareness) and neocortical death. A position paper has codified the features of the PVS and suggests dropping a number of related ambiguous terms, although some, such as akinetic mutism, discussed further on, have a more specific neurologic meaning and are still useful (see Multi-Society Task Force on PVS).
The most common pathologic bases of the vegetative state are diffuse cerebral injury as a result of closed head trauma, widespread necrosis of the cortex after cardiac arrest or other form of anoxia, and thalamic necrosis from a number of causes. The vegetative state or the minimally conscious state described further on, may also be the terminal phase of progressive cortical degenerative processes such as Alzheimer and Creutzfeldt-Jakob disease (where the pathologic changes are mainly cortical but may include the thalamus).
It is worth noting again that the prominent pathologic changes are often in the thalamic and subthalamic nuclei, as in the widely known Quinlan case (Kinney et al) rather than solely in the cortex as often stated; this holds for postanoxic as well as traumatic cases. A review by J.H. Adams and colleagues found these thalamic changes, but attributed them to secondary degeneration from white matter and cortical lesions. However, in several of our cases the thalamic damage stood almost alone as the cause of persistent “awake coma.” In traumatic cases, the pathologic findings are often of diffuse subcortical white matter degeneration (described as diffuse axonal injury), prominent thalamic degeneration, and ischemic damage in the cortex. Further insight is found in a study of brain morphometry by MRI undertaken by Lutkenhoff and colleagues, who determined that in patients with early vegetative or minimally conscious states there was global brain atrophy but the thalamic and basal ganglionic structures were disproportionately affected.