[Approach to the patient in vegetative state. Part I: diagnosis]

Coma is the condition in which both components of consciousness, wakefulness and awareness, are lost. Therefore, the comatose patient neither opens the eyes, nor utters comprehensible words or follows commands. In the vegetative state (VS), awareness (including all cognitive function and emotion) is lost, while the vegetative functions, including breathing and sleep-wake cycles (the wakefulness), persist. Usually VS follows a state of coma caused by traumatic or anoxic brain damage. Pathologic brain examination demonstrates extensive subcortical, white matter, bilateral thalamic, and brainstem lesions in various combinations. Bilateral cerebral cortical lesions are rare, and therefore cortex can be "out of action" despite unaltered structure. More rarely, VS is caused by brain developmental malformations in children, or metabolic or degenerative diseases in children and adults. These are the only cases in which patients are not comatose before VS becomes apparent. After 6-8 weeks of coma, patients regain the eye opening. In such a condition, the term coma is no longer appropriate. If awareness is absent, the patient can be defined as in VS. Finally, the VS is defined as persistent (PVS) when it has continued for at least 1 month. The diagnosis of VS and PVS are clinical and require assessment over an adequate period of time and the skills of a multidisciplinary experienced team. Diagnosis is very complex in infants younger than 3 months, and is not applicable to preterm neonates, with the unique exception of infants with anencephaly. Among ancillary diagnostic tools, dynamic PET studies show promise.