Coma can be caused by diffuse injury or dysfunction of the brain’s cerebral cortex or a by a lesion affecting the reticular activating system in the brain stem. A comatose patient is unable to consciously feel, speak, hear, or move.
Brain death is a very severe form of coma with complete loss of brain function. Once this has occurred, the affected patient is legally dead even though the heart, circulation and lungs may still be supported by artificial means. Patients classified as brain-dead can have their organs surgically removed for organ donation.
A patient with locked in syndrome can appear like they are comatose because they can’t move or speak, but they are aware and alert. However, they can usually blink or move their eyes, and may be able to establish communication with others in this way.
There are numerous reported cases of patients with locked in syndrome after strokes or head trauma being misdiagnosed as comatose or even brain dead, some narrowly avoiding having their organs harvested.
If you ever suspect a comatose patient may actually be locked in, you can try to establish communication with eye blinks, or get an EEG which (unlike coma) will be normal and reactive in locked in syndrome.
Patients with locked in syndrome can regain some quality of life:
This plight was made famous in the movie “The Diving Bell And The Butterfly” which was based on a memoir written by journalist Jean-Dominique Bauby.