Coma is defined as a sleeplike state in which the patient is unresponsive to self and the environment. Coma should be distinguished from the persistent vegetative state and locked-in syndrome. It is important to obtain a carefully taken history from eyewitnesses and to perform a rapid neurologic examination focusing on pupillary responses, eye movements, and motor responses. Pupils reactive to light usually indicate metabolic or medical coma; cerebellar infarction or hemorrhage is a notable exception. A pupil unreactive to light often points to a structural brain lesion and the need for urgent neurosurgical consultation. The prognosis for coma depends on the cause.
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