There are a large number of causes of coma, and it is convenient to classify them as those producing diffuse bihemispheric dysfunction and those with structural lesions producing mass effect (Brock..aDd Bleck.!995)■ Some of the major causes are listed in Table 1. Non-convulsive status epilepticus may present as unresponsiveness. Subtle signs, such as eyelid fluttering, mild facial twitching, or nystagmus, may be the only evidence that the patient is having a seizure. Similarly, a postictal state may show prolonged unresponsiveness and include focal signs of hemiparesis (Todd's paralysis) or posturing.
Psychiatric conditions mimicking coma include catatonia, conversion reactions, and feigned coma. In these conditions, pupillary responses and ocular movements will be normal. The motor examination may demonstrate normal tone in supposedly paretic limbs, and the patient will have normal movements when asleep.
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