Comatose patients present to the neurologist in several ways, particularly in the emergency room or intensive care unit. Given the many causes of coma, the central focus is a comprehensive evaluation that starts with a detailed history, although this has to be an account—at least to begin with—from bystanders, paramedics or even the police. This is followed by a neurological and general examination, gathering of key findings, localisation of the involved brain structure, neuroimaging and other laboratory tests. Sorting out the cause of coma is what neurologists do best— compared with other specialists. Of course the relatively recent availability of MRI has helped tremendously in understanding some cases of coma but brain imaging can be normal. Indeed, unravelling the cause of coma remains in many circumstances a clinical judgement.

Once treated, comatose patients can recover suddenly (eg, after quick correction of hypoglycaemia) but many patients have significant structural brain injury and take days to awaken. About 25% of patients stay in a prolonged state of unconsciousness but even then slow awakening is to be expected; only a very small fraction survive but never emerge from coma.