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In hospital and emergency neurology, the clinical analysis of unresponsive and comatose patients becomes a practical necessity. There is always an urgent need to determine the underlying disease and the direction in which it is evolving in order to protect the brain against more serious or irreversible damage. When called upon, the physician must therefore be prepared to implement a rapid, systematic investigation of the comatose patient and prompt therapeutic and diagnostic action that allows little time for deliberate, leisurely investigation.

Some idea of the dimensions of the problem of coma can be obtained from published statistics. Eighty years ago, in two large municipal hospitals, it was estimated that 3 percent of all admissions to the emergency wards were for diseases that had caused coma. Alcoholism, cerebral trauma, and cerebrovascular diseases were the most common, accounting for 82 percent of the comatose patients admitted to the Boston City Hospital (Solomon and Aring). Epilepsy, drug intoxication, diabetes, and severe infections were the other major causes for admission. It is perhaps surprising to learn that more contemporary figures from large city hospitals are much the same; they emphasize that the common conditions underlying coma are relatively invariant in general medical practice. For example, in the series collected by Plum and Posner (Table 17-1), only 25 percent proved to have cerebrovascular disease, and in only 6 percent was coma the consequence of trauma. Indeed, all intracranial masses and their secondary effects—such as tumors, abscesses, hemorrhages, and infarcts—made up less than one-third of the coma-producing diseases. A majority was the result of exogenous (drug overdose) and endogenous (metabolic) intoxications and hypoxia. Subarachnoid hemorrhage, meningitis, and encephalitis accounted for another 5 percent of the total. Thus, intoxication, stroke, and cranial trauma stand as the "big three" of coma-producing conditions. Equally common in some series, although obvious and usually transient, is the coma that follows seizures or resuscitation from cardiac arrest.

Table 17-1 Final Diagnosis in 500 Patients Admitted to Hospital with "Coma of Unknown Etiology"

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