Depressed mental status represents an alteration in arousal and is
a common presenting complaint in the emergency department
(ED). This presentation can be the manifestation of a wide spectrum
of diseases, with the degree of impairment ranging along a
continuum from sleepiness to decreased alertness to frank coma.
The differential diagnosis of stupor and coma is broad and diverse
(Table 16-1) but can usually be categorized into metabolic and
systemic, structural, or psychogenic causes. The majority of cases
are caused by metabolic or systemic derangements, whereas the
remainder are usually caused by structural lesions. Psychogenic
presentations are much less common. The differential diagnosis
for depressed level of consciousness often overlaps with that for
confusion (see Chapter 17). Frequently, diagnosis and management
occur simultaneously, and a structured systematic approach
is used. A thorough grasp of the underlying pathophysiology
leading to the acute depressed mental state will lead to timely
diagnosis and treatment.