[Delirium: etiology and pathophysiology]

The physiopathology of delirium has still not been characterized in depth, although this entity can be defined as a functional brain disorder provoked by one or multiple organic causes that display a common clinical syndrome. Certain specific brain regions that are involved in delirium have been identified, such as the prefrontal cortex, the thalamus and the basal ganglia, especially in the nondominant hemisphere. Functional changes occur in a large number of neurotransmitters: the most frequent and best characterized are a reduction of cholinergic function and an increase in dopaminergic and gabaergic function, although alterations in almost all neurotransmitter systems (serotoninergic, noradrenergic, glutaminergic, histaminergic) have been found. Inflammation also seems to play an important role, at least in some types of delirium. Delirium in the elderly typically has a multifactorial etiology, with several simultaneous or sequential causes. Numerous risk factors have been described, both predisposing individuals to delirium and triggering this syndrome. Knowledge of these factors and their interactions is of great clinical importance and consequently etiologic diagnosis should be based on a multifactorial model.