The many mental and behavioral aberrations that are seen in confused patients, and their occurrence in various combinations and clinical contexts, make it unlikely that all forms of confusion derive from a single elementary mental or neurobiological abnormality. While attention is certainly near the core of confusion, and is considered the germinal feature by some investigators, phenomena as diverse as drowsiness and stupor, hallucinations and delusions, disorders of perception and registration, impersistence and perseveration, and so forth are not easily reduced to one mechanism. It seems more likely that a number of separable or overlapping disorders of function are involved. Indeed, one view of the confusional state that we find attractive conceptualizes confusion as a loss of the integrative functions among all the elementary and localizable cerebral functions such as symbolic language, memory retrieval, and apperception (the interpretation of primary perceptions). All of these are included under the rubric of the confusional state, for want of a better term.
As commented, we prefer to use the term delirium to denote a highly recognizable agitated and hypersympathetic form of confusion. In addition to many of the negative elements of incoherent thinking mentioned above, delirium defined this way is characterized by a prominent disorder of perception; hallucinations and vivid dreams; a kaleidoscopic array of strange and absurd fantasies and delusions; inability to sleep; a tendency to twitch, tremble, and convulse; and intense fear or other emotional reactions. Delirium is distinguished not only by extreme inattentiveness but also by a state of heightened alertness—an increased readiness to respond to stimuli—and by overactivity of psychomotor and autonomic nervous system functions, sometimes striking in degree. Implicit in the term delirium are its nonmedical connotations as well—namely, intense agitation, or frenzied excitement, and trembling. This distinction between delirium and other acute confusional states is not universally accepted. Many authors attach no particular significance to the autonomic and psychomotor overactivity and the hallucinatory and dream-like features of delirium, or to the underactivity and somnolence that characterize most other confusional states. We continue to find it useful to set delirium apart from other nondescript confusional states, if only for instructional purposes, because the two are manifestly different and occur in different clinical contexts. Engel and Romano called delirium “a state of cerebral insufficiency” and provided one of the fullest clinical descriptions of the syndrome and the monograph by Lipowski may be consulted. Implicit in both designations is the idea of an acute, transient, and usually relatively reversible disorder.
Impairment of memory is often included among the symptoms of delirium and other confusional states. Registration and recall are indeed greatly reduced in the states under discussion, but they are affected in proportion to the degree of inattention and the inability to register new material. The term amnesia, refers more precisely to an isolated loss of past memories as well as to an inability to form new ones, despite an alert state of mind and normal attentiveness. Amnesia further presupposes an ability of the patient to grasp the meaning of what is going on around him. The failure in the amnesic state is one of retention, recall, and reproduction and must be distinguished from states of drowsiness, acute confusion, and delirium, in which information and events seem never to have been adequately perceived and registered in the first place. In both a confusional state and in amnesia, the patient is left with a permanent gap in memory for his acute illness.
In a similar way, the term dementia (literally, an undoing of the mind) denotes a deterioration of all intellectual or cognitive functions with little or no disturbance of consciousness or perception. Implied in dementia is the idea of a gradual degradation of mental powers in a person who formerly possessed a normal mind. Amentia, by contrast, indicates a congenital feeblemindedness more commonly referred to as mental retardation, or more properly, developmental cognitive delay. Dementia and amnesia are discussed more explicitly in Chap. 20.