The hinterland of delirium

Abstract

The diagnostic criteria for delirium in the fi fth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) specify a disturbance in attention or change in cognition that is not better accounted for by a pre-existing, established, or evolving dementia; development over a short period; and evidence from the history, physical examination, or laboratory fi ndings that the disturbance is caused by the direct physiological consequences of a general medical condition, is due to an intoxicating substance or medication use, or has more than one cause. Although this defi nition seems unequivocal, delirium is still commonly under-recognised. Descriptions of what we would now know as delirium date back to Classical Greece, with references found in the works of Hippocrates to hyperactive and hypoactive symptoms, which he described with the terms phrenitis (mental abnormalities caused by fever, poisoning, or head trauma) and lethargy (inertia and dulling of the senses). Celus, in the 1st century AD, is generally credited with being the fi rst to use the term delirium to describe mental illness during fever or head trauma, although much debate remains about the etymology of the word. The medical literature throughout the Middle Ages and up to the 19th century is full of descriptions of delirium, although the terminology used varied widely throughout this period, with the designations phrenitis, phrensy, phrenesis, lethargy, paraphrensy, and paraphrenesis falling in and out of favour. During the 20th century, the focus moved away from looking at delirium as only a symptom and more towards understanding of the pathophysiology of the disorder itself. Engel and Romano led the way in this respect in 1959 by showing that delirium was a disturbance in the level of consciousness manifesting as cognitive attentional disturbances and was due to disruption of brain metabolism.