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Delirium then as now is a nebulous construct in medicine and the sciences that make up its theoretical foundation. Previous attempts at a history of delirium have imposed a coherent whole upon the repository of ideas and statements associated with our modern comprehension. According to Anthony Stevens, there is a developmental history to each medical science. There have been roughly five stages identified that compose this developmental sequence: 1) recognition of features, 2) defining the syndrome, 3) identification of tissue pathology, 4) demonstration of pathogenesis, and 5) discovery and development of cures and treatments (Stevens & Price, 2000: 5). Applying this structure to the conceptual development of delirium may yield a useful perspective when formulating a hypothesis or analysing data pertaining to it. It can be stated confidently that these stages are not clear cut, but rather, are heuristic ideas that organise the history of these developments. When it comes to understanding delirium we can invoke the utility of this paradigmatic motif. However, we must be cognisant of how this conceptual analysis is used as a representation of a continuous historical investigation. Underscoring this position we must also remain aware of the transformation from one paradigm to another in order to question its procedure and theoretical foundation. We must depart from traditional perspectives on delirium that have presented it as an ahistorical entity, and one bordering on a transcendent ideal. Instead, we must focus upon the myriad mutations that have occurred throughout our recorded history of delirium. An interpretation that evokes questions on methods, theories, and limits.

If we accept that the first developmental stage of a medical science is dedicated to the recognition of specific features, then we can discern clearly that the majority of the conceptual history has been concerned with this first stage. Its multiple manifestations across different clinical settings, population, and periods in history support this proposition. The lack of a homogeneous terminology is the result of its peripheral status to medical fields. The lack of standardised terminology also reflects the heterogeneity of its phenotype and its temporal manifestation. There are more terms reflective of delirium than most researchers can imagine or accumulate. The word delirium itself is derived from the Latin deliro/delirare (de-lira, to go out of the furrow), put simply, to be crazy, to rave, to be deranged, to be out of one’s wits (Lewis et al., 1879). It has a metaphorical dimension that links it to agriculture. It was first used by Celsus in the first century AD in his medical writing to describe mental disorders, both as a symptom and syndrome following head trauma or fever (Celsus 2.7). Celsus, who was not a physician, but an encyclopaedist, compiled the Hippocratic Corpus, translated it into Latin, and integrated it with his work De Medicina. He also identified it as a sign of approaching death (Celsus, 1935).

There is of course a plethora of other terms coined to try to capture this phenomena. The father of western medicine, Hippocrates of Cos believed in a materialistic account of mental disorders. Hippocrates established a rational system for medicine and organised disease in terms of categories, acute and chronic, endemic and epidemic. Other medical terms are attributed to him such as relapse, crisis, paroxysm, convalescence, and resolution (West, 2006; Fox, 2008). In keeping with his materialistic perspective, he believed that delirium was a disorder of the brain (Liposki, 1990: 5). Hippocrates never used the term delirium because it was a Latin word and he spoke/wrote in Greek. Instead, Hippocrates described delirium in terms of lethargus and phrenitis, the former referring to dulling of the senses and motor retardation, the latter referring to sleep disturbances, and the acute onset of cognitive and behavioural disturbances generally found in the context of fever. The fluctuation of lethargus and phrenitis was believed by Hippocrates to be a potential part of its clinical course (Lipourlis, 1983). Translations of Galen’s works by Hynayn ibn Ishaq from Greek to Arabic enabled Islamic medicine to utilise his systematic and rational approach to medicine as a template for their future endeavours (French, 2003). The Arab Physician Najab ub din Unhammad in the 8th century, refers to a state of souda (mild delirium) as becoming jannon (severe delirium) associated with insomnia, restlessness, and agitation (Graham, 1967).

At the beginning of the 18th century, phrensy/phrenesis was separated from delirium, whereby, delirium was reserved for a state of brief madness, while phrensy and phrenesis, was associated with febrile conditions and related medical problems. To be more precise, phrensy/phrenesis and paraphrenesis were subdivided to refer to inflammation of the brain versus inflammation of the other organ systems respectively. Inconsistently, paraphenesis was also used to describe the prodromal or beginning stage of delirium (Adamis et al., 2007). The rise of epidemiology to tackle disease on a public scale, the role of micro-organisms to account for infection, and the continued enhancement of medical equipment all saw a sharp distinction in the quality of medicine in the 19th century (Porter, 1997). However, the 19th century developments in delirium research continued to employ terms with accumulating ambiguity. Linguistic dimensions of the words to describe delirium complicated the matter further, for instance, in French the word delire was employed to denote phrenesis and delusions (Berrios, 1981; Berrios & Porter, 1995). The term confusion mentale (Chaslin, 1895) was introduced to account for delirium as a result of organic causes, while other French authors employed terms such as idiotisme asquis (Pinel, 1809), demence aigui (Esquriols, 1814) and stupidite (Georgets, 1820). In German, the term verwirrtheit was used to describe features associated with delirium (Wille, 1888). In 1817, the main feature of delirium was proposed to be the clouding of consciousness. It was proposed that the state of fever induced disturbances in the organ of consciousness, the brain. The course and severity of delirium depended on this dynamic interplay between the fever and the brain. In clear terms, fever and consciousness fluctuated congruently whilst occasionally this was interrupted by lucid periods. It was also maintained that delirium was a state of dreaming whilst awake (Greiner, 1817). During the 1860s, John Hughlings Jackson continued research into the relationship between the clouding of consciousness and the psychopathology of delirium (Lipowski, 1990; 1991; Hogan & Kaiboriboon, 2003).

It was not until the end of the 19th century that many of the classical terms such as lethargus, phrenitis, phrensy, and paraphrenesis began to disappear from the medical discourse. The taxonomic preoccupation of this discourse was replaced with a focus on the disturbances of consciousness and its relationship to sleep and dreaming (Greiner, 1817). In the late 19th century, Emil Kraepelin described in the early edition textbooks on psychiatry, acute onset psychotic states with delusions, significant mood alterations, and vivid hallucinations that vanished abruptly. The term period delirium was introduced in the 4th edition of his textbook (Kraepelin, 1893). The 5th edition saw period delirium turned into a subtype of delirious mania (Kraepelin, 1896). In the 6th edition manic depressive illness was integrated with delirious mania (Kraepelin, 1899). However, Kraepelin was aware that such conditions were not synonymous and explicitly stated that delirious mania ‘must be classed with manic-depressive illness only with a certain reservation’ (Kraepelin, 1904). However, in the 8th edition, Kraepelin removed the note and categorised both conditions together (Kraepelin 1913). In 1924, Carl Kleist, following on from the work of Carl Wernicke, coined the term cycloid psychosis to describe the phenomena that ‘manifest themselves in multiple phases during life, come and go in an autochthonous way, often show antagonistic syndromes - confusion and stupor, hyperkinesis and akinesis - and do not lead to mental defects’. In addition, he described cycloid psychosis in terms of confusional psychosis and motility psychosis; such descriptions are arguably the same as the modern conception of delirium (Kleist, 1924; 1928). In 1962, Maurice Victor and Raymond Adams proposed the classification of confusional states, including delirium, primary mental confusion, and beclouded dementia (Victor & Adams, 1962). In the modern era, ICU syndrome or ICU psychosis became prevalent and was associated with both the ICU environment as well as underlying critical illness (McGuire et al., 2000). The term oneirism was used in the modern context to describe the alterations in behaviour and perception that resemble dreams during delirious states (Sellal & Collard, 2001). Delirium was until recently defined in the revised 4th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) as a ‘disturbance of consciousness with cognitive changes or perceptual disturbance, which has developed over a short period of time, and is caused by a general medical condition' (APA, 2000). With the publication of the new edition DSM-5, delirium is now redefined in terms of reduced awareness and inattention, while removing the term consciousness altogether. Such an alteration has been suggested to substantially impact both clinical care and research in the context of its interpretation (Meagher et al., 2014).

The terms used to denote delirium, including the word delirium itself, attempt to encapsulate at once the idea that it is a singular entity distinct from other phenomena. But such a word also tries to capture the notion that it is embedded within a register of abnormal relations, without subscribing it to the status of an epiphenomenal entity.


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