Features of subsyndromal and persistent delirium

Declaration of interest

P.T. is a full-time salaried employee and shareholder at Eli Lilly and Company.

David Meagher, University of Limerick Medical School, Limerick, Ireland. Email: [email protected]

Delirium is a complex neuropsychiatric syndrome occurring in 11-42% of general medical in-patients, ¹ with even higher rates in older patients, those with pre-existing cognitive impairment, terminal illness or receiving care in intensive care units. ² Although delirium is classically described as a syndrome with high inherent reversibility, studies have increasingly highlighted that persistence is a common occurrence in older people. ³ Despite its relatively high incidence and potential for a range of negative outcomes including higher mortality and reduced independent functioning in elderly people, delirium remains seriously understudied. ⁴ Recent cross-sectional studies that utilise more detailed measurement methods provide a valuable insight into the symptoms that occur most frequently and at greater severity in patient groups with delirium. ^5-8 However, longitudinal studies that focus on describing severity, temporal course or symptom pattern of delirium episodes are relatively lacking; Fann et al ⁹ used the Delirium Rating Scale (DRS) and Memorial Delirium Assessment Scale (MDAS) items together for daily ratings, Sylvestre et al ¹⁰ used the Delirium Index to describe overall patterns of severity and Rudberg et al ¹¹ reported daily scores on the DRS in surgical patients. However, only Fann et al reported individual symptoms over time. Therefore, the pattern, inter-relationships and temporal course of symptoms during episodes are still not well understood.

Elucidating subsyndromal delirium symptoms could serve to enhance early recognition of individuals at risk for delirium or poorer outcomes. Identification of delirium symptoms that occur in individuals who do not meet full diagnostic criteria either as a prodrome, milder state or transient recovery phase has not yet revealed specific symptoms that could consistently define a state of subsyndromal delirium. ⁷ Subsyndromal delirium, as variously defined, appears to carry prognostic significance for adverse outcomes that are intermediate between full syndromal delirium and controls (for example, decreased post-discharge level of functional independence, elevated mortality, increased length of stay). ^12-16 However, DSM-IV ¹⁷ criteria are known to be the least restrictive to diagnose delirium ¹⁸ as compared with ICD-10 ¹⁹ and DSM-III-R ²⁰ and therefore likely to incorporate individuals with milder and subsyndromal delirium under its umbrella.