Undiagnosed long-term cognitive impairment in acutely hospitalised older medical patients with delirium: a prospective cohort study

Background: delirium and dementia are common in the general hospital, being present in nearly 50% of older unselected admissions to hospital. Cognitive impairment is a risk factor for delirium, but the prevalence of previously undiagnosed cognitive impairment (dementia or mild cognitive impairment) in patients with delirium is unknown. Methods: we performed a prospective cohort study of people over 70 years admitted to hospital with delirium to establish the prevalence of previously unrecognised prior cognitive impairment. Delirium was diagnosed at baseline using the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR). Mild cognitive impairment and dementia were diagnosed 3 months following recruitment in survivors using the International Working Group on Mild Cognitive Impairment criteria and DSM-IV criteria, respectively. Results: delirium was identified in 17.9% of older patients, and 82 participants with delirium were assessed at 3 months: 5 (6%) had persistent delirium, 14 (17%) had mild cognitive impairment and 47 (57%) had dementia. In 17 participants with prior dementia and 14 with prior mild cognitive impairment, the diagnosis had been unrecognised, amounting to 31/82 (38%) of all patients with delirium having some form of previously undiagnosed cognitive impairment. Conclusion: given that over 1/3 of older patients with delirium were found to have a previously undiagnosed cognitive impairment, the development and evaluation of services to follow-up and manage patients with delirium are warranted.