A nationwide study on delirium in psychiatric patients from 1995 to 2011.

Objectives: Delirium shares symptoms with some mental illnesses. This may lead to misdiagnosis of delirium in psychiatric patients and a risk of inadequate management. Moreover, literature on delirium in psychiatric patients is sparse. The aim was to analyse possible changes in the diagnostic incidence of delirium in psychiatric patients from 1995 to 2011, and to investigate the patients with regard to sex, age, and type of patient.

Methods: All first time ever diagnoses of delirium among psychiatric patients were identified in the nationwide Danish Psychiatric Central Research Register (DPCRR) from 1995 to 2011. The delirium diagnoses include (1) delirium unspecified, (2) delirium with dementia, and (3) drug-related delirium, all in accordance with International Classification of Diseases-10. The incidence rates were age standardised.

Results: A total of 15 680 persons diagnosed with delirium for the first time were identified in the DPCRR between 1995 and 2011. The total incidence rate of delirium has decreased, reaching 8.4/1000 person-years in 2011. In 2011, 2.6% of the demented patients were diagnosed with delirium with dementia. Diagnosis of delirium is significantly more common in men, and the three groups of delirium showed a characteristic age distribution.

Conclusion: Our incidences were markedly lower when compared with previous studies. This suggests a possible underdiagnosis of delirium in psychiatric hospitals and should be investigated further, as delirium is a serious state and identifying the syndrome is important for sufficient treatment.