Delirium is a serious neuropsychiatric syndrome affecting mainly elderly participants with acute medical diseases. The pathophysiology of delirium remains poorly understood as it involves complex dynamic interactions between a diversity of risk factors. Exploring how etiological factors interact with each other can clarify the pathophysiological mechanisms and facilitate the early identification of this syndrome. The aim of this study was to explore how different risk factors co-occur in medically ill elderly patients with delirium with cluster analysis and identify clinically meaningful sub-groups in this population.

A cross-sectional study was developed. Ninety-nine elderly inpatients admitted to acute medical wards diagnosed with delirium during hospitalization were selected. For each patient sociodemographic characteristics, acute and chronic medical conditions, laboratory parameters, and current medication were collected.

The cluster analysis extracted three distinct subgroups of participants with delirium. Patients in cluster 1 (n = 28) had higher rates of medication with anticholinergic proprieties. Cluster 2 (n = 29) included participants with cardiac and pulmonary comorbidities associated with both chronic and acute reduction of blood flow and/or oxygenation to the brain. Cluster 3 (n = 42 patients) comprised patients with simultaneous deregulation of different organs/systems, such as electrolytic disturbances, metabolic disturbances, and acute renal failure. Known predisposing factors of delirium, such as age and pre-existing dementia, were similar between groups.

The results reveal different patterns of clinical characteristics in elderly patients with delirium. This is relevant to clinical care of acute medically ill patients and suggests that different pathways are implicated in delirium pathophysiology.