The prognostic significance of subsyndromal delirium in elderly medical inpatients.

OBJECTIVES: To determine the prognostic significance of subsyndromal delirium (SSD) presentations.
DESIGN: Cohort study.
SETTING: University-affiliated primary acute care hospital. PARTICIPANTS: One hundred sixty-four elderly medical inpatients who did not meet Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R) criteria for delirium during the first week after admission were classified into three mutually exclusive groups. The first group, prevalent SSD, included those who had two or more of four core symptoms of delirium (clouding of consciousness, inattention, disorientation, perceptual disturbances) at admission. The second group, incident SSD, included those who did not meet criteria for prevalent SSD but displayed one or more new core symptoms during the week after admission. The third group had no prevalent or incident SSD. The three groups were followed up at 2, 6, and 12 months. MEASUREMENTS: Outcomes (length of stay, symptoms of delirium (Delirium index), cognitive (Mini-Mental State Examination) and functional status (instrumental activities of daily living), and mortality) were compared using univariate techniques and multivariate regression models that adjusted for age, sex, marital status, living arrangements before admission, comorbidity, clinical and physiological severity of illness, and dementia status and severity.
RESULTS: Patients with prevalent SSD had longer acute care hospital stay, increased postdischarge mortality, more symptoms of delirium, and a lower cognitive and functional level at follow-up than patients with no SSD. Most of the findings for incident SSD were similar but not statistically significant. Patients with prevalent or incident SSD had risk factors for DSM-defined delirium.
CONCLUSION: SSD in elderly medical inpatients appears to be a clinically important syndrome that falls on a continuum between no symptoms and DSM-defined delirium.