Subsyndromal delirium and its determinants in elderly patients hospitalized for acute medical illness

BACKGROUND: In older individuals, acute medical illnesses and admission to hospital are often associated with a deterioration of cognitive status, also in the absence of dementia and full-blown delirium. We evaluated the prevalence of subsyndromal delirium (SSD) and its correlates in a sample of elderly medical inpatients. METHODS: From 763 consecutive inpatients, 325 participants with known dementia or delirium were excluded, whereas 438 (mean age: 80.6 years; female participants: 60.1%) were enrolled. SSD was diagnosed within 48 hour from admission, when at least two DSM-IV delirium criteria including disorientation, attention or memory deficit, altered level of consciousness, or perceptual disturbances were present. Cognitive performance was evaluated by Mini Mental Status Examination (MMSE). General, clinical, and laboratory parameters were also registered. RESULTS: One hundred and sixty-six patients (37%) had SSD. Compared with controls, SSD patients were older individuals, had less formal education, higher comorbidity, lower hemoglobin/lymphocytes counts, and higher creatinine levels. A trend toward higher prevalence of previous stroke and widowhood was observed. A MMSE score of less than 24/30 identified SSD with 88% sensitivity and 78% specificity. In SSD patients, MMSE independently correlated with years of education, high-sensitivity C reactive protein levels, and O2 arterial saturation (model adjusted r (2) = 0.30, p = .001); conversely, only years of education were associated with MMSE in controls (adjusted r (2) = 0.06, p = .01). CONCLUSIONS: Our data suggest that SSD is common in hospitalized older medical inpatients, and low MMSE score might be useful for identification of participants at risk of SSD. Current inflammatory response and reduced O2 arterial saturation were the only independent determinants of cognitive performance in SSD patients.