DO SURGICAL BRAIN-LESIONS PRESENT AS ISOLATED DEMENTIA - A POPULATION-BASED STUDY

OBJECTIVE: To determine the incidence of clinically important subdural hematoma (SDH), hydrocephalus not associ ated with a recent intracran ial bleed, and intracranial tumor that is not obviously metastatic, an d to test the sensitivity of a promising decision rule for computerize d tomography (CT) in dementia. DESIGN: Population-based, retrospective , sequential case series. SETTING: Staff model health maintenance orga nization (HMO). PATIENTS: Patients aged 65 years and older with one of the three lesions, diagnosed over a 4.5-year period, identified mainl y through computerized databases of hospital discharge diagnoses and a registry of malignant tumors. MEASUREMENTS: Clinical data were based on chart review. The decision rule, based on one that had been previou sly proposed and tested, stated that CT would be required if any one o f 11 clinical criteria were met by a patient with cognitive impairment . Rule sensitivity was evaluated using clinical information recorded b efore CT. MAIN RESULTS: One hundred forty-five clinically important le sions were identified among 137,100 person-years at risk. Average annu al incidence per 100,000 was 46.7 (95% CI 36.0, 59.6) for SDH, 5.8 (95 % CI 2.5, 11.5) for hydrocephalus not associated with a recent intracr anial bleed, and 53.2 (95% CI 41.7, 66.9) for intracranial tumors that were not obviously metastatic. Using the 65 to 74- year age strata as a reference, the relative risk for SDH was 4.8 (95% CI 2.7, 8.5) in 7 5 to 84-year-olds and 13.1 (95% CI 7.7, 22.5) in the 85 and older stra ta. Among 59 patients who presented with cognitive impairment, without altered sensorium or physical evidence of trauma, decision rule sensi tivity was 93.2% (95% CI 83.5%, 98.1%). Sensitivity was 90.7% (95% CI 77.9%, 97.4%) in the subgroup that presented to an ambulatory care cli nic rather than to an emergency department. CONCLUSIONS: These three l esions, which are the most common surgical lesions that may present as dementia, are rare. Most cases have presentations that easily disting uish them from typical Alzheimer's disease. This case series indicates that it may be feasible to develop a decision rule for the selective use of CT in dementia. Disease spectrum will influence measures of dec ision rule performance such as sensitivity and specificity.