Utility of lumbar puncture in the afebrile vs. febrile elderly patient with altered mental status: a pilot study

We conducted a pilot study to compare the diagnostic utility of a lumbar puncture (LP) in febrile vs. afebrile elderly patients with altered mental status (AMS). Our null hypothesis was that there is no utility of performing an LP on the afebrile elderly patient with AMS. A retrospective study was conducted at an urban, university tertiary care referral center. The study population included all elderly patients (age 65 years and older) who had cerebrospinal fluid (CSF) samples sent to the laboratory over 1 year. A structured chart review was performed. Exclusion criteria were normal mental status, recent neurosurgical procedure or presence of a ventricular shunt, and missing medical records. An LP was considered diagnostically useful if it yielded a diagnosis. There were 185 CSF samples from elderly patients recorded over 1 year. Sixty samples were excluded for the following reasons: normal mental status (36), recent neurosurgical procedure (2), presence of ventricular shunt (11), missing medical record (4), repeat LP on same admission (7). Of the 125 patients who met the study criteria, 84 patients were afebrile and 41 patients were febrile. Of the 84 afebrile patients with AMS, 15 patients (18%; 95% confidence interval [CI] 10-26%) had an abnormal LP. Ten (12%) had some form of meningitis and five (6%) had unclear diagnoses. Of the 41 febrile patients with AMS, 10 patients (24%; 95% CI 11-38%) had an abnormal LP. Three (7%) had some form of meningitis or encephalitis. Comparing the elderly patient group without fever with the elderly patient group with fever, there was no statistical difference in the incidence of abnormal LPs or diagnostically useful LPs. Based on the results of this pilot study, we were unable to reject the null hypothesis that there is no utility of performing LP on afebrile elderly patients with altered mental status. We would advocate not relying solely on the presence or absence of fever to determine management in the elderly.