Diagnostic Yield of Combined Lumbar Puncture and Brain MRI in Critically Ill Patients With Unexplained Acute Encephalopathy: A Retrospective Cohort Study.

Critically ill patients frequently experience acute encephalopathy, often colloquially termed "altered mental status" (AMS); however, there are no consensus guidelines or criteria about performing lumbar puncture (LP) and advanced neuroimaging in medical ICU patients with unexplained encephalopathy.

Objectives: We sought to characterize the yield of combined LP and brain MRI (bMRI) in such patients as determined by both the frequency of abnormal results and the therapeutic efficacy of these investigations, that is, how often results changed management.

Design setting and participants: Retrospective cohort study of medical ICU patients admitted to a tertiary academic center between 2012 and 2018 who had documented diagnoses of "AMS" and/or synonymous terms, no clear etiology of encephalopathy, and had undergone both LP and bMRI.

Main outcomes and measures: The primary outcome was the frequency of abnormal diagnostic testing results determined objectively for LP using cerebrospinal fluid (CSF) findings and subjectively for bMRI through team agreement on imaging findings deemed significant through retrospective chart review. We subjectively determined the frequency of therapeutic efficacy. Finally, we analyzed the effect of other clinical variables on the likelihood of discovering abnormal CSF and bMRI findings through chi-square tests and multivariate logistic regression.

Results: One hundred four patients met inclusion criteria. Fifty patients (48.1%) had an abnormal CSF profile or definitive microbiological or cytological data by LP, 44 patients (42.3%) had bMRI with significant abnormal findings, and 74 patients (71.2%) had abnormal results on at least one of these investigations. Few clinical variables were associated with the abnormal findings in either investigation. We judged 24.0% (25/104) of bMRI and 26.0% (27/104) of LPs to have therapeutic efficacy with moderate interobserver reliability.

Conclusions: Determining when to perform combined LP and bMRI in ICU patients with unexplained acute encephalopathy must rely on clinical judgment. These investigations have a reasonable yield in this selected population.