102. Accuracy of physical examination on ruling out cauda equina syndrome (CES): is MRI necessary?

BACKGROUND CONTEXT Cauda equina syndrome (CES) is defined as the severe compression of the cauda equina resulting in loss of lower sacral nerve root function. There are no studies to date that demonstrate whether physical examination can accurately diagnose CES, therefore providers feel obligated to order magnetic resonance imaging (MRI) studies on patients reporting bowel or bladder dysfunction with associated low back pain to rule out a diagnosis of CES. PURPOSE The purpose of this study is to evaluate the utility of a series of physical examinations in diagnosing or ruling out CES. STUDY DESIGN/SETTING A retrospective cohort study of adult patients at a single academic medical center from January 1, 2008 to December 31, 2017. PATIENT SAMPLE Adult back pain patients presenting with bowel or bladder dysfunction who received a lumbar MRI in the emergency department. Patients were excluded if their lesions were due to trauma or tumor. OUTCOME MEASURES Sensitivity, specificity, negative, and positive predictive values for each component of the physical examination (rectal tone, perianal sensation, bulbocavernosus reflex [BCR]) and post-void residual bladder (PVR) compared to CES diagnosis (defined as complete or near complete occlusion of the spinal canal on MRI). METHODS Chart and imaging review was performed to collect data regarding physical examinations, PVR measurements, and treatment (surgery or no surgery). Physical examinations studied include perianal sensation, rectal tone, and BCR. PVR was defined as positive if measured at ≥300 mL. CES was defined as complete or near complete occlusion of the spinal canal on MRI requiring immediate surgical intervention. Analyses, including sensitivity, specificity, negative, and positive predictive values for each physical examination and PVR were performed using SAS. Fast-and-Frugal decision tree (FFT) analysis was done in R to determine the predictive value of physical examination combinations. RESULTS Of the 2,751 lumbar MRIs obtained, 142 patients met the inclusion criteria of bowel or bladder dysfunction associated with lower back complaints. Ten patients were confirmed to have CES by MRI. The sensitivity and specificity of the exam findings were as follows: rectal tone 80% and 86%, perianal sensation 60% and 68%, PVR 80% and 59%, and BCR 100% and 100%. The positive and negative predictive values of the physical exam findings were: BCR 100% and 100%, rectal tone 31% and 98%, PVR 21% and 96%, and perianal sensation 13% and 96%. Two FFTs utilizing a combination of BCR, voluntary rectal tone and perianal sensation, resulted in no false negatives. The first used BCR followed by rectal tone and perianal sensation, while the second used rectal tone followed by perianal sensation and BCR. CONCLUSIONS The results of this study highlighted that BCR was highly accurate in diagnosing and ruling out CES. However, because not all patients underwent a BCR examination, we utilized FFTs to demonstrate that a combination of BCR with other physical examinations can effectively rule out or rule in CES. Our analysis produced two FFTs that resulted in no missed diagnoses of CES. This study suggests that MRI may be unnecessary to rule out CES in patients with negative physical exam findings. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.