False-Negative Initial Magnetic Resonance Imaging in Acute Posterior Circulation Stroke: A Case Report Describing Locked in Syndrome

Abstract

SESSION TITLE: Student/Resident Case Report Poster - Critical Care II SESSION TYPE: Student/Resident Case Report Poster PRESENTED ON: Tuesday, October 25, 2016 at 01:30 PM - 02:30 PM INTRODUCTION: As identification of acute stroke is greatly dependent on neuroimaging, negative CT and MRI in the context of focal neurological deficits demands heightened awareness of technology limitations. It has been described in the literature that posterior circulation strokes may not be readily seen on MRI for up to 24 hours. We present a case of Locked in Syndrome whose initial presentation was bilateral lower extremity weakness and dysarthria with negative MRI findings. CASE PRESENTATION: Patient is a 49 yo male with past medical history significant for HTN, DM, CHF, presenting with two days of dysarthria and bilateral lower extremity weakness resulting in a fall on day of admission. On physical exam, cranial nerves two through twelve were intact, cerebellar signs negative, sensory was intact bilaterally upper and lower extremities. Patient was admitted for stroke work up with an NIHSS of 5. CT brain and MRI showed no acute pathology. Over the next 4 days, patient developed worsening flaccid quadraplegia with bulbar symptoms. Repeat MRI on day 5 of admission showed bilateral basilar pontine infarcts on diffusion weighted imaging (DWI) not previously seen. NIHSS progressed to 12 and on day five, patient required intubation for airway protection. Exam at this time included quadraplegia and complete anarthria, with preservation of eye movement. After an extended period in the critical care unit, patient was discharged to a rehabilitation center. DISCUSSION: Imaging on presentation, localizes the foci of infarction in a vast majority of patients. It is important to remember that while DWI has become synonymous with the acute inpatient management of stroke, reported sensitivity in ischemic stroke ranges from 90 to 98% depending on stroke location and timing of the study. False negative diffusion weighted imaging is especially prevalent in patients with posterior circulation and lacunar strokes. In our case, initial imaging findings obfuscated the diagnosis. Only after clinical deterioration and repeat neuroimaging was the diagnosis made. CONCLUSIONS: Considering the high morbidity and mortality of disease, a physician’s index of suspicion for posterior circulation or hyper-acute infarctions should be raised in patients with a correlating clinical exam and negative initial neuroimaging findings. There is evidence in the literature that clinical examination may be more sensitive than MRI in detecting posterior circulation strokes. Because natural infarct evolution is to be expected, repeat neuroimaging may be necessary. Reference #1: Ay H, et al. Normal diffusion-weighted MRI during stroke-like deficits. Neurology. 1999 Reference #2: Oppenheim C, et al. False-negative diffusion-weighted MR findings in acute ischemic stroke. AJNR Am J Neuroradiol. 2000 Reference #3: Chalela JA, et al. Magnetic resonance imaging and computed tomography in emergency assessment of patients with suspected acute stroke: a prospective comparison. Lancet. 2007 DISCLOSURE: The following authors have nothing to disclose: Christian Castaneda, Michael Lerario No Product/Research Disclosure Information