Perfusion Imaging in Autoimmune Encephalitis

Abstract

Encephalitis is characterized by inflammation of brain tissue and has various infectious and noninfectious causes. CSF analysis and MRI usually reveal inflammatory changes although sometimes brain imaging may be normal. Autoimmune encephalitis is caused by antibodies against neuronal synaptic receptors, surface proteins, or intracellular proteins. In this case report, we present a 65-year-old female who presented with a fall and altered mental status. Workup for infectious etiologies was negative and MRI of the brain displayed focal restricted diffusion with corresponding T2-FLAIR hyperintensity involving gray matter structures, making the diagnosis unclear. CT perfusion of the brain demonstrated increased cerebral blood volume and cerebral blood flow in the left parietooccipital gray matter, with corresponding normal mean transit time. Following treatment failure with acyclovir, antibiotics, and steroids, the patient was found to be positive for GAD65 antibodies and diagnosed with autoimmune encephalitis. Symptoms markedly improved with plasmapheresis. Autoimmune encephalitis rarely causes restricted diffusion and this is the first case report to describe corresponding hyperperfusion on CT perfusion study.

Figure 1

64-year-old female with confusion, right lower extremity weakness, and questionable encephalitis. Axial FLAIR MR image (a) shows increased signal intensity and gyriform swelling in the cortex and subcortical white matter of the left parietooccipital lobe and a focus in the left thalamus. Diffusion weighed (b) and attenuation diffusion coefficient, ADC, MR images (c) reveal mild decreased diffusivity. No susceptibility artifact or contrast enhancement is observed on axial susceptibility weighted image, SWI (d), and axial T1 weighted (e) and axial T1 weighted postgadolinium images (f), respectively.

Figure 2

CT perfusion was performed 10 days after the initial MRI imaging. The postprocessed CT perfusion maps in axial plane at the level of the left parietooccipital cortical abnormality reveal increased cerebral blood flow (CBF) and cerebral blood volume (CBV) in the affected cortex on the left as compared to the normal brain parenchyma on the right. The time to peak (TTP) is decreased.