MR Imaging of Acute Cerebellar Involvement in Pediatric Anti-N-Methyl-D-Aspartate Receptor Encephalitis

Case Description

A 4-year-old boy presented with 10 days of fever, autonomical instability, confusion, sleeplessness, unstable gait, and choreoathetoid limb movements. Laboratory tests revealed leukocytosis and rhabdomyolysis. Brain magnetic resonance imaging (MRI) 3 days after admission was normal, but repeat MRI at 7 days revealed findings compatible with cerebellitis ([Fig. 1]). Cerebrospinal fluid (CSF) studies showed lymphocytic pleocytosis and positive anti-N-methyl-D-aspartate (NMDA) receptor antibodies. Whole-body fluorine-18 fluorodeoxyglucose positron emission tomography showed diffuse bilateral cerebellar and occipital lobe hypometabolism ([Fig. 2]), but no evidence of an occult malignancy. Electroencephalography showed diffuse high-voltage background slowing (2–5 Hz) with independent, bilateral high-voltage sharp waves predominantly in the frontal regions. Intravenous immunoglobulin and high-dose methylprednisolone were started; however, repeat lumbar puncture showed persistent CSF pleocytosis. Rituximab was started approximately 4 weeks after admission and administered in 4 weekly doses. Three months after admission, the child had severe neurological sequelae including residual choreiform movements and dysphagia requiring a gastrostomy tube.

Fig. 1 Brain magnetic resonance imaging performed 7 days after hospital admission. (A) Axial T2-weighted image shows diffuse hyperintense signal in the cerebellar cortex and to a lesser extent in the dentate nuclei. (B) Axial diffusion-weighted image (DWI) shows increased signal in the cerebellar cortex bilaterally, more pronounced on the right. (C) Axial apparent diffusion coefficient map shows hypointense signal in the areas of DWI abnormality, confirming that they represent restricted diffusion.

Fig. 2 Axial fluorine-18 fluorodeoxyglucose positron emission tomography image demonstrates symmetric bilateral cerebellar hypometabolism. The occipital lobes were similarly involved (not shown).

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