Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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October 29, 2020
Acute Necrotizing Encephalopathy (ANE) Triggered by Influenza
- Background:
- ANE is a rapidly progressive, underrecognized cause of acute encephalopathy.
- Triggered by a viral illness, particularly influenza, HHV-6, HSV, and mycoplasma; has been described in patients with COVID-19
- Recurrent cases are associated with mutations in RANBP2, which encodes the nuclear pore protein.
- The pathologic process is immune-mediated with “cytokine storm,” edema, necrosis, and petechial hemorrhage.
- Clinical Presentation:
- The classical presentation is acute disturbance of consciousness over hours, associated neurologic deficits, and sometimes seizures.
- Inflammatory markers and transaminases are often raised.
- Excellent recovery is possible (as with this patient, when recognized and treated early), but there is a 30% mortality risk and a 90% risk of neurologic sequelae.
- Key Diagnostic Features:
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Dynamic process (occurring over hours, days, and weeks) with a symmetric distribution with thalamic predilection showing predominantly T1 hypointensity, T2 hyperintensity, and restricted diffusion
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Evolution to a concentric/laminar pattern of signal in the thalami on ADC due to central hemorrhage/necrosis, which may progress to central cavitation
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Often accompanied by bilateral lesions in the cerebral white matter, putamen, brain stem tegmentum, and dentate nuclei
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Various patterns of enhancement
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- Differential Diagnoses:
- Clinical, radiologic, and biochemical characteristics of ANE are usually distinctive. When lesions or the clinical context is atypical, consider alternative thalamic pathology.
- ADEM lesions are often asymmetric and more diffusely affect white matter.
- Bilateral thalamic infarcts (eg, artery of Percheron or venous): If other risk factors or lacking ANE criteria, consider early MRV and MRA
- Infiltrative lesions (eg, bilateral thalamic glioma): Usually homogeneous with normal diffusion, but high-grade lesions may differ; MRS choline peak
- Acute encephalitis (eg, Japanese encephalitis/flavivirus): Endemic area; inflammatory cells in CSF (compared with ANE); specific viral testing
- Hypoxic/ischemic: Usually accompanied by a circulatory/hypoxic episode and clinical course
- Neurometabolic disorders/inborn errors: Biochemistry and “metabolic” and genetic screens; more often infantile presentations
- Toxic encephalopathy/other systemic disorders: Often context-specific and slightly different neuroimaging patterns (eg, B1 deficiency/drugs/Reye syndrome [in Reye syndrome, often diffuse cerebral edema with hyperammonemia, hypoglycemia, and lactic acidosis])
- Treatment:
- Supportive and anecdotal treatments: trial of immunotherapy (eg, corticosteroids, IVIG), early hypothermia, antiviral agents, anticonvulsants
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