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Paraneoplastic Syndromes and Limbic Encephalitis


KEY FACTS

Terminology

  • Remote neurological effects of cancer, associated with extra-CNS tumors

    • Most common tumor: Small cell lung carcinoma

  • Limbic encephalitis (LE) is most common clinical paraneoplastic syndrome

Imaging

  • Limbic encephalitis: Hyperintensity in mesial temporal lobes, limbic system

    • Mimics herpes encephalitis but subacute/chronic

  • Paraneoplastic cerebellar degeneration (PCD): Cerebellar atrophy

  • Brainstem encephalitis: T2 hyperintensity in midbrain, pons, cerebellar peduncles, basal ganglia

  • Most paraneoplastic syndromes do not have associated imaging findings

Top Differential Diagnoses

  • Herpes encephalitis

  • Low-grade (grade II) diffuse astrocytoma

  • Status epilepticus

  • Gliomatosis cerebri

Clinical Issues

  • < 1% of patients with systemic cancers develop paraneoplastic syndrome

  • Immune mediated by autoantibodies or cytotoxic T cell-related mechanisms

    • 60% have circulating serum autoantibodies

  • LE: Memory loss, cognitive dysfunction, dementia, psychological features, seizures

  • PCD: Ataxia, incoordination, dysarthria, nystagmus

  • Brainstem encephalitis: Brainstem dysfunction including cranial nerve palsies, visual changes

  • Treatment of primary tumor may improve symptoms

Axial FLAIR MR shows abnormal hyperintensity in the bilateral medial temporal lobes
, characteristic of limbic encephalitis, the most common paraneoplastic syndrome. Bilateral involvement is typical of limbic encephalitis.

Axial T1WI C+ MR in the same patient shows no significant enhancement in the medial temporal lobes. Enhancement is often present in limbic encephalitis. The patient's symptoms often improve after treatment of the primary tumor.

Axial FLAIR MR in an older adult with small cell lung cancer and subacute dementia shows striking hyperintensity in the right insula
.

Coronal T2WI in the same patient shows abnormal hyperintensity in both medial temporal lobes
and right insular cortex
. Imaging of limbic encephalitis mimics that of herpes encephalitis; however, patients with limbic encephalitis have a subacute presentation. Hemorrhage suggests herpes rather than limbic encephalitis.

TERMINOLOGY

Synonyms

  • Paraneoplastic syndromes (PS), paraneoplastic disease

Definitions

  • Remote neurological effects of cancer, associated with extra-CNS tumors

    • Most common tumor: Small cell lung carcinoma

  • Limbic encephalitis (LE) is most common clinical paraneoplastic syndrome

    • Only PS with clearly defined imaging features

IMAGING

General Features

  • Best diagnostic clue

    • Limbic encephalitis: Hyperintensity in mesial temporal lobes, limbic system

      • –

        Looks like herpes encephalitis but different clinical course (subacute vs. chronic)

    • Initial study normal in 20-40%

    • Most paraneoplastic syndromes do not have associated imaging findings

  • Location of LE: Hippocampus, amygdala, cingulate gyrus, pyriform cortex, subfrontal cortex, insula

CT Findings

  • NECT: Initial CT scan normal in > 95%

    • Rare: Low density within mesial temporal lobes

  • CECT: Usually no visible enhancement

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