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 cellrelated 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

(Left) 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. (Right) 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.

(Left) Axial FLAIR MR in an

older adult with small cell lung

cancer and subacute dementia

shows striking hyperintensity

in the right insula ﬇. (Right)

Coronal T2WI in the same

patient shows abnormal

hyperintensity in both medial

temporal lobes ſt 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.

Cysts, and Disorders

Brain: Pathology-Based Diagnoses: Neoplasms,

153