Paraneoplastic Neurologic Syndromes and Autoimmune Encephalitis¶
Chapter 99 | Part 4: Oncology and Hematology
KEY CLINICAL POINTS¶
- High-risk antibodies (e.g., Anti-Hu, Anti-Ri, Anti-Tr) are strongly associated with specific tumors (SCLC, breast, ovarian) and have >70% probability of underlying cancer.
- Paraneoplastic syndromes are autoimmune-mediated, with antibodies targeting intracellular or cell-surface antigens, leading to neuronal dysfunction.
- Early detection of cancer is critical; imaging (MRI), CSF analysis, and antibody testing (e.g., anti-NMDAR, anti-GAD65) are essential for diagnosis.
- Treatment prioritizes tumor removal and immunotherapy (IVIg, steroids, rituximab) for antibody-mediated syndromes, while cytotoxic T-cell targeting is key for intracellular antigen-related cases.
- Prognosis varies: anti-Ma2-associated encephalitis responds to tumor and immunotherapy, while many cerebellar syndromes have poor outcomes.
1. DEFINITION & OVERVIEW¶
Paraneoplastic neurologic disorders (PNDs) are autoimmune syndromes triggered by cancer, affecting the nervous system. Autoimmune encephalitis includes antibody-mediated syndromes (e.g., anti-NMDAR, anti-GAD65) and paraneoplastic syndromes linked to tumors like SCLC, breast, or ovarian cancer. PNDs often precede cancer diagnosis by 60% of cases.
Table 99-2: High-Risk Antibodies (>70% Cancer Association)¶
| ANTIBODY | ASSOCIATED SYNDROME(S) | TUMORS |
|---|---|---|
| Anti-Hu (ANNA1) | Encephalomyelitis, sensory neuronopathy | SCLC |
| Anti-Ri (ANNA2) | Cerebellar degeneration, opsoclonus | Breast, gynecologic, SCLC |
| Anti-Tr (DNER) | Rapidly progressive cerebellar syndrome | Hodgkin’s lymphoma |
| Anti-PCA2 (MAP1B) | Sensorimotor neuropathy, cerebellar syndrome | SCLC, non-SCLC, breast cancer |
| Anti-amphiphysin | Stiff-person syndrome, encephalomyelitis | Breast, SCLC |
1.1 Pathogenesis¶
PNDs arise from immune responses to tumor-derived antigens (intracellular or cell-surface). Antibodies against intracellular antigens (e.g., Hu, Ri) trigger T-cell-mediated cytotoxicity, while surface antigens (e.g., NMDAR) cause direct antibody effects. Tumor control improves neurologic outcomes.
1.2 Classification¶
PNDs are classified by antibody risk: high-risk (>70% cancer association), intermediate (30–70%), and low (<30%). High-risk antibodies (Anti-Hu, Anti-Ri) are linked to SCLC, breast, and ovarian tumors.
2. EPIDEMIOLOGY¶
PNDs affect 0.5–1% of all cancer patients, but 2–3% of neuroblastoma/SCLC patients and 30–50% of SCLC patients. High-risk antibodies are more common in SCLC, breast, and ovarian cancers. Age and gender vary by syndrome (e.g., anti-NMDAR encephalitis in young women).
2.1 Risk Factors¶
SCLC, breast, ovarian, and germ cell tumors are most frequently associated. Neuroblastoma and lymphomas also contribute. High-risk antibodies are more common in adults, while some syndromes (e.g., opsoclonus) occur in children.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
PNDs result from immune responses to tumor antigens (intracellular or cell-surface). Antibodies against intracellular antigens (e.g., Hu, Ri) trigger T-cell-mediated damage, while surface antigens (e.g., NMDAR) cause direct neuronal dysfunction. Tumor removal and immunotherapy are critical for treatment.
Table 99-1: Classic vs. Nonclassic Paraneoplastic Syndromes¶
| CLASSIC SYNDROMES (HIGH RISK) | NONCLASSIC SYNDROMES (MODERATE/LOW RISK) |
|---|---|
| Encephalomyelitis | Brainstem encephalitis |
| Limbic encephalitis | Stiff-person syndrome |
| Cerebellar degeneration | Progressive encephalomyelitis with rigidity |
| Opsoclonus-myoclonus | Necrotizing myelopathy |
| Sensory neuronopathy | Motor neuron disease |
3.1 Antibody Mechanisms¶
High-risk antibodies (e.g., Anti-Hu) target intracellular proteins (e.g., Hu, Ri), leading to T-cell infiltration and neuronal loss. Intermediate-risk antibodies (e.g., Anti-GABAR) target cell-surface receptors, causing direct antibody-mediated effects.
4. CLINICAL FEATURES¶
Symptoms vary by syndrome: encephalitis (seizures, confusion), cerebellar ataxia, opsoclonus, stiff-person syndrome, or autonomic dysfunction. MRI shows FLAIR abnormalities in limbic encephalitis, while cerebellar syndromes may present with ataxia and nystagmus.
Table 99-3: Intermediate-Risk Antibodies (30–70% Cancer Association)¶
| ANTIBODY | SYNDROME | TUMOR TYPE |
|---|---|---|
| Anti-NMDAR | Anti-NMDAR encephalitis | Teratoma in young women |
| ANTIBODY | SYNDROME | TUMOR TYPE |
|---|---|---|
| Anti-GABAR | Limbic encephalitis with seizures | SCLC |
| Anti-mGluR5 | Autoimmune encephalitis without distinctive features | Hodgkin lymphoma |
4.1 Syndromes¶
Anti-NMDAR encephalitis: seizures, psychosis, sleep disturbances. Anti-GAD65: stiff-person syndrome, cerebellar ataxia. Anti-Ma2: limbic encephalitis, cataplexy. Anti-LGI1: limbic encephalitis with hyponatremia.
5. DIFFERENTIAL DIAGNOSIS¶
Distinguish from viral encephalitis (e.g., HSV), autoimmune encephalitis (e.g., anti-LGI1), and idiopathic syndromes. Key features include tumor association, antibody detection, and MRI findings (e.g., limbic FLAIR abnormalities).
5.1 Viral vs. Paraneoplastic Encephalitis¶
Viral encephalitis (e.g., HSV) presents with fever and rapid onset, while paraneoplastic syndromes often have slower progression and tumor association. Anti-NMDAR encephalitis may mimic viral encephalitis but responds to immunotherapy.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic workup includes MRI (FLAIR abnormalities in limbic encephalitis), CSF analysis (pleocytosis, oligoclonal bands), and antibody testing (e.g., anti-NMDAR, anti-GAD65). Tumor imaging (CT, PET) is critical for high-risk antibodies.
Table 99-4: Low-Risk Antibodies (<30% Cancer Association)¶
| ANTIBODY | SYNDROME | TUMOR TYPE |
|---|---|---|
| Anti-LGI1 | Limbic encephalitis | Rarely thymoma |
| Anti-DPPX | Agitation, myoclonus | No cancer, but paraneoplasia |
| Anti-IgLON5 | NREM/REM sleep disorder | No tumor association |
6.1 Diagnostic Algorithms¶
- Suspect PND in patients with rapid neurologic decline and cancer history. 2. Order MRI, CSF, and antibody panels. 3. Confirm tumor with imaging (CT/PET) if antibodies are positive. 4. Use immunotherapy (IVIg, steroids) for antibody-mediated syndromes.
7. MANAGEMENT & TREATMENT¶
Treatment prioritizes tumor removal and immunotherapy. High-risk antibodies (e.g., anti-Hu) require aggressive immunosuppression (rituximab, cyclophosphamide). Anti-NMDAR encephalitis responds to IVIg, steroids, and plasma exchange. Symptomatic management includes anticonvulsants and antipsychotics.
7.1 Immunotherapy¶
First-line: IVIg, steroids, plasma exchange. Second-line: rituximab, cyclophosphamide. Anti-Ma2-associated encephalitis responds to tumor resection and immunotherapy. Anti-GAD65 syndromes may improve with immunosuppression.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies: anti-Ma2 encephalitis has ~30% response to treatment, while cerebellar syndromes (e.g., anti-CRMP5) often have poor outcomes. Complications include autonomic instability, respiratory failure, and neurologic relapses.
8.1 Long-term Outcomes¶
Early tumor detection and immunotherapy improve outcomes. Anti-NMDAR encephalitis has better prognosis than anti-GAD65 syndromes. Cerebellar degeneration is often irreversible, with residual cognitive deficits.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Avoid immunosuppressants in early pregnancy. Pediatrics: Anti-NMDAR encephalitis in children responds to immunotherapy. Elderly: Higher risk of complications from immunotherapy. Germline mutations (e.g., HLA-DRB1*10:01) may predispose to anti-IgLON5 disease.
10. KEY POINTS & CLINICAL PEARLS¶
- High-risk antibodies (Anti-Hu, Anti-Ri) are strongly linked to SCLC and ovarian cancer. 2. Anti-NMDAR encephalitis is the most common autoimmune encephalitis, often associated with teratomas. 3. Early tumor detection and immunotherapy improve outcomes. 4. MRI and CSF analysis are critical for diagnosis. 5. Symptomatic management includes anticonvulsants and antipsychotics.