Paraneoplastic Syndromes
Paraneoplastic Neurological Syndromes
What Do You Need to Know?
- Two antibody classes: Cell-surface antibodies are directly pathogenic and immunotherapy-responsive; intracellular (onconeural) antibodies are biomarkers of T-cell–mediated neuronal destruction — poor immunotherapy response, treat the tumor
- 2021 PNS-Care score: Classifies antibodies as high-risk (definite paraneoplastic), intermediate-risk, or low-risk — guides cancer screening intensity
- Anti-Yo = paraneoplastic cerebellar degeneration: Most common cause of PCD; ovarian/breast cancer; irreversible Purkinje cell loss; poor prognosis despite treatment
- Anti-Hu = sensory neuropathy/encephalomyelitis: SCLC; dorsal root ganglionopathy with painful asymmetric sensory ataxia; poor prognosis
- Tumor removal is primary therapy: Especially for intracellular antibody syndromes where immunotherapy alone is insufficient
- Negative cancer screen does NOT exclude malignancy: Repeat imaging q3–6 months for ≥2 years; tumors may be occult or microscopic
- Early treatment is critical: Cell-surface antibody syndromes are reversible if caught early; intracellular antibody syndromes cause irreversible damage before diagnosis
Classification: Cell-Surface vs. Intracellular Antibodies
Fundamental Distinction
| Feature | Cell-Surface Antibodies | Intracellular (Onconeural) Antibodies |
|---|---|---|
| Targets | NMDA-R, LGI1, CASPR2, AMPA-R, GABA-B, DPPX | Hu (ANNA-1), Yo (PCA-1), Ri (ANNA-2), CV2/CRMP5, Ma2, amphiphysin, SOX1 |
| Pathogenic mechanism | Directly pathogenic — receptor internalization, blockade, or complement-mediated damage | Antibodies are biomarkers only — CD8+ T-cell–mediated cytotoxicity causes neuronal death |
| Immunotherapy response | Often excellent — reversible neuronal dysfunction | Usually poor — irreversible neuronal destruction precedes diagnosis |
| Cancer association | Variable (NMDA-R: ovarian teratoma; GABA-B: SCLC ~50%; LGI1: rarely paraneoplastic) | Strongly paraneoplastic — most have underlying malignancy (>80% for Hu, Yo) |
| Primary treatment | Immunotherapy (steroids, IVIg, PLEX, rituximab) | Tumor removal — immunotherapy is adjunctive |
| Prognosis | Generally favorable with early treatment | Guarded to poor — neurological deficits often permanent |
💎 Board Pearl
- Cell-surface = treatable; intracellular = find the tumor. This is the single most important distinction in paraneoplastic neurology. Cell-surface antibodies cause reversible receptor dysfunction; intracellular antibodies mark irreversible T-cell–mediated neuronal death
2021 PNS-Care Score
- Developed to standardize diagnosis and cancer screening in suspected paraneoplastic syndromes
- Combines antibody risk level + clinical phenotype + cancer presence
| Antibody Risk Level | Examples | Cancer Association |
|---|---|---|
| High-risk | Hu (ANNA-1), Yo (PCA-1), Ri (ANNA-2), CV2/CRMP5, amphiphysin, Ma2, SOX1 | >70% have cancer; intensive screening mandatory |
| Intermediate-risk | NMDA-R, AMPA-R, GABA-B, CASPR2, DPPX | Variable (20–50%); cancer screening required |
| Low-risk | LGI1, GABA-A, GAD65, GlyR | <5–10%; cancer screening recommended but low yield |
PNS-Care Diagnostic Levels
- Definite PNS: High-risk antibody + classic syndrome ± cancer
- Probable PNS: High-risk antibody + non-classic syndrome, OR intermediate-risk antibody + cancer
- Possible PNS: Classic syndrome without antibody; or intermediate-risk antibody without cancer
Intracellular (Onconeural) Antibodies
Master Table: Intracellular Antibodies, Cancers & Syndromes
| Antibody | Synonym | Cancer | Key Neurological Syndromes | High-Yield Notes |
|---|---|---|---|---|
| Anti-Hu | ANNA-1 | SCLC (>80%) | Sensory neuropathy (dorsal root ganglionopathy); encephalomyelitis; limbic encephalitis | Most common intracellular antibody; sensory neuropathy is the classic presentation |
| Anti-Yo | PCA-1 | Ovarian, breast | Paraneoplastic cerebellar degeneration (PCD) | Most common cause of PCD; irreversible Purkinje cell loss; typically women |
| Anti-Ri | ANNA-2 | Breast, SCLC | Opsoclonus-myoclonus syndrome (OMS); brainstem encephalitis | OMS in adults — think anti-Ri; may also have jaw dystonia |
| Anti-CV2/CRMP5 | — | SCLC, thymoma | Chorea; optic neuritis; peripheral neuropathy; encephalitis | Diverse phenotype; optic neuritis + chorea combination is suggestive |
| Anti-Ma2 | Anti-Ta | Testicular germ cell (<50 yr); lung (>50 yr) | Limbic encephalitis; diencephalic encephalitis; narcolepsy-like hypersomnia; vertical gaze palsy | Young male + limbic encephalitis = testicular ultrasound; hypothalamic/brainstem involvement |
| Anti-amphiphysin | — | Breast, SCLC | Stiff-person syndrome (paraneoplastic form) | Amphiphysin = paraneoplastic SPS; distinguish from GAD65 SPS (non-paraneoplastic) |
| Anti-SOX1 | — | SCLC | Lambert-Eaton myasthenic syndrome; cerebellar degeneration | Often coexists with anti-VGCC; supports SCLC screening in LEMS |
💎 Board Pearl
- Anti-Hu = SCLC + sensory neuropathy. The most tested association. Subacute asymmetric painful sensory ataxia (dorsal root ganglionopathy) in a smoker = check anti-Hu + CT chest
- Anti-Yo = ovarian/breast + cerebellar degeneration. Woman with subacute pancerebellar syndrome → anti-Yo + pelvic imaging
- Anti-Ma2 + young man = testicular germ cell tumor. Limbic/diencephalic encephalitis with hypersomnia or vertical gaze palsy in a male <50 yr → testicular ultrasound is mandatory
Cell-Surface Antibodies (Overlap with Autoimmune Encephalitis)
Cell-Surface Antibodies: Paraneoplastic Associations
| Antibody | Target | Cancer Association | Key Syndrome | High-Yield Notes |
|---|---|---|---|---|
| Anti-NMDAR | NR1 subunit | Ovarian teratoma (20–50% in women) | Anti-NMDAR encephalitis: psychiatric → seizures → dyskinesias → autonomic instability → coma | Most common autoimmune encephalitis; extreme delta brush on EEG; pelvic imaging in all women |
| Anti-LGI1 | LGI1 protein | Rarely paraneoplastic (<5%); thymoma rare | Limbic encephalitis; FBDS; hyponatremia | Low cancer risk; primarily autoimmune, not paraneoplastic |
| Anti-CASPR2 | CASPR2 protein | Thymoma (20–40%) | Morvan syndrome (insomnia + neuromyotonia + encephalopathy + autonomic); limbic encephalitis | Older males; CT chest for thymoma |
| Anti-AMPAR | GluA1/GluA2 | SCLC, breast, thymoma (~70%) | Limbic encephalitis with relapsing course | High cancer association; relapsing phenotype is characteristic |
| Anti-GABA-B | GABA-B receptor | SCLC (~50%) | Limbic encephalitis; early refractory seizures; status epilepticus | Half are paraneoplastic (SCLC); seizures often prominent |
| Anti-DPPX | DPP6 protein | Rare (<10%); B-cell lymphoma | Encephalitis with prominent GI symptoms (diarrhea, weight loss); hyperekplexia; myoclonus | Prodromal diarrhea + encephalopathy = think DPPX |
Clinical Pearl
- Cell-surface antibodies overlap with autoimmune encephalitis and are covered in more detail in that section. In the paraneoplastic context, always perform cancer screening, especially for anti-AMPAR (~70% paraneoplastic), anti-GABA-B (~50%), and anti-CASPR2 (20–40% thymoma)
Paraneoplastic Cerebellar Degeneration (PCD)
Overview
- Definition: Subacute pancerebellar syndrome developing over days to weeks in the setting of a systemic malignancy
- Mechanism: Immune-mediated irreversible Purkinje cell destruction
- Neurological symptoms often precede cancer diagnosis by months to years
Antibodies Associated with PCD
| Antibody | Cancer | Key Features |
|---|---|---|
| Anti-Yo (PCA-1) | Ovarian, breast | Most common cause of PCD; almost exclusively women; worst prognosis |
| Anti-Hu (ANNA-1) | SCLC | PCD + encephalomyelitis + sensory neuropathy (multifocal phenotype) |
| Anti-Tr/DNER | Hodgkin lymphoma | Young patients; may respond better to chemotherapy than other PCD causes |
| Anti-VGCC | SCLC | PCD + Lambert-Eaton overlap — cerebellar syndrome with LEMS features |
| Anti-mGluR1 | Hodgkin lymphoma | Rare; cell-surface target → potentially better immunotherapy response |
Clinical Features
- Subacute onset (days to weeks) of progressive pancerebellar dysfunction
- Truncal and appendicular ataxia, dysarthria, nystagmus (downbeat common), dysphagia
- Rapidly disabling — many patients wheelchair-bound within weeks
- May stabilize but rarely improves once established (damage is done)
Diagnosis
- MRI: Initially normal → progressive cerebellar atrophy over weeks to months
- CSF: Lymphocytic pleocytosis, elevated protein, oligoclonal bands (early); may normalize later
- Antibody testing: Anti-Yo, anti-Hu, anti-Tr/DNER, anti-VGCC panel
- PET-CT: Most sensitive for occult malignancy; may show cerebellar hypermetabolism early
Treatment & Prognosis
- Tumor treatment is the most effective intervention — may stabilize progression
- Immunotherapy (steroids, IVIg, PLEX, rituximab) — generally poor response for intracellular antibody PCD
- Exception: Anti-Tr/DNER (Hodgkin) and anti-VGCC PCD may respond better
- Prognosis is poor — most patients have permanent severe cerebellar disability
💎 Board Pearl
- Subacute cerebellar syndrome + normal MRI + middle-aged woman = anti-Yo PCD until proven otherwise. Order anti-Yo antibodies and pelvic/breast imaging simultaneously. MRI is often normal early — cerebellar atrophy develops later
- PCD + LEMS = anti-VGCC + SCLC. If cerebellar ataxia coexists with proximal weakness, areflexia, and autonomic dysfunction, test for anti-VGCC and screen for SCLC
Opsoclonus-Myoclonus Syndrome (OMS)
Overview
- Definition: Involuntary, chaotic, conjugate, multidirectional saccades (opsoclonus) + myoclonus + cerebellar ataxia
- Also called “dancing eyes–dancing feet” syndrome
- May include cognitive/behavioral changes and sleep disturbance
Etiology by Age
| Population | Cancer | Antibody | Key Features |
|---|---|---|---|
| Children (6 mo–3 yr) | Neuroblastoma (~50%) | Often antibody-negative | Better prognosis; responds to immunotherapy + tumor resection; long-term neurocognitive sequelae common |
| Adults | Breast cancer, SCLC | Anti-Ri (ANNA-2) | Poorer prognosis; less responsive to immunotherapy than pediatric OMS |
Diagnosis & Treatment
- Children: Abdominal/chest imaging for neuroblastoma; urine catecholamines (VMA, HVA); MIBG scan
- Adults: Anti-Ri antibodies; CT chest/abdomen/pelvis; mammography
- Treatment: Tumor resection + immunotherapy (ACTH/steroids, IVIg, rituximab); children respond better than adults
💎 Board Pearl
- Opsoclonus-myoclonus in a child = neuroblastoma screening. Paradoxically, children with neuroblastoma + OMS have better tumor prognosis (often differentiated, favorable biology) but worse neurological outcomes (chronic cognitive impairment)
- Adult OMS + anti-Ri = breast cancer or SCLC. Anti-Ri (ANNA-2) is the key antibody in adult paraneoplastic OMS
Paraneoplastic Sensory Neuropathy & Encephalomyelitis
Anti-Hu (ANNA-1) Syndrome
- Cancer: SCLC (>80%); the prototypical paraneoplastic syndrome
- Mechanism: T-cell–mediated destruction of dorsal root ganglion neurons (ganglionopathy)
Sensory Neuropathy (Dorsal Root Ganglionopathy)
- Subacute onset over weeks to months; asymmetric, multifocal
- Predominantly large-fiber loss: proprioceptive loss → sensory ataxia (positive Romberg, pseudoathetosis)
- Painful — neuropathic pain often prominent and disabling
- Upper and lower limbs; may be asymmetric or patchy early, then widespread
- Distinguishing feature: non-length-dependent pattern (proximal/facial involvement possible) vs. typical length-dependent polyneuropathy
Encephalomyelitis
- May coexist with or progress from sensory neuropathy
- Multi-level involvement: limbic encephalitis + brainstem encephalitis + myelitis + sensory neuropathy
- Reflects widespread T-cell attack on neurons throughout the neuroaxis
Diagnosis
- Nerve conduction studies: Asymmetric sensory nerve action potential (SNAP) loss with preserved motor studies; non-length-dependent pattern
- Anti-Hu (ANNA-1): Serum and CSF testing
- CT chest: SCLC screening — mandatory in any patient with anti-Hu
- CSF: Lymphocytic pleocytosis, elevated protein, oligoclonal bands
Prognosis
- Poor — irreversible neuronal loss; most patients develop progressive disability
- Immunotherapy minimally effective once symptoms established
- Tumor treatment may stabilize but rarely reverses deficits
💎 Board Pearl
- Asymmetric sensory ataxia + non-length-dependent SNAP loss + smoker = anti-Hu ganglionopathy + SCLC. This is the classic board-tested pattern. The non-length-dependent pattern (proximal > distal or patchy) distinguishes ganglionopathy from typical polyneuropathy
- Dorsal root ganglionopathy causes: Paraneoplastic (anti-Hu), Sjögren syndrome, cisplatin toxicity, pyridoxine toxicity (B6), idiopathic
Lambert-Eaton Overlap
Paraneoplastic LEMS (Brief — See NMJ Section for Full Details)
- Antibody: Anti-VGCC (P/Q-type voltage-gated calcium channels)
- Cancer: SCLC in ~60% of LEMS cases (paraneoplastic LEMS); 40% are autoimmune without cancer
- Mechanism: Presynaptic NMJ — antibodies reduce calcium influx → decreased ACh release
- Clinical triad: Proximal weakness (legs > arms) + areflexia (with post-exercise facilitation) + autonomic dysfunction (dry mouth, constipation, erectile dysfunction)
- EMG: Low CMAP amplitude; ≥100% increment with high-frequency RNS (20–50 Hz) or post-exercise facilitation
- DELTA score: Predicts cancer risk in LEMS (Dysarthria/dysphagia, Erectile dysfunction, Loss of weight, Tobacco use, Age ≥50); score ≥3 = high cancer risk
- Anti-SOX1: If positive with VGCC, further supports paraneoplastic etiology (SCLC)
💎 Board Pearl
- LEMS + SOX1 + VGCC = SCLC. Anti-SOX1 with anti-VGCC greatly increases specificity for paraneoplastic LEMS
- Post-exercise facilitation on exam + increment ≥100% on RNS = LEMS. The opposite of myasthenia gravis (which has decrement with RNS)
Stiff-Person Syndrome (SPS)
Two Antibody Subtypes
| Feature | Anti-GAD65 SPS | Anti-Amphiphysin SPS |
|---|---|---|
| Antibody | GAD65 (high titers ≥20 nmol/L) | Amphiphysin |
| Paraneoplastic? | No — autoimmune | Yes — breast cancer, SCLC |
| Associated conditions | Type 1 diabetes, autoimmune thyroiditis, pernicious anemia | Underlying malignancy (>80%) |
| Demographics | Women > men; 30–60 yr | Women (breast cancer); older age |
| Treatment priority | Symptomatic + immunotherapy | Tumor removal + symptomatic + immunotherapy |
Clinical Features
- Continuous muscle stiffness — axial muscles (paraspinal, abdominal) > proximal limbs
- Episodic spasms triggered by startle, emotional stress, or sudden movement
- Exaggerated lumbar lordosis from paraspinal rigidity
- Task-specific phobia (fear of falling due to spasms) — often misdiagnosed as psychiatric
- Variants: Stiff-limb syndrome (focal); progressive encephalomyelitis with rigidity and myoclonus (PERM — severe, anti-GlyR)
Diagnosis
- EMG: Continuous motor unit activity in agonist and antagonist muscles simultaneously; activity resolves with benzodiazepines (diazepam test)
- Anti-GAD65: High titers (≥20 nmol/L); low titers nonspecific (seen in diabetes)
- Anti-amphiphysin: If positive → cancer screening mandatory
Treatment
- Symptomatic: Benzodiazepines (diazepam, clonazepam — first-line); baclofen (oral or intrathecal)
- Immunotherapy: IVIg (best evidence — RCT proven); PLEX; rituximab for refractory cases
- Tumor removal for amphiphysin-positive paraneoplastic SPS
💎 Board Pearl
- GAD65 SPS = autoimmune + diabetes association. Amphiphysin SPS = paraneoplastic + cancer screening mandatory. This is the key distinction on boards
- EMG finding: continuous motor unit activity in agonist and antagonist muscles simultaneously — pathognomonic for SPS; abolished by diazepam
- Low GAD65 titers (<20 nmol/L) are NOT diagnostic — found in ~5–8% of the general population (especially type 1 diabetes)
Cancer Screening in Paraneoplastic Syndromes
Initial Workup
| Test | Indication | Key Targets |
|---|---|---|
| CT chest/abdomen/pelvis | All patients with suspected PNS | SCLC, ovarian tumors, thymoma, breast cancer |
| PET-CT (whole body) | CT negative but high clinical suspicion; high-risk antibody | Higher sensitivity for small/occult tumors; lymphoma |
| Pelvic MRI/ultrasound | Women with anti-NMDAR, anti-Yo | Ovarian teratoma, ovarian carcinoma |
| Testicular ultrasound | Men <50 yr with anti-Ma2 | Testicular germ cell tumor |
| Mammography/breast MRI | Anti-Ri, anti-amphiphysin, anti-Yo | Breast carcinoma |
Follow-Up Screening
- Negative initial screen does NOT exclude malignancy
- Tumors may be occult, microscopic, or slowly growing
- Repeat imaging every 3–6 months for ≥2 years (high-risk antibodies)
- PET-CT recommended for follow-up if initial CT negative
- Some antibodies (anti-Hu, anti-Yo) are found ≥80% of the time with cancer — persistence of search is essential
💎 Board Pearl
- Negative cancer screen + high-risk antibody = keep looking. Repeat imaging q3–6 months for at least 2 years. The neurological syndrome may precede detectable cancer by months to years
- Antibody-specific screening: Anti-Yo → pelvic + breast imaging. Anti-Ma2 in young male → testicular ultrasound. Anti-Hu → CT chest for SCLC. Anti-Ri → mammography + CT chest
Treatment Principles
Hierarchy of Treatment
- 1. Tumor removal/treatment: The single most important intervention — removes the antigenic stimulus driving the immune response
- 2. First-line immunotherapy: IV methylprednisolone (1 g/day × 5 days); IVIg (0.4 g/kg/day × 5 days); PLEX (5–7 exchanges)
- 3. Second-line immunotherapy: Rituximab (375 mg/m2 weekly × 4); cyclophosphamide (IV pulse monthly)
- 4. Supportive care: Physical/occupational therapy, symptom management, pain control
Response by Antibody Type
| Antibody Type | Immunotherapy Response | Rationale |
|---|---|---|
| Cell-surface antibodies | Good to excellent | Antibody-mediated receptor dysfunction is reversible; removing antibodies restores receptor function |
| Intracellular antibodies | Poor | Neuronal destruction by T-cells is irreversible by the time of diagnosis; antibodies are bystanders |
Key Treatment Principles
- Early treatment is critical — especially for cell-surface antibody syndromes where neuronal dysfunction is still reversible
- For intracellular antibody syndromes: tumor treatment > immunotherapy
- Immunotherapy may stabilize (prevent further decline) even if it cannot reverse existing damage
- Long-term immunosuppression (rituximab, mycophenolate) may be needed for relapsing cell-surface antibody syndromes
- Monitor for treatment complications: infections (rituximab), metabolic effects (steroids), renal toxicity (cyclophosphamide)
Clinical Pearl
- Do not delay immunotherapy while awaiting tumor identification in rapidly progressive syndromes. Simultaneous cancer workup and immunotherapy initiation is standard of care. For cell-surface antibody syndromes, the window for reversibility may be narrow
Summary: Antibody–Cancer–Syndrome Quick Reference
High-Yield Associations for Board Review
| Syndrome | Antibody | Cancer | Key Clue |
|---|---|---|---|
| Cerebellar degeneration | Anti-Yo | Ovarian, breast | Woman + subacute ataxia + normal MRI |
| Sensory neuropathy | Anti-Hu | SCLC | Asymmetric painful sensory ataxia + smoker |
| Opsoclonus-myoclonus (adults) | Anti-Ri | Breast, SCLC | “Dancing eyes–dancing feet” |
| Opsoclonus-myoclonus (children) | Often negative | Neuroblastoma | Child + chaotic eye movements |
| Limbic/diencephalic encephalitis | Anti-Ma2 | Testicular (young), lung (old) | Young male + hypersomnia + vertical gaze palsy |
| Chorea + optic neuritis | Anti-CV2/CRMP5 | SCLC, thymoma | Diverse phenotype; chorea + optic neuritis |
| Stiff-person (paraneoplastic) | Anti-amphiphysin | Breast, SCLC | SPS + cancer = amphiphysin (not GAD65) |
| Stiff-person (autoimmune) | Anti-GAD65 | None (autoimmune) | SPS + diabetes + no cancer |
| Lambert-Eaton | Anti-VGCC (± SOX1) | SCLC (~60%) | Proximal weakness + areflexia + autonomic + facilitation |
| Encephalitis (anti-NMDAR) | Anti-NMDAR | Ovarian teratoma | Young woman + psychiatric → seizures → dyskinesias |
💎 Board Pearl
- Mnemonic: “Yo-Ovary, Hu-Lung, Ri-Breast, Ma-Testis” — remember the antibody-cancer pairs for rapid recall
- Paraneoplastic syndrome precedes cancer diagnosis in the majority of cases — a new neurological syndrome may be the first sign of an occult malignancy
- Two exceptions where paraneoplastic syndromes may respond to immunotherapy: Anti-Tr/DNER (Hodgkin PCD) and anti-VGCC (LEMS) — because they target cell-surface or extracellular antigens
References
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