Paraneoplastic Neurological Syndromes and Associated Disorders

Indications for Testing

Neurologic disease of unknown etiology without evidence of malignancy
Neurologic disease with high suspicion of malignancy or known risk factors for malignancy
- Paraneoplastic neurological syndromes (PNS) are rare
  - Initial testing should be targeted toward well-characterized antibodies

Criteria for Diagnosis

PNS can be classified based on consensus criteria (Graus et al, 2004)
- Presence or absence of tumors
- Presence of classic symptoms
- Characterization of onconeuronal antibodies

Laboratory Testing

No known malignancy – consider antibody tests based on their characterization, patient’s specific clinical manifestations (central versus peripheral nervous system; neuromuscular system), age, and sex
- Characterization of antibodies – dependent on the number of studies describing their clinical relevance as well as the nature of antibodies and their effect on the disease process
- PNS and some defined autoimmune neurologic diseases – may be confirmed by the presence of specific antibodies in the presence of clinically defined symptoms
- No antibodies present – evaluate for other disorders associated with neurological symptoms
  - Rule out metabolic disorder(s) as etiology
    - Electrolyte testing – comprehensive metabolic screening (electrolytes, BUN/creatinine, hepatic enzymes, calcium)
  - Rule out CNS infection
    - CSF studies – spinal tap with cell count, protein level, culture with gram stain; also consider immunoglobulin G (CSF) and oligoclonal bands testing
  - If above evaluations are negative – proceed with further neurologic evaluation, including EMG, muscle biopsy, CT, MRI
    - Negative neurologic testing – reevaluate in 6 months or sooner depending on symptoms
    - Positive neurologic testing – further evaluation based on test results
- In children with encephalitis of unknown origin
  - PNS is very rare – consider testing for voltage-gated potassium channel (VGKC)-complex antibodies, N-methyl-D-aspartate receptor antibody (NMDAR), and glutamic acid decarboxylase (GAD) autoantibodies
Known malignancy – antibody testing based on clinical symptoms and tumor type
- Antibodies present – PNS confirmed
  - Titers may correlate with severity of neurological symptoms
  - Correlation between response to treatment and decline in antibody titer is antibody-dependent
    - Antibodies to Hu (ANNA-1), Yo (PCCA-1), Ri (ANNA-2), CV2/CRMP5 (collapsin response mediator protein 5), Ma2/Ta (intracellular targets) may not decline with treatment
    - Neuronal surface antibodies (NSAbs) such as NMDAR may decline
      - Decline associated with positive treatment response
- Antibodies not present – evaluate for other cancer-related complications
  - CSF studies – spinal tap with cell count, protein level, culture with gram stain; also consider immunoglobulin G (CSF) and oligoclonal bands testing
    - Expected results in PNS – lymphocytic pleocytosis, increased protein concentration, change in oligoclonal bands (may be positive)
  - Electrolyte testing – comprehensive metabolic screening (electrolytes, BUN/creatinine, hepatic enzymes, calcium)
  - EMG, muscle biopsy, MRI, PET (may be the most sensitive imaging for detecting occult malignancy)

Antibody Tests to Consider

Well-characterized antineuronal (also referred to as onconeuronal) antibodies

Targets intracellular nuclear and cytoplasmic antigens
Neurologic symptoms and survival vary with both types of antibodies and tumors
- Hu, Yo, Ri, CV2/CRMP5, Ma2/Ta, amphiphysin – all considered classic and diagnostic for PNS
  - Hu, Ri, Yo – most commonly observed antibodies
  - Hu and CV2/CRMP5 – may coexist
  - Yo and Ma2/Ta – associated with specific clinical manifestations and gender specific tumors
    - Warrant customized testing based on suspected tumor
  - Amphiphysin – synaptic target with a strong association for breast cancer and treatment response

Well-characterized antibodies by clinical syndromes and associated tumors

Well-Characterized Antibodies (Target Intracellular Antigens)
Antibody	Clinical syndromes	Associated tumors
Hu	Sensory neuronopathy, encephalomyelitis, limbic encephalitis, opsoclonus-myoclonus, subacute cerebellar degeneration, autonomic neuropathy, enteric neuropathy (GI dysmotility)	Small-cell lung carcinoma (SCLC), neuroblastoma
Yo	Subacute cerebellar degeneration, occasional GI dysmotility, chorea	Ovary, breast
CV2/CRMP-5	Encephalomyelitis, chorea, limbic encephalitis, sensory neuronopathy, sensorimotor neuropathy, optic neuropathy, subacute cerebellar degeneration, autonomic neuropathy, GI dysmotility	SCLC, thymoma
Ri	Opsoclonus-myoclonus, brainstem encephalitis, cerebellar degeneration	SCLC, breast, ovary
Ma2/Ta*	Limbic/diencephalic/brainstem encephalitis, encephalomyelitis, subacute cerebellar degeneration, atypical Parkinsonism	Germ cell tumor (usually testicular), non-SCLC (male predominance)
Amphyphysin**	Stiff-person syndrome, encephalomyelitis, subacute sensory neuronopathy, sensorimotor neuropathy, limbic encephalitis	SCLC, breast, ovary
Recoverin	Cancer-associated retinopathy	SCLC, melanoma, others
Brainstem encephalitis and subacute cerebellar degeneration are usually associated with tumors other than testicular cancer. Sera from these patients also react with the Ma1 protein. *Synaptic antigenic target; associated with response to treatment

Cell surface and synaptic autoantibody targets

Antibodies target cell surface (extracellular) or synaptic antigens
Not age dependent
May or may not be associated with malignancy
Generally thought to be pathogenic
Usually treatment-responsive
NSAb syndromes – may be indistinguishable at presentation from classical PNS such as limbic encephalitis (LE)
- One or more autoantibodies can be considered in the differential based on age and sex
- NMDAR encephalitis – frequent in individuals of both genders and age groups and may mimic LE
  - Frequently non-paraneoplastic patients do respond to immunotherapy with a good chance for substantial recovery
- LGI1 (leucine-rich glioma-inactivated 1) and Caspr2 (contactin-associated protein-like 2) – previously thought to be VGKC
- Less common – AMPAR (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor) and GABA_BR (γ aminobutyric acid-B receptor), GlyR (glycine receptor), and mGluR (metabotropic glutamate receptor) antibodies

Cell surface and synaptic antibodies by clinical syndromes and associated tumors

Antibodies Against Cell Surface and Synaptic Antigens
Antibody	Clinical syndromes	Associated tumors
Extracellular Antibody Targets
VGCC P/Q type	Lambert-Eaton myasthenic syndrome, subacute cerebellar degeneration	SCLC
VGCC N type	Lambert-Eaton, sensorimotor and autonomic neuropathy	SCLC, breast
mGluR3	Rasmussen encephalitis	Non-neoplastic
AChR	Myasthenia gravis	Thymoma
nAChR
α3	Subacute autonomic neuropathy	SCLC
Muscarinic (M3)	Sjögren syndrome	Non-neoplastic
VGKC complex antibodies	Limbic encephalitis, neuromyotonia (Isaac syndrome), Morvan syndrome (limbic encephalitis and neuromyotonia), GI dysmotility, undulating myeloma, cramp-fasciculation syndrome	Thymoma, SCLC
LGI1*	Limbic encephalitis	SCLC, neuroendocrine
Caspr2*	Limbic encephalitis, Morvan syndrome	Thymoma
NMDAR (NR1)	Limbic encephalitis	Ovarian teratoma
AMPAR	Limbic encephalitis, agitation	SCLC, breast, thymoma
GABA_B R	Limbic encephalitis	SCLC
Intracellular Antibody Targets
Amphiphysin**	Stiff-person syndrome, encephalomyelitis, subacute sensory neuronopathy, sensorimotor neuropathy, limbic encephalitis	SCLC, breast, ovary
GAD	Stiff person syndrome, cerebellar degeneration, limbic encephalitis	Thymoma
VGKC-complex antibodies; may also occur independently of VGKC-complex antibodies *Synaptic antigenic target; associated with response to treatment Abbreviations: AChR = acetylcholine receptor; nAChR = nicotinic acetylcholine receptor; NMDAR = N-methyl-D-aspartate receptor; SCLC = small cell lung carcinoma; VGCC = voltage-gated calcium channel; VGKC = voltage-gated potassium channel; GluR3 = glutamate receptor type 3; GAD = glutamic acid decarboxylase; AMPAR = alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor; GABA_B R = γ-aminobutyric acid-B receptor

Partially characterized antibodies

ANNA-3, PCCA-2, PCCA-Tr, anti-glial nuclear antibody (AGNA-1, also referred to as SOX-1)
- Autoantibodies are very rare and poorly characterized
- Not recommended as first-line tests for PNS evaluation
- Unlike Hu, Ri, amphiphysin, CV2/CRMP5, and Ma2/Ta antibodies, the presence of these antibodies is not sufficient to make a diagnosis of PNS

Partially characterized antibodies by clinical syndromes and associated tumors

Partially Characterized Antibodies (Target Intracellular Antigens)
Antibody	Clinical syndromes	Associated tumors
PCCA-Tr	Subacute cerebellar degeneration	Hodgkin lymphoma
ANNA-3	Encephalomyelitis, subacute sensory neuronopathy	SCLC
PCCA-2	Encephalomyelitis, subacute cerebellar degeneration	SCLC
Zic4	Subacute cerebellar degeneration	SCLC
mGluR1	Subacute cerebellar degeneration	Hodgkin lymphoma
Anti-rod/bipolar cell	Optic neuropathy	Melanoma
AGNA-1	Lambert-Eaton myasthenic syndrome	SCLC
Abbreviations: ANNA = antineuronal nuclear antibody; mGluR1 = metabotropic glutamate receptor type 1; PCCA = Purkinje cell cytoplasmic antibody; SCLC = small-cell lung carcinoma; AGNA-1 = anti-glial nuclear antibody

Most antibodies have low positivity rates – initial testing should take these rates of positivity into account

Comprehensive panels – generally not cost effective due to low rate of positivity of less commonly observed antibodies

Onconeuronal antibody panels by component and positivity rates (based on 3 years of ARUP Laboratories’ data)

Onconeuronal Antibody Panels and Positivity Rates (based on 3 years of ARUP Laboratories’ data)
Test	Test Description	Positivity Rates
Neuronal Nuclear Antibody (ANNA) IgG by IFA with Reflex to Titer & Immunoblot, Serum	Hu and Ri are screened by immunofluorescence and confirmed by immunoblot	0.55%
Neuronal Nuclear Antibodies (ANNA) IgG, Immunoblot, Serum	Hu and Ri are confirmed by immunoblot	Hu – 3.10% Ri – 0.88%
Paraneoplastic Syndrome Antibody Panel with Reflex to ANNA Titer, PCCA Titer and Neuronal Immunoblot	ANNA abs are screened by IFA; if IFA screen is positive at 1:10, then titer and immunoblot (Hu and Ri) will be added If Purkinje cell screen is positive at 1:10, then titer and immunoblot (Yo) will be added	ANNA IFA – 0.51% PCCA IFA – 0.32%
Neuronal Antibodies (Hu, Ri, Yo, Amphiphysin) IgG by Immunoblot	Amphiphysin, Hu, Ri, and Yo are screened by immunoblot	Amphiphysin – 0.10% Hu – 0.55% Ri – 0.10% Yo – 0.38%
Purkinje Cell Cytoplasmic Antibody by IFA with Reflex to Titer & Immunoblot	If Purkinje cell screen is 1:10, then titer and immunoblot will be added	0.87%

Antibodies, PNS, and Associated Tumors

PNS and antibody association

PNS and Antibody Association
Syndrome	Most common tumor	Most-frequent antibodies
Autonomic dysfunction
GI dysmotility	SCLC	Hu, Yo, CV2/CRMP5
Neuropathy	SCLC	Hu, CV2/CRMP5, nAChR (α3)
Encephalomyelitis	SCLC	Hu, CV2/CRMP5
	Germ cell (testis)	ANNA-3, PCCA-2
	Prostate	Hu
Lambert Eaton Myasthenic Syndrome (LEMS)	SCLC	VGCC (P/Q type)
Limbic encephalitis	SCLC	Hu, CV2/CRMP5, Amphiphysin
	Germ cell (testis)	Ma2/Ta, GABA_BR, VGKC, AMPAR, Ri
	Teratoma (ovarian)	NMDAR
	Thymoma	AMPAR, GAD, VGKC
	Breast	AMPAR
Neuropathy
Subacute sensory	SCLC	Hu, CV2/CRMP5, Amphiphysin, ANNA-3
Sensorimotor	SCLC	CV2/CRMP5, Hu
Neuromyotonia	SCLC	VGKC
Opsoclonus-myoclonus	Neuroblastoma	Hu
	Breast	Ri
	SCLC	Ri
Other movement disorders
Dystonia	Teratoma (ovarian)	NMDAR
Chorea	Breast	Yo
Chorea	SCLC	CV2/CRMP-5
Parkinsonism	Germ cell (testis)	Ma2/Ta
Retinopathy	SLCC	Recoverin, CV2/CRMP5
Retinopathy	Melanoma	Anti-rod/bipolar-cell
Spinal myoclonus	Breast	Amphiphysin
Spinal myoclonus	SCLC	Amphiphysin
Stiff person syndrome	SCLC	Amphiphysin
Stiff person syndrome	Thymoma	GAD
Subacute cerebellar degeneration	Ovary, breast	Yo
	Thymoma	GAD
	SCLC	Hu, CV2/CRMP5, PCCA-2, Zic4, Ri, VGKC
	Hodgkin lymphoma	PCCA-Tr, mGluR1
	Germ cell (testis)	Ma2/Ta
Abbreviations: AChR = acetylcholine receptor; ANNA = antineuronal nuclear antibody; mGluR1 = metabotropic glutamate receptor type 1; nAChR = nicotinic acetylcholine receptor; NMDAR = N-methyl-D-aspartate receptor; PCCA = Purkinje cell cytoplasmic antibody; SCLC = small cell lung carcinoma; VGCC = voltage-gated calcium channels; VGKC = voltage-gated potassium channel; GAD = glutamic acid decarboxylase

Differential Diagnosis

Paraneoplastic cerebellar degradation
- Alcohol abuse
- Vitamin deficiency (thiamine, vitamin E)
- Toxins
- Infectious encephalitis – HIV, HSV
- Creutzfeldt-Jakob disease
- Glutamic acid decarboxylase (GAD)-associated cerebellar ataxia
- Cerebrovascular accident
- Identified malignancy present
  - Cerebellar metastases
  - Chemotherapy toxicity
Opsoclonus-myoclonus
- Infectious encephalitis – HIV, HSV
- Metabolic encephalopathy (hyperosmolar coma)
- Drug effect
- Intracranial hemorrhage
- Systemic disease
  - CNS vasculitis
  - Diabetes mellitus
  - Sarcoidosis
- Identified malignancy present
  - Cerebral metastases
  - Hydrocephalus
Limbic encephalitis and variants
- Wernicke-Korsakoff syndrome (alcohol abuse)
- Systemic disease
  - CNS vasculitis (primary angiitis of CNS)
  - Connective tissue disease
    - Systemic lupus erythematosus
    - Sjögren syndrome
  - Diabetes mellitus
  - Sarcoidosis
- Multiple sclerosis
- Psychiatric disorders
- Metabolic encephalopathy
- Treponema pallidum
- Identified malignancy present
  - Metastases
  - HHV6 limbic encephalitis
  - CNS gliomas
Infectious
- Encephalitis
- HIV
- HSV

Paraneoplastic neurological syndromes (PNS) are diseases occurring due to remote effects of usually malignant tumors. Although many tumors have been associated with PNS, the most common include small cell lung cancer (SCLC), thymoma, neuroblastoma, ovarian, breast, testicular, and Hodgkin lymphoma.

Epidemiology

Incidence – rare
Exceptions
- 3% of patients with SCLC are affected by Lambert-Eaton myasthenic syndrome (LEMS)
- ~10% of patients who have plasma cell disorders with malignant monoclonal gammopathy may be affected by paraneoplastic peripheral neuropathy
- 15% of patients with myasthenia gravis (MG) have thymoma

Pathophysiology

Etiology
- Some forms are autoimmune-mediated
- Immune response against tumors ectopically expressing neuronal antigens is provided by onconeuronal antibodies
- Except in a very few cases (eg, LEMS and recoverin) the direct role of antibodies in the pathogenesis of a PNS has not been proven
Classification of antibodies based on immunohistochemical staining pattern – refer to tables in Diagnosis section

Clinical Presentation

Central nervous system syndromes
- Encephalomyelitis – brainstem, motor dysfunction
- Limbic encephalitis – short-term memory loss, seizures, confusion, dementia
- Subacute cerebellar degeneration – ataxia, slurred speech
- Opsoclonus-myoclonus – involuntary saccadic eye movements may have truncal myoclonus
Peripheral nervous system syndromes
- Subacute sensory neuropathy
- Chronic gastrointestinal pseudo-obstruction
Neuromuscular junction, muscle, joint, bone syndromes
- LEMS – less ocular involvement and more lower limb involvement than classic MG
- Peripheral nerve hyperexcitability (neuromyotonia, Morvan syndrome)
- Dermatomyositis
Visual afferent system (neuro-ophthalmologic PNS) syndromes
- Cancer-associated retinopathy
- Melanoma-associated retinopathy

Tests generally appear in the order most useful for common clinical situations

Test name: Paraneoplastic Antibodies (PCCA/ANNA) by IFA with Reflex to Titer and Immunoblot

ARUP #: 2007961

Methodology: Semi-Quantitative Indirect Fluorescent Antibody/Qualitative Immunoblot

Use:

Aid in the diagnosis of PNS associated with malignancy

Order based on clinical presentation

PCCA/ANNA antibodies are screened by IFA; if IFA screen positive at 1:10, a specific titer (PCCA or ANNA) and immunoblot will be added

Test name: Voltage-Gated Calcium Channel (VGCC) Antibody

ARUP #: 0092628

Methodology: Quantitative Radioimmunoassay

Use:

Aid in the diagnosis of PNS associated with malignancy, or consider in pediatric patients with severe acute encephalitis

Order based on clinical presentation

Follow-up:

Dependent upon clinical history

Test name: Voltage-Gated Potassium Channel (VGKC) Antibody

ARUP #: 2004890

Methodology: Quantitative Radioimmunoassay

Use:

Aid in the diagnosis of PNS associated with malignancy, or consider in pediatric patients with severe acute encephalitis

Order based on clinical presentation

Clinical significance of this test can only be determined in conjunction with patient's clinical history and related laboratory testing

Follow-up:

Dependent on clinical history

Test name: Comprehensive Metabolic Panel

ARUP #: 0020408

Methodology: Quantitative Ion-Selective Electrode/Quantitative Enzymatic/Quantitative Spectrophotometry

Use:

Rule out metabolic disorder as etiology of neurologic deficits

Panel includes albumin, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, bilirubin, calcium, carbon dioxide, creatinine, chloride, glucose, potassium, protein, sodium, and urea nitrogen

Test name: Cell Count, CSF

ARUP #: 0095018

Methodology: Cell Count/Differential

Use:

Rule out infectious process

Test name: Cerebrospinal Fluid (CSF) Culture and Gram Stain

ARUP #: 0060106

Methodology: Stain/Culture/Identification

Use:

Rule out presence of infectious process

Test name: Protein, Total, CSF

ARUP #: 0020514