Quantitative Radioimmunoassay/Semi-Quantitative Cell-Based Indirect Fluorescent Antibody
- Screening test for VGKC antibody receptor complex-associated autoantibodies
- Reflexes to CASPR2 and LGI1 antibodies
Quantitative Radioimmunoassay/Semi-Quantitative Cell-Based Indirect Fluorescent Antibody
Quantitative Radioimmunoassay
Screening test for VGKC antibody receptor complex-associated autoantibodies
Quantitative Radioimmunoassay
Screening test for VGKC antibody receptor complex-associated autoantibodies
Semi-Quantitative Cell-Based Indirect Fluorescent Antibody
Aids in diagnosis of LGI1 disorders
Semi-Quantitative Cell-Based Indirect Fluorescent Antibody
Aids in diagnosis of LGI1 disorders
Semi-Quantitative Cell-Based Indirect Fluorescent Antibody
Aids in diagnosis of CASPR2 disorders
Semi-Quantitative Cell-Based Indirect Fluorescent Antibody
Aids in diagnosis of CASPR2 disorders
Semi-Quantitative Cell-Based Indirect Fluorescent Antibody
Aids in diagnosis of LGI1 and CASPR2 disorders
Semiquantitative Cell-Based Indirect Fluorescent Antibody/Quantitative Radioimmunoassay/Semiquantitative Enzyme-Linked Immunosorbent Assay
- Aid in the differential evaluation of encephalitis of unknown origin with subacute onset of seizures, confusion, memory loss, and/or behavioral change
- For adults and patients with suspicion of cancer, additional evaluation of paraneoplastic autoantibodies is recommended; refer to Paraneoplastic Reflexive Panel (3002929)
See the Anti-NMDA Receptor (NR1) IgG Antibodies Test Fact Sheet for more information on the evaluation of NMDA antibodies in autoimmune encephalitis.
Quantitative Radioimmunoassay/Qualitative Radiobinding Assay/Semi-Quantitative Flow Cytometry/Semi-Quantitative Indirect Fluorescent Antibody
- Acceptable reflexive panel for the differential diagnosis of acquired neuromuscular junction disorders
- Panel includes acetylcholine receptor binding, blocking, and modulating antibodies; ganglionic acetylcholine receptor antibodies; P/Q-type and N-type voltage-gated calcium channels; voltage-gated potassium channels; titin antibody; striated muscle antibodies; leucine-rich glioma-inactivated protein 1 antibody; and contactin-associated protein-2 antibody IgG with reflex to titers.
See Related Tests.
Voltage-gated potassium channel antibody disorders include limbic encephalitis, faciobrachial dystonic seizures, and peripheral nerve hyperexcitability disorders that may occur following immunotherapy and/or plasmapheresis.
Disease Overview
Incidence
Unknown
Symptoms
- Limbic encephalitis (mainly LGI1 antibodies):
- Amnesia
- Seizures
- Disorientation
- Psychiatric disturbance
- Peripheral nerve hyperexcitability
- Neuromyotonia
- CSF usually normal
- Morvan syndrome (mainly CASPR2 antibodies):
- Limbic encephalitis
- Neuromyotonia
- Confusion
- Amnesia
- Insomnia
- Pain
- Autonomic dysfunction: hyperhidrosis, constipation, urinary incontinence
Diagnostic Issues
Antibody testing may aid in diagnosis.
- Testing should be performed only when neuromuscular and/or neurological symptoms are present.
- Anti-VGKC disorders are rare and present with symptoms similar to those of other encephalitic disorders.
- Antibody testing should not be used for screening.
- Antibodies may be associated with paraneoplastic (autoimmune) or nonparaneoplastic neurological disorders.
- Not all neurological disorders or antibodies are associated with tumors.
- In most antibody-mediated, non-neoplastic-associated diseases, individuals improve substantially with immunotherapy.
- It is important to diagnose these illnesses due to therapeutic responsiveness.
Physiology
- VGKC autoantibodies:
- Directed against a protein that is complexed with potassium channels in both the peripheral nervous system and CNS
- CASPR2:
- Present in ~50% of individuals with neuromyotonia
- CASPR2 antibodies are common in individuals with thymic malignancies.
- LGI1:
- Not directed against the potassium channels
- Associated with limbic encephalitis, faciobrachial dystonic seizures, hyponatremia, and myoclonic movements
- Disorders are rarely associated with tumors
- CASPR2:
- Directed against a protein that is complexed with potassium channels in both the peripheral nervous system and CNS
- VGKC radioimmunoassay (RIA) tests can be used as a general screen for VGKC-complex antibodies directed against:
- LGI1
- CASPR2
- Other unidentified targets
Test Interpretation
Results
VGKC Antibody, Serum
- Positive: >88 pmol/L
- Suggests VGKC antibody-related disease
- Indeterminant: 32-87 pmol/L
- Retest in 2-4 weeks
- Negative: 0-31 pmol/L
- Likelihood of VGKC antibody-related disease is reduced but not necessarily eliminated
VGKC Antibody, CSF
- Positive: >1.1 pmol/L
- Suggests VGKC antibody-related disease
- Negative: 0.0-1.1 pmol/L
- Likelihood of VGKC antibody-related disease is reduced but not necessarily eliminated
LGI1 Antibody, Serum
- Positive: ≥1:10
- Suggests LGI1 antibody-related disease
- Negative: <1:10
- Does not rule out disorders associated with VGKC complex antibodies
CASPR2 Antibody, Serum
- Positive: ≥1:10
- Suggests CASPR2 antibody-related disease
- Negative: <1:10
- Does not rule out disorders associated with VGKC complex antibodies
Limitations
VGKC Antibody
- Presence of VGKC antibodies should be used in conjunction with clinical manifestations for:
- Neuromyotonia spectrum of disorders
- VGKC antibody-associated limbic encephalitis
- Should not be used as the sole criterion for diagnosis
- VGKC receptor-complex proteins may be coprecipitated by anti-VGKC antibodies, including:
- LGI1
- CASPR2
- Other unidentified targets