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Delayed LGI1 seropositivity in voltage-gated potassium channel (VGKC)-complex antibody limbic encephalitis
Michael Sweeney1, Jonathan Galli1, Scott McNally2
1Department of Neurology, University of Utah, Salt Lake City, Utah, USA.
Insights
Early testing for voltage-gated potassium channel (VGKC)-complex antibodies is crucial for diagnosing autoimmune encephalitis. Even with initial negative LGI1/CASPR2 results, persistent VGKC positivity warrants further investigation and prompt immunotherapy.
Area of Science:
- Neurology
- Immunology
- Clinical Medicine
Background:
- Autoimmune encephalitis can present with diverse neurological symptoms, including faciobrachial dystonic seizures (FBDS).
- Serological testing for voltage-gated potassium channel (VGKC)-complex antibodies is essential for diagnosing specific autoimmune encephalitides.
- Leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) are common targets within the VGKC-complex.
Observation:
- A 68-year-old male presented with involuntary movements suggestive of FBDS.
- Initial serology showed VGKC-complex antibody positivity but LGI1 and CASPR2 antibody negativity.
- The patient received early immunotherapy (methylprednisolone and plasmapheresis) with subsequent clinical improvement.
Findings:
- Repeat testing revealed persistent VGKC-complex antibody positivity and the emergence of LGI1 autoantibodies after 4 months.
- Both VGKC-complex and LGI1 antibodies remained positive at 12-month follow-up.
- Clinical symptoms may precede detectable antibody levels in some cases.
Implications:
- Exclusion of VGKC-complex antibody testing can lead to diagnostic delays in autoimmune encephalitis.
- High clinical suspicion for autoimmune encephalitis with VGKC-complex antibody positivity necessitates early immunotherapy and potentially repeat testing, irrespective of initial LGI1/CASPR2 status.
- This case underscores the dynamic nature of autoantibody profiles and the importance of comprehensive serological evaluation.
Abstract:
We utilise a clinical case to highlight why exclusion of voltage-gated potassium channel (VGKC)-complex autoantibody testing in serological evaluation of patients may delay or miss the diagnosis. A 68-year-old man presented with increasing involuntary movements consistent with faciobrachial dystonic seizures (FBDS). Initial evaluation demonstrated VGKC antibody seropositivity with leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) seronegativity. Aggressive immunotherapy with methylprednisolone and plasmapheresis was started early in the course of his presentation. Following treatment with immunotherapy, the patient demonstrated clinical improvement. Repeat serum evaluation 4 months posthospitalisation remained seropositive for VGKC-complex antibodies, with development of LGI1 autoantibody seropositivity. VGKC-complex and LGI1 antibodies remained positive 12 months posthospitalisation. Our findings suggest that clinical symptoms can predate the detection of the antibody. We conclude that when suspicion for autoimmune encephalitis is high in the setting of VGKC autoantibody positivity, regardless of LGI1 or CASPR2 seropositivity, early immunotherapy and repeat testing should be considered.
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