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Abstract
Objective: To assess the clinical relevance of a positive voltage-gated potassium channel (VGKC) test in patients lacking antibodies to LGI1 and Caspr2.
Methods: VGKC-positive patients were tested for LGI1 and Caspr2 antibodies. Patients lacking both antibodies were matched (1:2) to VGKC-negative patients. Clinical and paraclinical criteria were used to blindly determine evidence for autoimmune inflammation in both groups. Patients with an inconclusive VGKC titer were analyzed in the same way.
Results: A total of 1,455 patients were tested by VGKC radioimmunoassay. Fifty-six patients tested positive, 50 of whom were available to be included. Twenty-five patients had antibodies to LGI1 (n = 19) or Caspr2 (n = 6) and 25 patients lacked both antibodies. Evidence for autoimmune inflammation was present in 7 (28%) of the VGKC-positive patients lacking LGI1 and Caspr2, compared to 9 (18%) of the VGKC-negative controls (p = 0.38). Evidence for autoimmune inflammation was mainly found in patients with limbic encephalitis/encephalomyelitis (57%), but not in other clinical phenotypes (5%, p < 0.01). VGKC titers were significantly higher in patients with antibodies to LGI1 or Caspr2 (p < 0.001). However, antibodies to Caspr2 could also be detected in patients with inconclusive low VGKC titer, while many VGKC-positive patients had no evidence for autoimmune inflammation.
Conclusions: VGKC positivity in the absence of antibodies to LGI1 and Caspr2 is not a clear marker for autoimmune inflammation and seems not to contribute in clinical practice. No cutoff value for the VGKC titer was appropriate to discriminate between patients with and without autoimmune inflammation.
GLOSSARY
- AMPAR=
- AMPA receptor;
- Caspr2=
- contactin-associated protein-like 2;
- CBA=
- cell-based immunofluorescence assay;
- CJD=
- Creutzfeldt-Jakob disease;
- EM=
- encephalomyelitis;
- GABABR=
- GABAB receptor;
- LE=
- limbic encephalitis;
- LGI1=
- leucine-rich glioma-inactivated protein 1;
- mRS=
- modified Rankin Scale;
- NMDAR=
- NMDA receptor;
- RIA=
- radioimmunoassay;
- VGKC=
- voltage-gated potassium channel
Footnotes
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Editorial, page 1657
Supplemental data at Neurology.org
- Received September 18, 2015.
- Accepted in final form December 22, 2015.
- © 2016 American Academy of Neurology
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Disputes & Debates: Rapid online correspondence
- Clinical syndrome matters in all patients, with or without a positive VGKC-test (without LGI1/Caspr2-antibodies) (authors' reply)
- Voltage-gated potassium channel antibodies: Clinical syndrome matters
- Thorough study, in line with raw data within the literature (authors' reply)
- Small sample, overstated conclusions
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