The value of LGI1, Caspr2 and voltage-gated potassium channel antibodies in encephalitis

The discovery, in 2010, of autoantibodies against the extracellular proteins LGI1 and Caspr2 facilitated a change of view regarding the clinical importance of voltage-gated potassium channel (VGKC) antibodies. Currently, these antibodies are all classified as VGKC-complex antibodies, and are commonly considered to have a similar clinical value. However, studies from the past few years show that the immune responses mediated by these antibodies have differing clinical relevance. Here, we review the clinical importance of these immune responses in three settings: patients with anti-LGI1 antibodies, patients with anti-Caspr2 antibodies, and patients with antibodies against the VGKC complex that lack LGI1 and Caspr2 specificity. Antibodies against LGI1 and Caspr2 are associated with different but well-defined syndromes, whereas the clinical importance of VGKC-complex antibodies without LGI1 and Caspr2 specificity is questionable. We describe each of these syndromes, discuss the function of the target antigens and review the limited paediatric literature on the topic. The findings emphasize the importance of defining these disorders according to the molecular identity of the targets (LGI1 or Caspr2), and caution against the use of VGKC-complex antibodies for the diagnosis and treatment of patients without further definition of the antigen.