Course and outcome of acute limbic encephalitis with negative voltage-gated potassium channel antibodies

Background: Limbic encephalitis is a potentially treatable immunological condition. The presence of voltage-gated potassium channel antibodies (VGKC-Ab) in the cerebrospinal fluid (CSF) and serum of patients with the condition is a marker of the disease associated with a non-paraneoplastic form and good response to treatment. Recent work has highlighted absent serum VGKC-Ab and distinct immunology in patients with the paraneoplastic form of limbic encephalitis. Methods: The cases of four patients with the typical clinical presentation, neuropsychological features and brain imaging of acute limbic encephalitis, in the absence of any evidence for associated cancer during a follow-up of at least 18 months are described here. Results: All patients had negative testing for VGKC-Ab measured during their acute presentation. All patients made some recovery, although they were left with marked cognitive deficits and persistent seizures. Conclusion: These cases demonstrate that the absence of VGKC-Ab in limbic encephalitis does not necessarily imply a paraneoplastic form. Further work is required to establish the immunological basis for the disorder in these patients, and the optimal treatment regimen.