High Grade Glioma Mimicking Voltage Gated Potassium Channel Complex Associated Antibody Limbic Encephalitis

Though raised titres of voltage gated potassium channel (VGKC) complex antibodies have been occasionally associated with extracranial tumours, mainly presenting as Morvan's Syndrome or neuromyotonia, they have not yet been reported to be associated with an intracranial malignancy. This is especially important as misdiagnosis of these conditions and delay of the appropriate treatment can have important prognostic implications. We describe a patient with a high grade glioma presenting with clinical, radiological, and serological features consistent with the diagnosis of VGKC antibody associated limbic encephalitis (LE). This is the first association between a primary brain tumour and high titre of VGKC complex antibodies. Clinicoradiological progression despite effective immunosuppressive treatment should prompt clinicians to look for alternative diagnoses. Further studies to elucidate a possible association between VGKC complex and other surface antigen antibodies with primary brain tumours should be carried out. 1. Introduction VGKC complex antibody associated LE is considered a nonparaneoplastic, immunoresponsive condition typically presenting subacutely with memory loss, confusion, seizures, and behavioural changes (though visual hallucinations and psychosis have also been reported) [1]. Approximately 60% of patients have high signal changes unilaterally or bilaterally in the medial temporal lobes on FLAIR and T2 weighted MR imaging [1]. Serum hyponatremia, another diagnostically useful feature, is present in around 60% of patients [2]. The diagnosis is usually made with a combination of clinicoradiological findings and the presence of high titre VGKC complex antibodies (normal reference range is <100 picomolar (pM)). Though it is uncertain at what level a titre of antibody becomes significant, previous studies have suggested titres greater than 400？pM as “high” and levels above this seem to be more associated with CNS disease [1, 2]. Though the phenotype of VGKC complex antibody associated LE is continually expanding, other important conditions can often mimic the initial presentation and alternative diagnoses should be considered in atypical cases. Intracranial malignancy is an important differential diagnosis and can present with similar symptoms; however, there have been no reports of elevated levels of VGKC complex antibodies being found in association with an intracranial malignancy. We report a case of a patient presenting initially with characteristic features of VGKC complex associated LE with elevated levels of VGKC antibodies in his serum