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Paraneoplastic limbic encephalitis associated with potassium channel antibodies: value of anti-glial nuclear antibodies in identifying the tumour
  1. Luigi Zuliani1,
  2. Albert Saiz1,
  3. Bruno Tavolato2,
  4. Bruno Giometto3,
  5. Angela Vincent4,
  6. Francesc Graus5
  1. 1Service of Neurology, Hospital Clinic, Universitat de Barcelona and Institut d’Investigació Biomèdica August Pi i Sunyer (IDIBAPS), Barcelona, Spain
  2. 2Department of Neuroscience (2 Neurologic Clinic), University of Padua, Padua, Italy
  3. 3Service of Neurology, Treviso, Italy
  4. 4Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, UK
  5. 5Service of Neurology, Hospital Clinic, Universitat de Barcelona and Institut d’Investigació Biomèdica August Pi i Sunyer (IDIBAPS), Barcelona, Spain
  1. Correspondence to:
 Dr L Zuliani
 Department of Neuroscience (2 Neurologic Clinic), University of Padua, Ospedale San’Antonio Via Facciolati 71, Padova 35127, Italy; luigi.zuliani{at}unipd.it

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Limbic encephalitis is characterised by subacute development of short-term memory loss, seizures, confusion and psychiatric features.1 Paraneoplastic limbic encephalitis is generally associated with small cell lung cancer (SCLC), and around 50% of patients harbour Hu, CV2/CRMP5 or amphiphysin antibodies.1 Recently, antibodies against voltage-gated potassium channels (VGKC-abs) were identified as a new marker of a non-paraneoplastic, immunotherapy-responsive form of limbic encephalitis.2,3 However, the presence of VGKC-ab does not exclude a paraneoplastic cause of limbic encephalitis.1

We described previously a new antibody called anti-glial nuclear antibody (AGNA), a marker of SCLC shown to be closely associated with paraneoplastic Lambert–Eaton myasthenic syndrome (LEMS).4 Here we report on two patients with paraneoplastic limbic encephalitis associated with SCLC and VGKC-ab who also presented AGNA.

Methods

The presence of AGNA was assessed by immunohistochemistry on frozen sections of paraformaldehyde-fixed rat cerebellum in nine patients with limbic encephalitis and SCLC with (n = 2) or without (n = 7) VGKC-ab, and in seven patients with non-paraneoplastic limbic encephalitis and VGKC-ab. To confirm AGNA reactivity, an immunohistochemical competition assay was performed as described previously.4 VGKC-abs were detected by radioimmunoprecipitation (cutoff value: 100 pmol/l).2

Case reports

A middle-aged man was admitted to hospital with a 2-week history of behavioural changes and generalised seizures. A neurological examination showed short-term memory loss, confusion and aphasia. Electroencephalography showed slowing in the left temporal lobe. Magnetic resonance …

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