Brain hyper-excitability in DPPX ataxia
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LETTER TO THE EDITORS
Brain hyper‑excitability in DPPX ataxia M. Pattrick1 · P. G. Sarrigiannis1 · S. Kruger3 · B. Davies4 · N. Hoggard2 · S. R. Irani5 · Z. Unwin1 · P. Zis1 · D. J. Blackburn1 · Marios Hadjivassiliou1 Received: 26 May 2020 / Revised: 15 June 2020 / Accepted: 20 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Dear Sirs, DPPX antibody-related ataxia (DPPX-ARA) was first described in 2013 [1]. The original four patients reported presented with agitation, hallucinations, confusion, myoclonus, tremor and seizures. Three patients had a prodromal diarrheal illness. DPPX is an auxiliary, regulatory protein of the Kv4.2 potassium channel, involved in increasing the activity and surface expression of the Kv4.2 channel [2]. This channel serves in attenuating the back propagation of action potentials under resting conditions. Its internalisation, due to DPPX-antibodies and their effect on neurones, is thought to be the pathophysiological basis of autoantibodyinduced CNS-hyperexcitability responsible for this disease [3, 4]. We present three cases with DPPX-ARA (positive serological test on live based assay) that underwent detailed neurophysiological assessments alongside cerebellar MR spectroscopy pre and post immunotherapy [5]. Two patients also had gastroscopy and duodenal biopsies as part of investigation for severe weight loss. Two patients presented with ataxia and tremor. The third with apathy, depression and visual hallucinations. All patients had lost significant weight (15, 45 and 60 kg) prior to the neurological presentation. Clinical examination
* Marios Hadjivassiliou [email protected] 1
Academic Department of Neurosciences, Sheffield Teaching Hospitals NHS Trust, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK
2
Department of Neuroradiology, Sheffield Teaching Hospitals NHS Trust and University of Sheffield, Sheffield, UK
3
Department of Psychiatry, Doncaster, UK
4
Department of Neurorehabilitation, Doncaster and South, Humber NHS Trust, Doncaster, UK
5
Oxford Autoimmune Neurology Group, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
demonstrated irregular tremor affecting the arms. They all startled to noise. Two had horizontal nystagmus and no significant limb ataxia. All had gait ataxia. Suspicion for DPPXARA was raised because of 60Kg weight loss. The positive result prompted us to recall and test the female patient that had been seen several years before with suspected immune ataxia. She had lost 45Kg. Because of the weight loss both these patients underwent gastroscopy and duodenal biopsies despite no serological evidence of celiac disease. The biopsies were normal. Gluten-free diet was trialled by one of the patients but it did not help the ataxia. Electrophysiological assessment using EEG/EMG polygraphy was done to assess the myoclonus. Data were analysed with the technique of jerk-locked averaging (JLA) [6]. All patients underwent somatosensory evoked potentials (SEP) to assess t
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