Rabbit syndrome in anti-NMDAR antibody encephalitis: a unique association
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LETTER TO THE EDITOR
Rabbit syndrome in anti‑NMDAR antibody encephalitis: a unique association Amlan Kusum Datta1 · Adreesh Mukherjee1 · Alak Pandit1 · Atanu Biswas1 · Biman Kanti Ray1 Received: 12 July 2020 / Accepted: 7 September 2020 © Belgian Neurological Society 2020
Dear Editor, Rabbit syndrome (RS), as described nearly fifty years ago by Villeneuve [1], is an unusual movement disorder, characterized by rapid, fine, involuntary, rhythmic movements, along the vertical axis of mouth. Encephalitis associated with anti N-methyl d-aspartate receptor (NMDAR) antibodies is a severe neurological disease entity, in which hyperkinetic movement disorders are a defining feature [2]. However, until now, RS has not been reported in association with this entity. A 16-year-old girl, of Asian-Indian ethnicity, without a significant past medical record, was admitted to our institute with a one-month history of behavioural perturbations, comprising of worsening mania and temper tantrums, accompanied by multiple episodes of focal seizures with impaired cognition. Examination revealed an afebrile patient, in locked in state, lacking any sign of meningeal irritation. Brain imaging were normal, as were routine blood parameters. Lumbar puncture revealed normal cerebrospinal fluid (CSF) opening pressure, lymphocytic pleocytosis (cells 10, all lymphocytes), mildly elevated protein and normal glucose levels. Viral infectious aetiologies such as herpes simplex virus (HSV) 1 and 2, varicella zoster virus (VZV), Japanese encephalitis virus were excluded by polymerase chain reactions (PCR) assays. Anti N-methyl D-aspartate receptor (NMDAR) antibodies were demonstrated in CSF and a diagnosis of autoimmune encephalitis was made. Presence of ovarian teratoma was excluded by contrast enhanced computerized tomography (CECT) scans of abdomen and pelvis. During course of admission, she developed a fine, rapid, rhythmic oscillatory movement of peri-oral musculature along vertical axis, at a frequency of 4–6 Hz (Hz), * Amlan Kusum Datta [email protected] 1
Institute of Post Graduate Medical Education and Research, Bangur Institute of Neurology, Kolkata, West Bengal, India
sparing the tongue, occurring independent of eye movements (see Video). The movement semiology was consistent with that of RS [1]. She was treated with high dose pulse steroids and intravenous immunoglobulin, following which there was resolution of the peri-oral dyskinesia. However, about one month into admission, she developed features of autonomic instability and succumbed despite intensive care management. RS is limited exclusively to the oral and masticatory muscles, sparing the tongue [1]. This, along with persistence in stage 1 non-rapid eye movement (NREM) sleep, differentiates it from tardive dyskinesias (TD) [3]. Etiology of RS is almost exclusively linked to use of neuroleptic agents, limited to a small fraction of psychiatric patients, who use these drugs [3]. Blockade of pre and post synaptic dopaminergic receptors in the extrapyramidal system, resulting in a
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