Autoimmune encephalopathy presenting as a ‘posterior circulation stroke’

Abstract

Antibodies to voltage gated potassium channels (VGKC) can result in a reversible form of encephalopathy [1]. Since first described, the clinical phenotype of patients with antibodies to VGKC continues to expand [2]. To our knowledge this is the first reported case of VGKC encephalopathy mimicking a stroke resulting in misdiagnosis. A 73 year old woman presented with aphasia and right upper limb weakness, 5 days post-carotid endarterectomy for an asymptomatic 90% left carotid stenosis. She had experienced atrial fibrillation (warfarin had not yet been reintroduced), hypertension, diabetes and was an ex-smoker. A CT brain done within 12 h of presentation did not show any evidence of infarction (Fig. 1). Diffusion weighted (DWI) magnetic resonance imaging (MRI) of the brain, done 2 days after presentation, demonstrated an increased signal in the left temporal lobe in the region of the hippocampus, amygdala and extending to the pulvinar region of the thalamus (Fig. 2). Restricted diffusion was seen on apparent diffusion coefficient (ADC) in the same territory, consistent with a thromboembolic infarct. A diagnosis of thromboembolic event to the left posterior cerebral artery (PCA) was made and the patient was transferred to the acute stroke unit. Warfarin was restarted and, following improvement over a month, she was transferred to a rehabilitation facility. However, after 2 weeks the patient developed visual hallucinations and was re-admitted. On arrival she had three convulsive seizures and was treated with intravenous phenytoin. A repeat MRI brain was performed (Fig. 3), 2 months from initial presentation, again showing high signal on DWI and corresponding restricted diffusion on ADC map in the same distribution as the initial imaging. Following review of the MRI imaging, the lesions were deemed to be inconsistent with a PCA infarct. Cerebrospinal fluid protein was normal and an electroencephalogram showed delta slowing in the left temporal region and intermittent sharp waves. A whole body fluorodeoxyglucose positron emission tomography (FDG–PET) scan did not show any evidence of malignancy. Voltage gated potassium channels (VGKC) levels were 1,726 pico Moles (normal \100 pM), paraneoplastic antibodies were negative. A diagnosis of autoimmune limbic encephalitis (LE) was made, as described with VGKC antibodies [1–4]. The patient was treated with methylprednisolone with an improvement in both receptive and expressive components of language. Repeat antibodies were unrecordable following initial treatment and she was discharged on oral prednisolone. She was re-admitted on two further occasions while on oral steroids. On each recurrent admission, she received methylprednisolone with a corresponding decrease of VGKC antibodies. Mycophenolate mofetil was added when a level of 2,026 pM was recorded. A wide clinical phenotype is seen in VGKC autoimmunity [2] including: Isaacs syndrome [5], Morvan H. Kearney B. Murray K. O’Rourke P. Kelly T. Lynch (&) The Dublin Neurological Institute at the Mater Misericordiae University Hospital, 57 Eccles Street, Dublin 7, Ireland e-mail: Tlynch@mater.ie URL: http://www.neurologicalinstitute.ie