P59 – 2522: Steroid responsive photo-paroxysmal response in Hashimoto's encephalopathy

Abstract

Objective To describe an unusual clinical and EEG phenotype of Hashimoto's encephalopathy. Methods A case report and discussion. Results Hashimoto's encephalopathy is rare progressive or relapsing encephalopathy syndrome associated with cognitive decline, seizures and myoclonus. We describe a six year old previously well girl who presented with gradual cognitive decline over a number of months. Work up for this revealed significantly raised thyroid peroxidase antibodies consistent with autoimmune thyroiditis. Therefore a diagnosis of Hashimoto's encephalopathy was made. She had no clinical seizures at presentation or follow up which is unusual for the described phenotype of paediatric Hashimoto's encephalopathy. Her MRI scans revealed global atrophy with multi-focal T2 white matter hyperintensities with no diffusion restriction. An EEG showed spike and polyspike wave complexes with background slowing and photo-paroxysmal responses at multiple frequencies. Other investigations including CSF, VLCFA's, ceruloplasmin, white cell enzymes and urine for organic acids were normal. She was commenced on steroids for Hashimoto's. She showed improvement and of note her previous EEG abnormalities had normalised as well as having no abnormal responses to photic stimulation. Conclusion The absence of prominent seizures is an unusual phenotype of Hashimoto's and presence of photo-paroxysmal responses has been described only in a few other cases in the literature. Our case illustrates that children presenting with Hashimoto's with evidence of CNS involvement should have an EEG including photic stimulation as this represents a potentially treatable entity within Hashimoto's even in those with no overt clinical seizures