SAT-578 Hashimoto's Encephalopathy: An Underreported Syndrome: A Case Report

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Introduction Hashimoto’s encephalopathy (HE) is an immune-mediated encephalopathy associated with Hashimoto’s thyroiditis (HT). Unlike encephalopathy associated with clinical hypothyroidism, HE can arise in euthyroid states as well. We describe a case of subacute encephalopathy in a patient with known Hashimoto’s thyroiditis. Case report A 57 year old male with a history of Hashimoto’s thyroiditis was brought to the hospital with new onset psychosis (delusions, olfactory and auditory hallucinations) and seizure like apneic episodes. He had a tick bite 3 weeks prior but did not demonstrate rash, joint pain, fever, headache or focal neurologic symptoms. He did not have meningismus on exam and demonstrated intact anterograde and retrograde memory. His initial work up including CBC, BMP was unremarkable. Metabolic work up including B1, B12 and ammonia levels were within range and urine toxicology was normal. TSH was elevated up to 7.930 (Ref: 0.27-4.2 Units/ml) while free T4 was 1.39 (Ref: 0.93-1.7 ng/dl). Infectious processes including HIV and syphilis (RPR) were excluded. LP was performed and revealed normal CSF chemistry, microbiology and cell count. CSF Lyme PCR and autoimmune panel was negative. MRI and EEG did not show any structural lesion or epileptic activity, respectively. Given history of Hashimoto’s thyroiditis, we obtained serum anti-thyroid peroxidase level which was elevated at 3,721.5 (Ref: <9 IU/ml). Serum thyroglobulin antibody level was 3.0 (Ref: <2.3 IU/ml). Patient was started on steroids for Hashimoto’s encephalopathy and his symptoms improved within the next 48 hours. Discussion Hashimoto’s encephalopathy was first defined in 1960’s but has been subject to controversy. Its exact pathophysiology is unknown, however majority of evidence points towards an autoimmune process. The disease can manifest years before the clinical onset of Hashimoto’s thyroiditis and may represent a separate or parallel disease process. HE has a variable clinical presentation however two syndromes have been commonly described. 1) Stroke-like subtype with acute or sub-acute focal deficits 2) Diffuse progressive subtype with encephalopathy, rapidly progressive dementia, psychosis and seizures. Elevated TPO antibodies are the mainstay of diagnosis and demonstrate high specificity in the appropriate setting. Other diagnostic modalities (CSF analysis, brain MRI/CT and EEG) may demonstrate non-specific abnormalities. The syndrome carries a benign prognosis and is largely reversible with steroids thus highlighting the importance of timely diagnosis. Conclusion Hashimoto’s encephalopathy is an underdiagnosed etiology of encephalopathy. HE should be strongly considered in a patient with unexplained neurologic symptoms and psychosis once relevant etiologies have been ruled out. Anti-thyroid antibodies should be included as first tier investigation in encephalopathy work up.