SAT-368 Steroid-Responsive Encephalopathy Associated With Autoimmune Thyroiditis in a Patient With Graves’ Disease

Abstract Disclosure: M. Dominic: None. P. Itersky: None. M.C. Pereira: None. P. Saad: None. D. Englert: None. Background: Steroid-Responsive Encephalopathy associated with Autoimmune Thyroiditis (SREAT), also known as Hashimoto’s encephalopathy, is a rare autoimmune disorder with an estimated prevalence of 2/100,000. It is characterized by acute encephalopathy, presence of anti-thyroid antibodies, and a robust response to corticosteroids. SREAT is most commonly associated with Hashimoto’s disease, although cases associated with Graves’ disease have been previously reported. Prompt recognition is critical for initiating timely treatment with steroids or immunomodulators. Clinical Case: A 45-year-old male with no significant past medical history presented with acute altered mental status, fever, and headache. He was admitted for suspected meningitis after initial evaluation and was started on empiric antimicrobials. He later developed seizures, confirmed on EEG, and was started on levetiracetam. MRI brain revealed edema in the right parietal and posterior temporal lobe cortex. Blood cultures, urinalysis, hepatitis panel, HIV, RPR and West Nile PCR returned negative. CSF studies showed a WBC count of 11 (n 0-5), with 100% lymphocytes, and a negative meningoencephalitis panel, including HSV, HHV-6, and VDRL. Endocrine workup was significant for undetectable TSH (<0.01 μIU/mL, n 0.4-4), elevated T3 (342 ng/dL, n 60-180) & free T4 (3.51 ng/dL, n 0.75-1.5), high thyroid peroxidase (TPO) antibody titers (200 IU/mL, n <6), and positive thyrotropin receptor antibodies consistent with Graves’ disease. The patient was started on methimazole, SSKI and cholestyramine. Despite normalization in free T4 and T3, seizures and altered mentation persisted. Further workup, including a paraneoplastic panel and CSF movement disorder panel, were negative. A diagnosis of antibody-associated autoimmune encephalitis was made at this point, and patient was started on IV methylprednisolone 1 g daily x 5 days, followed by oral prednisone 60 mg daily. Mental status and seizures gradually improved. Repeat brain MRI showed resolution in the cortical edema. The patient was discharged on methimazole and prednisone. Clinical lessons: SREAT is characterized by new encephalopathy of unclear etiology, in the context of elevated anti-thyroid (anti-TPO or anti-thyroglobulin) antibodies. Presentation can vary from mild cognitive dysfunction or psychological abnormalities to status epilepticus and coma. Although it is typically linked to hypothyroidism or euthyroidism, it can rarely occur in hyperthyroid conditions like Graves’ disease. Around 20 cases have been reported globally in association with Graves' disease, as in this case. Corticosteroids are the cornerstone of treatment, with immunosuppressants or plasmapheresis as alternatives. Routine testing for thyroid antibodies in autoimmune encephalitis workups is essential to identify SREAT and prevent delayed treatment. Presentation: Saturday, July 12, 2025