Recurrent Seizure-Like Episodes Revealing Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis: A Case Report

Suwanee, GA

Introduction

Steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT), also known as Hashimoto encephalopathy, is a rare autoimmune condition characterized by encephalopathy, seizures, cognitive impairment, and neuropsychiatric manifestations in the presence of elevated antithyroid antibodies. The estimated prevalence is approximately 2.1 per 100,000 individuals, and the condition remains underrecognized due to its highly variable clinical presentation. Neuroimaging is often normal, and electroencephalography typically demonstrates nonspecific abnormalities such as diffuse slowing. Additionally, thyroid antibody testing is not routinely included in the evaluation of seizure-like activity or unexplained encephalopathy, which may delay diagnosis. As a result, SREAT is often diagnosed only after extensive workup excludes more common neurologic, infectious, metabolic, or structural etiologies.

Methods

We present the clinical course of a 60-year-old female with a history of hypothyroidism, type-2 diabetes, hypertension, and presumed seizure disorder who presented with recurrent seizure-like episodes and altered mental status. Clinical findings, laboratory studies, neuroimaging, electroencephalographic data were reviewed during hospitalization. Diagnostic evaluation included continuous electroencephalography (cEEG), MRI brain, CT of chest, abdomen, and pelvis, infectious workup, metabolic testing, and thyroid antibody (anti-TPO) evaluation. The patient’s clinical progression and response to antiepileptic medications and corticosteroids therapy were monitored throughout hospitalization.

Results

The patient presented with recurrent seizure-like episodes occurring up to ten times a day, including generalized motor activity and prolonged staring spells. Six months prior, she had been evaluated for new-onset seizures following a gastrointestinal illness. At that time, diagnostic studies including MRI brain, cerebrospinal fluid analysis, autoimmune panels, and routine EEG were unrevealing, and she was started on levetiracetam. During the current admission, continuous EEG demonstrated generalized rhythmic delta activity with disorganized background suggestive of diffuse cerebral dysfunction but without clear epileptiform discharges. Repeat neuroimaging, infectious workup, and CT imaging of the chest, abdomen, and pelvis to evaluate for malignancy were all unremarkable. Laboratory testing revealed markedly elevated anti–thyroid peroxidase antibodies with stable thyroid hormone levels. Given the unexplained encephalopathy, elevated thyroid antibodies, and response to steroid treatment, SREAT was suspected. The patient was treated with antiepileptic therapy including levetiracetam and valproic acid, followed by initiation of high-dose corticosteroids, resulting in significant improvement in mental status and resolution of seizure-like episodes.

Discussion

This case demonstrates the diagnostic complexity associated with SREAT and highlights the importance of maintaining a broad differential diagnosis in patients presenting with refractory seizure-like episodes and unexplained encephalopathy. When conventional diagnostic evaluation is unrevealing, SREAT should be considered, particularly given the potential for significant neurological improvement with appropriate corticosteroid therapy.