Characterization of neurological morbidity associated with thyroid antibodies: Hashimoto's encephalopathy and beyond

Background: Hashimoto's Encephalopathy (HE) manifests with various neurologic symptoms associated with elevated thyroglobulin (TG) and/or thyroperoxidase (TPO) antibodies. Some patients with thyroid antibodies exhibit neurological presentations not consistent with HE. This study aims to characterize the spectrum of neurological morbidity in patients with thyroid antibodies. Methods: We reviewed all patients tested for TG or TPO antibodies from 2010 to 2019. Patients tested for thyroid antibodies as part of a neurological workup for new symptoms were classified into the following categories: patients meeting full criteria for HE, patients with other neuroimmunological disorders, patients with unexplained neurological symptoms not fully meeting HE criteria, and patients with incidental non neuroimmunological disorders. Results: There were 2717 patients with positive thyroid antibodies in the dataset including 227 patients (78% female, age 54 +/- 19 years) who met inclusion criteria. Twelve patients (5%) met HE criteria, 30 (13%) had other neuroimmunological disorders, 32 (14%) had unexplained neurological symptoms, and 153 (67.4%) had incidental disorders. In addition to cognitive dysfunction, seizures, movement disorders, motor weakness, and psychosis, HE patients were also more likely to have cerebellar dysfunction, language impairment, and sensory deficits. They were more likely to carry a Hashimoto's thyroiditis diagnosis and had higher titers of thyroid antibodies. They all had a robust response to steroids. Conclusion: The neurological spectrum of HE may be wider than previously reported, including frequent cerebellar, sensory, and language dysfunction. A subgroup of thyroid antibody positive patients with unexplained neurological symptoms may represent further expansion of thyroid antibody-related neurological disorders.