Hashimoto's encephalopathy mimicking a brain tumor and its pathological findings: A case report.

Hashimoto's encephalopathy is characterized by the presence of anti-thyroid antibodies with no alternative cause. Patients with Hashimoto's encephalopathy present with various clinical symptoms and magnetic resonance imaging (MRI) findings. To our knowledge, this is the first documented report of Hashimoto's encephalopathy with MRI findings mimicking a brain tumor. The patient was a 41-year-old woman with a history of Hashimoto's disease. She experienced gradually worsening Parkinsonism and an MRI revealed a brain tumor-like lesion at the left caudate nucleus. She underwent a brain biopsy that revealed diffuse gliosis and perivascular lymphocyte infiltration with CD3+ T-cell predominance. No pathological signs of a brain tumor were found. Hashimoto's encephalopathy was suspected based on the patient's history and the presence of anti-thyroid antibodies. Her symptoms and the MRI findings improved with glucocorticoid treatment. Although there exist only a few studies on the pathology of Hashimoto's encephalopathy, our findings were consistent with those of previous reports. Our findings suggest cerebral vasculitis as an underlying etiology of Hashimoto's encephalopathy. We also emphasize the importance of considering Hashimoto's encephalopathy as a differential diagnosis of brain tumors.