Pin-point pupils with drowsiness as a presentation of hashimoto's encephalopathy mimicking pontine infarction

Purpose: Hashimoto's encephalopathy (HE) is an autoimmune-mediated encephalopathy with various manifestations. Pupil size change has never been previously reported as a presentation of HE. Case Report: A 65-year-old woman without previous known thyroid disease presented with acute onset of drowsiness and blurred vision. Neurologically, she was drowsy and had bilateral pinpoint-sized pupils without a light reflex, which probably indicated a bilateral pontine lesion. Brain MRI showed two tiny infarctions at the left midbrain and left thalamus, but did not show a pontine lesion, and demonstrated patent vertebral/basilar arteries. Electroencephalography showed intermittent diffuse slowing. She had an elevated protein level (123 mg/dl) in cerebrospinal fluid without pleocytosis. Of note, she had elevated serum levels of anti-TG antibody (282 IU/mL) and anti-TPO antibody (117 IU/mL). Her symptoms improved spontaneously including gradually normalization of her pupil size in 3 days and clear consciousness in 6 days; therefore, corticosteroid was not administered. Conclusion: This case illustrates that physicians should be aware of the treatable condition of HE as a possible diagnosis in patients with bilateral pinpoint pupils and drowsiness but without corresponding MRI lesions.