What EEG findings are characteristic of Hashimoto myoclonic encephalopathy?

Updated: Oct 09, 2019
  • Author: Eli S Neiman, DO, FACN; Chief Editor: Selim R Benbadis, MD  more...
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Ghika-Schmid et al reported 2 patients with subacute diffuse encephalopathy characterized by confusion, myoclonic encephalopathy, and mild akineto-rigid extrapyramidal signs in one case and by apathy, memory deficit, and partial complex seizures in the other. Hashimoto thyroiditis with high titers of antithyroglobulin antibodies was diagnosed in both patients, who were not responsive to anticonvulsant medication but exhibited rapid neurologic improvement following steroid treatment. On neuropsychological examination, predominant frontotemporal dysfunction was noted. [89]

EEG activity was remarkable for its rhythmic delta activity, which was unresponsive to, or even paradoxically increased by, anticonvulsant treatment. Atrophy with temporal predominance was observed on MRI. These observations support the idea that this potentially treatable dementia and movement disorder should be classified as a separate clinical entity.

Kothbauer-Margreiter et al reported 6 patients with Hashimoto thyroiditis and associated encephalopathy and compared with 14 well-documented cases identified in the literature. [90] Encephalopathy typically affects patients when they are euthyroid and in an appropriate clinical situation; antithyroid autoantibodies are the main indicators of the encephalopathy. Since clinical features of Hashimoto encephalopathy are nonspecific, other etiologies, such as infectious, metabolic, toxic, vascular, neoplastic, and paraneoplastic causes, must be considered.

Two types of initial clinical presentation can be differentiated:

  • A vasculitic type with strokelike episodes and mild cognitive impairment

  • A diffuse progressive type with dementia, seizures, psychotic episodes, or altered consciousness

These types may overlap, particularly over the long term in untreated patients. A strong female predominance existed in the study by Kothbauer-Margreiter et al ; 18 of the 20 patients were women. The EEG was abnormal in 90% of cases; it showed nonspecific changes. The condition is steroid-responsive.

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