EEG findings in steroid-responsive encephalopathy associated with autoimmune thyroiditis

Objective: To analyze the electroencephalogram (EEG) findings of patients with steroid-responsive encephalopathy associated with autoimmune (Hashimoto) thyroiditis. Methods: We reviewed 51 EEGs and the clinical records of 17 patients (5 men and 12 women, 27-84 years old). Results: All patients had mild to severe generalized slowing on the EEG which corresponded to the clinical severity of the underlying encephalopathy. Other findings included triphasic waves, epileptiform abnormalities, photomyogenic response, and photoparoxysmal response. Follow-up EEGs of 13 patients showed slowing in 7 and a return to normal in 6. Myoclonic jerks were recorded during the EEG study of 8 patients but did not have an EEG correlate. The EEG and clinical condition improved after treatment with corticosteroids. When encephalopathy recurred, the EEG showed corresponding abnormalities. Conclusions: EEG findings in steroid-responsive encephalopathy associated with autoimmune thyroiditis consist mainly of slow wave abnormalities that reflect the degree of severity of the underlying encephalopathy. The EEG findings often paralleled the course of the disease, showing improvement with improvement in the clinical condition and worsening with recurrence of symptoms. Significance: The EEG is helpful in evaluating and following patients with steroid-responsive encephalopathy associated with autoimmune thyroiditis in reflecting the degree of central nervous system (CNS) involvement, in determining whether their condition is better or worse, and in ruling out other causes of encephalopathy.