Increased prevalence of sublinical brain perfusion abnormalities in patients with autoimmune thyroiditis: evidence of Hashimoto's encephalitis?

OBJECTIVES

Hashimoto's encephalitis is a term which describes encephalopathy associated with autoimmune thyroiditis, but it is not based on evidence, whether Hashimoto's encephalitis is a distinct clinical entity by itself. In previously reported cases of Hashimoto's encephalitis, abnormal brain perfusion studies have been reported. The aim of this study was to evaluate the prevalence of brain perfusion abnormalities in euthyroid patients with autoimmune thyroiditis.

METHODS

99mTc Ethyl cystein dimer (ECD) single photon emission computed tomography (SPECT) studies were performed in a study group of 41 euthyroid patients with autoimmune thyroiditis and a matched control group of 35 healthy individuals. All study participants had a normal neurological investigation and a detailed neurological history taking. Individuals with known or suspected morphological brain abnormalities were excluded from the study. Zung's Self-Rating Anxiety Scale (SAS) and Zung's Self-Rating Depression Scale (SDS) were used to detect depression and mood disorders. Automatic quantification of perfusion was performed with both a voxel-based analysis as well as a volume-of-interest (VOI) based analysis of 46 predefined cortical and subcortical regions. The findings from both groups were compared to a reference template.

RESULTS

In the voxel-based analysis, there was a significant difference between patients and controls in the mean volume of perfusion defects deviating 2SD below the normal values (21.8 ml vs. 10.4 ml; P = 0.02). Hyperperfused areas, however, did not differ significantly between study patients and controls. A significant correlation of the perfusion defects with time since diagnosis of autoimmune thyroiditis was seen (r = 0.42). In the VOI-based analysis, abnormal regions were more frequent in the study group when compared to controls (P < 0.01) However, no topographic pattern was apparent. Regarding neurological findings, no significant difference was found between study patients and controls. However, both the SAS and SDS scores differed significantly between the two groups, but there was neither a correlation between the two scores and perfusion abnormalities nor an association with depression in our study group.

CONCLUSIONS

These findings of impaired brain perfusion in patients with autoimmune thyroiditis further strengthen the hypothesis of a possible cerebral involvement in autoimmune thyroiditis in individual cases. The presence of cerebral hypoperfusion suggests a cerebral vasculitis as the most likely pathogenetic model.