Encephalopathy associated to autoimmune thyroid disease: a more appropriate term for an underestimated condition?

Abstract

Hashimoto’s encephalopathy is a severe and rather infrequent clinical condition initially described in patients suffering from chronic lymphocytic thyroiditis. Its origin is still controversial but it can be agreed to have an autoimmune etiology. In fact, its most characteristic finding is the high titre of antithyroid antibodies, especially antimicrosomal. We describe three cases of Hashimoto’s encephalopathy and establish a relationship between the clinical status, the antithyroid antibody levels and its response to corticosteroid treatment. There was an excellent response to corticosteroid treatment in all three cases. Interestingly, one case was associated with Graves’ disease. Given this, and after the review of the literature, we believe that the term ‘encephalopathy associated to autoimmune thyroid disease’ could be more appropriate to define this entity. Finally, we suggest that autoimmune thyroid encephalopathy must be suspected in the face of unaccounted acute or subacute encephalopathy with high levels of antithyroid antibodies.

Introduction

Hashimoto’s encephalopathy (HE) is a life-threatening clinical condition initially described in patients suffering from chronic lymphocytic thyroiditis. Although rather infrequent, it must be taken into consideration when encephalopathy is associated to high levels of antithyroid antibodies, even in the absence of known thyroid disease.

Originally HE was postulated to be a distinct disease entity by Brain et al. [1]. The main clinical features of HE are altered consciousness, stroke-like events, seizures, tremor, and myoclonus. On neurological examination, pyramidal tract signs without clear focal deficit are frequently found. Investigation of these patients characteristically shows diffuse electroencephalogram (EEG) abnormalities and high cerebrospinal fluid (CSF) protein levels without pleocytosis, although the most relevant issue is the high titre of antithyroid antibodies found in most cases [2]. Since there are no clinical, laboratory or neuroimaging findings that are specific for this entity, the exhaustive exclusion of infectious, metabolic, toxic, vascular, neoplastic and paraneoplastic causes of encephalopathy is mandatory.

To date there are 28 well-documented cases of HE in the literature [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. We describe three new cases, one of them unusual in that it was associated with Graves’ disease, and make some remarks on its pathogenesis. Finally, we provide some arguments to consider ‘encephalopathy associated to autoimmune thyroid disease’ a more suitable term than Hashimoto’s encephalopathy to refer to this entity.