Abstract
- Hashimoto encephalopathy (HE) is a rare neurological disorder characterized by encephalopathy associated with autoimmune thyroiditis. While common manifestations include altered mental status, seizures, myoclonus, and neuropsychiatric symptoms, vestibular manifestations as the initial presentation are exceedingly rare. We report a case of a 49-year-old man with a history of hyperthyroidism who initially presented with acute unilateral vestibulopathy. Neurological examination revealed right-beating nystagmus with a negative head impulse test, and caloric testing showed 29.4% left canal paresis. He later developed confusion, ataxia, dysarthria, and psychiatric symptoms. HE was diagnosed based on the clinical features and supportive laboratory findings, including elevated anti-thyroid antibodies and cerebrospinal fluid pleocytosis. The patient showed significant improvement following intravenous methylprednisolone treatment. This case highlights the importance of considering HE in patients with atypical vestibular symptoms, especially those with underlying autoimmune thyroid disease, as timely diagnosis and treatment can lead to a favorable outcome.
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Keywords: Hashimoto’s encephalitis; Vestibular neuronitis; Autoimmune thyroiditis
INTRODUCTION
Hashimoto encephalopathy (HE) is a rare neurological disorder characterized by encephalopathy associated with autoimmune thyroiditis [1,2]. The inner ear was traditionally thought to be protected from systemic immune processes by the blood-labyrinth barrier. However, growing evidence shows that audiovestibular manifestations can occur in various systemic autoimmune diseases, suggesting that this barrier may not provide complete immune privilege [3].
The clinical manifestations of HE are diverse and include altered mental status, seizures, myoclonus, stroke-like episodes, and neuropsychiatric symptoms [4,5]. The diagnosis is based on the presence of elevated anti-thyroid antibodies, encephalopathy features, exclusion of other neurological disorders, and response to steroid therapy [6]. Due to its heterogeneous presentation, HE is often considered a diagnosis of exclusion, and diagnosis can be delayed [1]. Key features distinguishing autoimmune vestibular disorders include poor response to conventional vestibular suppressant medications, atypical patterns on vestibular function tests, and subsequent development of central nervous system symptoms [1,7]. The absence of abnormalities on brain magnetic resonance imaging (MRI) is not uncommon in HE, occurring in approximately 50% of patients [8].
We report a case of HE that initially presented as acute unilateral vestibulopathy, highlighting the importance of considering HE in patients with atypical vestibular symptoms, particularly in those with a history of autoimmune thyroid disease.
CASE REPORT
A 49-year-old man presented to the neurology outpatient clinic with acute spontaneous dizziness and unsteadiness for several days. He had been diagnosed with hyperthyroidism approximately 20 years prior and was taking methimazole. His vital signs were within normal limits. Neurological examination revealed normal ocular alignment with right-beating spontaneous nystagmus without fixation, which was augmented by positional maneuvers and a head-shaking test. The bedside head impulse test was negative. He demonstrated no dysmetria on the finger-to-nose test and had a normal gait, although he showed slight instability during tandem walking. The video head impulse test was normal. The bithermal caloric test revealed a 29.4% canal paresis on the left side (Fig. 1A). These findings were consistent with acute unilateral peripheral vestibulopathy affecting the left side.
The patient was initially managed with conservative treatment. However, after 10 days, his condition deteriorated. He developed slight confusion, ataxia, dysarthria, and psychiatric symptoms including depressive mood and insomnia. The patient did not experience headache at any stage of the illness. Contrast-enhanced brain MRI showed no abnormalities, including absence of meningeal enhancement. Laboratory investigations revealed a decreased thyroid-stimulating hormone (TSH; 0.03 μIU/mL), normal free T4 (1.10 ng/dL), and elevated anti-thyroid antibodies including anti-thyroid peroxidase antibody (1,562.0 IU/mL), TSH receptor antibody (9.06 IU/L), and anti-thyroglobulin antibody (143.00 IU/mL). Paraneoplastic antibodies were negative. Cerebrospinal fluid (CSF) analysis showed pleocytosis with white blood cells of 33/mm3 (lymphocytes 92%), with normal protein and glucose levels.
Based on the clinical presentation, elevated anti-thyroid antibodies, and CSF findings, a diagnosis of HE was made. The patient was treated with intravenous methylprednisolone for 5 days. Following treatment, his symptoms including ataxia, dysarthria, and confusion showed significant improvement, the right-beating nystagmus disappeared, and a follow-up caloric test demonstrated normalization of the left canal paresis (9%, Fig. 1B). Additionally, the anti-thyroid peroxidase antibody level decreased markedly from 1,562.0 IU/mL to 263.9 IU/mL, correlating with the clinical improvement and resolution of vestibular dysfunction.
This case report was approved by the Institutional Review Board of The Catholic University of Korea, Incheon St. Mary's Hospital with a waiver of informed consent due to the retrospective nature of the study and complete anonymization of patient data.
DISCUSSION
This case illustrates an unusual presentation of HE initially manifesting as acute unilateral vestibulopathy. While most previously reported HE cases presented with a constellation of neurological symptoms including confusion, cognitive impairment, speech disorders, and ataxia occurring simultaneously [4], our case is distinctive in documenting the sequential progression from isolated peripheral vestibulopathy to multisystem neurological involvement over a defined timeframe of 10 days, providing valuable insights into the temporal evolution of HE manifestations.
Although vestibular symptoms have been documented in various autoimmune conditions, vestibular presentation as the initial symptom of HE is exceedingly rare [9,10]. The pathophysiology of inner ear involvement in systemic autoimmune diseases, including HE, remains incompletely understood. Multiple mechanisms may contribute to vestibular dysfunction, including immune complex deposition in labyrinthine vessels leading to vasculitis, direct autoantibody attacks against inner ear antigens, and cytotoxic damage to vestibular structures, resulting in sensorineural dysfunction through reduced blood flow and oxidative stress [3,10]. The unilateral presentation may reflect asymmetric immune involvement, as occasional cases of unilateral vestibular dysfunction have been reported in other autoimmune conditions such as Behçet disease, antineutrophil cytoplasmic antibody-associated vasculitides, and immunoglobulin G4-related disease [10].
The diagnostic challenge in autoimmune vestibular disorders lies in their ability to mimic common peripheral vestibulopathies [10]. Several clinical features may suggest an autoimmune encephalopathy such as HE, including subacute onset of neurological symptoms, elevated CSF protein, abnormal electroencephalography findings, and dramatic response to corticosteroid therapy [1,7]. In our patient, the discordance between the negative head impulse test and significant unilateral canal paresis represents a well-documented pattern of dissociation between these two vestibular function tests. While this dissociation pattern is most commonly associated with peripheral lesions such as Ménière disease or chronic vestibular neuritis [11], the subsequent development of encephalopathic symptoms was the critical distinguishing feature that pointed toward a central autoimmune etiology rather than an isolated peripheral vestibulopathy. Normal brain MRI findings are common in HE patients and should not discourage clinicians from considering the diagnosis when clinical and laboratory findings are supportive [1,8].
In HE, high-dose corticosteroids remain the first-line therapy with an excellent response rate of 80% to 90% [6]. Our patient showed remarkable improvement following a 5-day course of intravenous methylprednisolone, with resolution of both his encephalopathic and vestibular symptoms. Objective improvement was documented through follow-up caloric testing, which demonstrated normalization of the left canal paresis from 29.4% to 9%. The dramatic response to corticosteroid therapy not only provides therapeutic benefit but also serves as a diagnostic criterion for HE [6]. However, clinicians should be aware that some patients may require maintenance immunosuppressive therapy to prevent relapses, particularly those with refractory or recurrent symptoms.
Our case emphasizes important clinical considerations for patients with autoimmune backgrounds who develop vestibular symptoms. In patients with pre-existing autoimmune thyroid disease presenting with vestibular dysfunction, clinicians should maintain awareness of potential systemic involvement, particularly when atypical features are present such as poor response to conventional vestibular treatment, progressive symptoms, or development of additional neurological manifestations [3]. The rapid progression from isolated vestibular symptoms to multisystem neurological involvement within 10 days in our patient underscores the importance of serial clinical assessments in this population. Early recognition and appropriate immunosuppressive therapy can result in significant clinical improvement, as demonstrated by our patient’s complete recovery of vestibular function and resolution of all symptoms.
ARTICLE INFORMATION
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Funding/Support
None.
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Conflicts of Interest
No potential conflict of interest relevant to this article was reported.
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Availability of Data and Materials
The datasets are not publicly available but are available from the corresponding author upon reasonable request.
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Authors’ Contributions
Conceptualization, Methodology, Project administration, Visualization: Na S; Data curation, Writing–original draft: Na S, Kim YD; Writing–review & editing: Na S, Kim YD.
All authors read and approved the final manuscript.
Fig. 1.The caloric test. (A) Initial caloric test showing canal paresis of the left side (29.4%). (B) Follow-up test showing normalization of canal paresis after treatment (9% canal paresis, left).
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