Vertigo and dizziness associated with thyroid autoimmunity
Vertigo and dizziness can occur when the vestibular system (parts of the inner ear and brain that process sensory information to control balance and eye movements) is disturbed, and a study recently published in Clinical Endocrinology shows a strong association with vestibular disorders like vertigo and thyroid autoimmunity. This may come as no surprise to readers since vestibular disorders often have an autoimmune component and thyroid autoimmunity is so common. The authors note:
"In the last years, coexisting AITD has been described in a percentage of patients with vestibular disorders, as Ménière's disease (MD) or benign paroxysmal positional vertigo (BPPV). In the former disease, an autoimmune origin has been postulated, and we recently showed a relationship between MD and thyroid autoimmunity regardless of thyroid function. Similarly, a higher prevalence of BPPV in euthyroid AITD patients than in healthy controls has been reported. These findings suggest an actual relationship between vestibular disorders and thyroid autoimmunity independently from thyroid function...To shed more light on the relationship between vestibular lesions and Hashimoto's thyroiditis (HT) regardless of thyroid function, we examined vestibular function in euthyroid HT patients as compared to either age-matched patients with benign multinodular goitre (MNG) or healthy subjects without any thyroid disorder."
They examined data for 47 patients with HT, 21 with multinodular goitre (MNG) and 30 healthy volunteers, all of whom had normal thyroid function tests and no complaints of vertigo or other vestibular dysfunction. Besides obtaining a detailed history of vertigo, they all were subjected to a thorough vestibular evaluation that included the Caloric Test, Vestibular evoked myogenic potentials (VEMPs), and the Head Shaking Test (HST). Anti-TG and anti-TPO antibodies along with TSH, FT3 and FT4 were also measured. A clear association was found with thyroid autoimmunity as distinct from multinodular goitre:
"52·2% of HT patients showed an alteration of VEMPs and 44·7% of caloric test. None of the MNG patients showed any vestibular alteration, while one healthy control showed an altered caloric test. A correlation was found between vestibular alterations of HT patients and the degree of serum TPOAb level, not affected by age and serum TSH value. By logistic regression analysis, the absence of thyroid autoimmunity significantly reduced the risk of vestibular alterations: HR 0.19 for caloric test; HR 0·07 for VEMPs; and HR 0·22 for HST."
Clinical Note: This association will be completely missed by clinicians who examine patients with vertigo for thyroid dysfunction only by looking at TSH and T4.
Hashimoto's thyroiditis is not limited to the thyroid
Practitioners experienced in the case management of autoimmune disorders are aware that loss of immune tolerance almost always involves more than one tissue target for inflammation. This is echoed in their comments about Hashimoto's thyroiditis and fibromyalgia (FM):
"Overall, these findings further support the relatively novel concept that HT is not a well-defined organ-specific autoimmune disease, as traditionally considered, but may lead per se to systemic clinical manifestations. Accordingly, recent reports documented a significant comorbidity between fibromyalgia (FM) and HT regardless of thyroid function, and the presence of circulating antithyroid autoantibodies worsened FM symptoms, suggesting a pathogenic role of thyroid autoimmunity. Moreover, an electron microscopic study of skeletal muscle biopsies from euthyroid subjects suffering from HT showed capillary alteration and mononuclear cell infiltrate of skeletal muscles, suggesting a relationship between thyroid autoimmunity and FM symptoms. Finally, a recent study, enrolling 426 consecutive euthyroid HT females, suggested that euthyroid HT patients might be affected by a generalized autoimmune process as part of the continuum of connective tissue diseases, with significant rheumatic manifestations."
Risk of progression to Meniere's disease
The authors detail
"The present study documents a strong association between euthyroid Hashimoto's thyroiditis and vestibular subclinical alterations, suggesting that circulating antithyroid autoantibodies may represent a risk factor for developing vestibular dysfunction...The presence of circulating autoantibodies in MD patients suggests a predisposition for autoimmune diseases or, at least, a general reactivity against 'self' antigens."
Moreover...
"The reported high prevalence of coexisting autoimmune systemic diseases in patients affected by MD further supports the hypothesis of a pathogenic role of the immune system in MD. Although several studies documented a high prevalence of HT in patients affected by MD and BPPV...Papi et al. reported a higher prevalence of BPPV in patients with euthyroid HT than in healthy controls. A hypothetic role of immune complexes precipitation in the inner ear with concomitant autoimmune microangioitis was postulated as pathogenic mechanism shared with HT."
Regarding the endolymphatic hydrops typical of Meniere's disease...
"Giving that no HT patient was affected by canalolithiasis, we can hypothesize that the saccular dysfunction detected by VEMPs could rely on early endolymphatic hydrops that, in some cases, may evolve in full-blown Ménière's disease. Moreover, 53·6% of the patients with an alteration of VEMPs showed also labyrinthine deficit, an expression of root canal damage probably due to hydrops extended to the entire endolymphatic system. Such data can, at least partially, support the hypothesis of immune-mediated damage on sites of production or reabsorption of endolymph in the inner ear, as suggested by our previous reports."
Practitioners must be alert to the link between vertigo and autoimmunity
"In conclusion, the present study demonstrates the existence of a clear relationship between thyroid autoimmunity and subclinical vestibular damage, regardless of thyroid function. Specifically, a significant association between vestibular alterations and the degree of TPOAb titre was observed. This finding suggests that circulating antithyroid autoantibodies may represent a risk factor for developing vestibular dysfunction. An accurate vestibular evaluation of HT patients with or without symptoms is therefore warranted."