Abstract
Benign paroxysmal positional vertigo (BPPV) is a common form of dizziness that is provoked by changes in head position (1).
Some authors (2) have proposed that BPPV may be triggered by the movement of immune-complexes in the inner ear with consequent mechanical stimulation of labyrinthine receptors. Recently, we found a 34% prevalence of Hashimoto's thyroiditis (HT), a chronic form of thyroiditis, in BPPV patients (3). In our previous letter (3), we compared a group of patients with BPPV with a group of age- and sex-matched healthy subjects without a history of vertigo or thyroid disease. We noted that the mean serum thyrotropin (TSH) was higher in the BPPV group than in the healthy controls and that the titers of anti-thyroid peroxidase antibodies (TPO-Ab) and anti-thyroglobulin antibodies (Tg-Ab) were also higher in the BPPV group than in the controls. Twenty-one percent of the BPPV group had hypothyroidism, whereas only 2% of the control group had it. Moreover, anti-thyroid antibodies were positive in 46 of the BPPV group, whereas they were positive in only 2 subjects of the control group. The association of BPPV with elevated anti-thyroid antibodies (odds ratio [OR] 25.6) was stronger than the association of BPPV with hypothyroidism (OR 12.9). Our previous study (4), therefore, demonstrated an association between thyroid disease and BPPV but did not establish clearly whether this association was between BPPV and decreased thyroid function or between BPPV and thyroid autoimmunity. Therefore, we performed a further study to determine whether BPPV was associated with euthyroid HT. We prospectively recruited 200 patients with euthyroid HT (Group HT-Eu), who were consecutively referred to the Division of Endocrinology, “A. Gemelli” Hospital—Catholic University of Rome and to the Endocrine Outpatient Clinics of “Ramazzini” Hospital—Azienda USL of Modena, Italy, from April 1, 2008 to April 30, 2009. During this period, 818 patients were referred due to HT; however, 618 individuals—326 due to overt hypothyroidism and 292 due to subclinical hypothyroidism—were excluded from the study. Two hundred age- and sex-matched healthy blood donors (Group C) were also included in the study and served as controls. In both study groups, the prevalence of BPPV was determined. The results were statistically analyzed by means of unpaired Student's t-test (two-tailed) for continuous variables (serum hormones and antibodies) and by means of Chi-square test, df 1, for nominal variables (BPPV and ultrasound HT pattern). Statistical significance was taken as p < 0.05.
The diagnosis of BPPV was based on the following criteria: sudden onset of short and temporary (few second-lasting) episodes of rotational vertigo provoked by positioning tests (Dix-Hallpike manoeuvre for posterior semicircular canal or lateral head positionings for lateral semicircular canals) (4,5).
The following inclusion and exclusion criteria were used to assign patients to Group HT-Eu. Inclusion criteria were (a) male and female patients older than18 years; (b) normal serum TSH and free thyroxine concentrations; (c) high Tg-Ab and/or TPO-Ab levels. Exclusion criteria were (a) pregnancy; (b) personal history of arterial hypertension, diabetes mellitus, migraines, head trauma, alcohol abuse, psychiatric, inner ear, and cerebrovascular diseases; (c) medications. The inclusion and exclusion criteria for the Group C were as follows: adult male and female healthy patients without personal history of either dizziness or thyroid disease.
Patients belonging to Group HT-Eu and Group C were subjected to the following procedures: measurement of serum TSH (normal values: 0.3–4 mIU/L), free thyroxine (0.8–1.8 pg/mL), Tg-Ab (<100 IU/L), and TPO-Ab (<40 IU/L) antibody concentrations; thyroid ultrasound; and otoneurology visit. Individuals with signs/symptoms of BPPV underwent complete neurological examination; eye movement testing; evaluation of spontaneous nystagmus and dynamic vestibule-ocular reflex function; Dix-Hallpike manoeuvre (4); and lateral head positionings (5).
The study protocol was approved by the local ethics committee (register N. 64/2008). All individuals gave informed consent to diagnostic procedures.
In Group HT-Eu, 160 out of 200 (80%) patients were female and 40 (20%) were male, aged 49 ± 4 years (median 48 years). In Group C, 160 out of 200 (80%) patients were female, aged 48.2 ± 5.2 years (median 47 years; p = non significant [NS] vs. Group HT-Eu). The results of this study are summarized in Table 1. BPPV was diagnosed in 36 (18%) patients of Group HT-Eu and in 4 (2%) subjects of Group Cs; 2 out of 4 control individuals with BPPV presented with overt hypothyroidism due to HT.
Groups were matched for age and sex.
BPPV, benign paroxysmal positional vertigo; FT4, free thyroxine; Group HT-Eu, euthyroid patients affected by HT; Group C, healthy control subjects; HT, Hashimoto's thyroiditis; HT pattern, diffusely hypoechoic thyroid gland; Tg-Ab, anti-thyroglobulin antibodies; TPO-Ab, anti-thyroperoxidase antibodies; TSH, thyrotropin; US, ultrasound.
To our knowledge, this work represents the first case–control study evaluating the occurrence of BPPV in patients with euthyroid HT. Our data show a higher BPPV prevalence in patients with HT than in subjects of the control group. They demonstrate, on the one hand, that HT and BPPV are strongly linked and, on the other hand, that such a link is related to the presence of thyroid autoantibodies, independently of thyroid function. We propose two possible etiopathological explanations for this evidence: (1) either precipitation of thyroid autoantibody immune-complexes in the inner ear with mechanical stimulation of labyrinthine receptors or (2) a coexisting autoimmune microangioitis of the labyrinth associated with HT in the context of an autoimmune multiorgan syndrome. Whichever that may be, based on the results of the present work and previous studies (2,3), we suggest that thyroid autoimmunity be always checked in the work-up of patients with BPPV.