Early Detection of Endolymphatic Hydrops in Hypothyroid Patients

Endolymphatic hydrops is acommon inner ear dysfunction. This term often used with meniere's disease and meniere's syndrome. However meniere's is idiopathic by definition where as it can occur secondary to various processes interfering with normal production or absorption of endolymph. Histopathologically, endolymphatic hydrops is seen initially in the cochlear duct and the saccule; with the progression of the disease, subsequent affection of the utricle and semicircular canals (SCC) occur . Vascular alterations, genetic predisposition, hormonal disorders and nutritional and psychological factors might contribute to the genesis of hydrops . Serum antibodies against internal ear antigens and circulating immunocomplexes as well as apositive response to steroid treatment have been reported. Furthermore, MD patients present some features of immune diseases, such as hereditary predisposition, apositive family history for the disease and hypothetic association with certain human leucocyte antigen loci (Cw7, A1, B8) .

The thyroid gland has crucial functions to regulate the endocrine systems through the hypothalamic-pituitarythyroid axis and affect organ-specific such as as Addison's disease and type 1 diabetes mellitus or non-organ-specific such as rheumatoid arthritis and systemic lupus erythematosus .

Ménière's disease is clinically diagnosed by recurrent vertigo attacks combined with cochlear symptoms of primarily low- or mid-frequency sensorineural hearing loss, tinnitus, or ear fullness . The incidence of Ménière's disease varies according to the ethnic population, which is estimated to be about 13-200 person-years . The peak age of onset of Ménière's disease has been reported to be about 40-60 years . The sudden surge of endolymphatic flow, which shifts from the pars inferior (cochlea) to the pars superior (utricle and semicircular canals), stimulates the vestibular hair cells in the cristae of the semicircular canals and may induce vertigo attack in patients with Ménière's disease. However, the pathophysiologic causes for the increase of endolymphatic flow are not understood and are thought to be multifactorial, including abnormal immune response and metabolic endocrine dysfunctions, such as hypothyroidism. Previous studies have suggested the association of hypothyroidism with Ménière's disease . Many studies reported high incidence of thyroid dysfunction in Ménière's disease.

The possible association between (autoimmune) thyroid disease and MD has been postulated for more than 30 years, but it is still controversial. Pulec and House first reported that 3% of patients with MD had a positive history for hyperthyroidism, and Powers et al. found a much higher prevalence of association between MD and hypothyroidism. However, at the beginning of the 1980s, arelationship between altered thyroid function and MD was actually excluded by Kinney and by Meyerhoff et al. , while Evans et al. showed subsequently that 17% of sera from MD patients contained positive anti-thyroidmicrosome antibody titres.

The assessment of patients with Ménière's disease can be challenging. VEMP findings in Meniere's patients varies based on the acuteness and stage of the disease. ~50% of patients with Meniere's disease have asymmetric CVEMP responses, indicating differences in the saccular function (returns to normal in ~50%). Recent reports show different frequency tuning in CVEMP thresholds for 250 Hz - 1 kHz stimuli in patients with endolymphatic hydrops. Some patients show the same pattern in the unaffected ear, perhaps indicating delayed endolymphatic hydrops. 40% of Meniere's patients show improvement in cVEMP amplitude following the administration of furosemide (Seo et al, 2003).