BS14. Visual and brainstem auditory evoked potentials in Hashimoto’s thyroiditis

Abstract

Introduction A normal thyroid gland activity is essential for the optimal development, maturation and function of the nervous system. Neurological syndromes can develop in certain thyroid diseases that may have normal levels of thyroid hormones. One such example is Hashimoto’s thyroiditis (HT), which is currently considered to be the most common autoimmune disease in humans. The exact cause of those symptoms has not yet fully been explained. Their pathomechanism is still being studied. Precise and non-invasive methods of assessment of the nervous system function is evoked potentials study (EP). It is a sensitive technique that enables the evaluation of the brain bioelectrical activity also in patients with HT. EPs are particularly useful in patients with mild or without clinical neurological symptoms. The aim of the study was to evaluate parameters of visual and brainstem auditory evoked potentials (VEP, BAEP) in euthyreotic HT patients without clinical neurological deficit, and without ophthalmological and otolaryngological abnormalities. Methods 100 HT patients (92 women, 8 men) from 20 to 68 years old (mean 46.9 years). They did not suffer from concurrent diseases that could have affected the brain electrical activity. The visual and auditory receptors were not damaged in any of the patients and the patients did not suffer from any central nervous system damage. The matched control group comprised 50 healthy subjects. HT patients underwent a subjective and objective neurological examination, thyroid hormone levels and thyroid autoantibody titers, brain imaging (CT or MRI), VEP and BAEP. Results Abnormal VEP and BAEP were recorded in 34% of the patients. The mean P100, relative P100, N145 VEP latencies were significantly longer and P100 amplitude significantly higher in HT patients than in the control group. HT patients also had a longer mean wave V latency and mean wave III-V and I-V interpeak latencies and significantly lower mean wave I and V amplitudes than the controls. There were no statistically significant correlations between the mean VEP parameters and the levels of TSH, free thyroid hormones, antithyroid antibody titers and the applied dose of L-thyroxine. There was a relationship between the level of TSH and the wave BAEP III-V interpeak latency. The number of abnormal VEP and BAEP depended on the dose of L-thyroxine and was the highest in patients without treatment and decreased with the increase in the dose of levothyroxine. Conclusion 1. There were changes in the brain bioelectrical activity in the form of abnormal VEP and BAEP in one third of the patients with Hashimoto’s disease who did not have central nervous system deficits. 2. The increased amplitude of the VEP in the course of HT may indicate increased cerebral cortex activity. 3. Disorders of the brain bioelectrical activity in the course of HT may be associated with an ongoing autoimmune process. 4. The analysis of the VEP and BAEP may be useful in assessing the brain bioelectrical activity in the course of HT.