23 Jan Hypothyroidism Affects Olfactory Evoked Potentials

Hypothyroidism Affects Olfactory Evoked Potentials

Analysis of the correlation between TSH values and latencies of smell cortex evoked responses to olfactory and trigeminal nerves stimulation indicated that the greater the TSH value, the longer the latency of the recorded potential. Mean values, ranges, and standard deviations of recorded latency times of olfactory potentials PN1 and PN5 for all the groups of the subjects in stimulation with concentrated vapors of mint and anise oils. Currently there is insufficient knowledge about olfaction and taste functions in subclinical hypothyroidism, which represents a specific subgroup of hypothyroidism. Aim of the present study was to investigate the degree of smell and taste dysfunction in this group compared to healthy controls. Hypothyroidism has been found to have long-term effects on each of the senses, but with proper treatment, many of them can be significantly minimized. This paper analyzes the research on the impact of hypothyroidism on the senses of smell, taste, hearing, vision, and thermoregulation.

Studies were excluded if they were outside this paper’s scope or older than 2012. Studies were included if they specifically focused on hypothyroidism and one of the five listed senses. Patients with hypothyroidism had a significantly increased risk of sensorineural buying synthroid hearing loss, decreased perception of the blue-yellow color axis, decreased sense of olfaction and number of olfactory bulbs, and decreased thermogenesis. Hypothyroidism was also found to show increased length of COVID-19-induced anosmia and decreased bitter taste perception. It can be concluded that hypothyroidism has many effects on the senses, particularly an increased risk of sensorineural hearing loss.

What is the thyroid connection to the sense of smell?

It was possible to differentiate responses to stimuli irritating nerve V endings (potential PN5 within latency range 200–410 ms) as well as nerve I endings (potential PN1 within latency range 460–700 ms). The Kruskal-Wallis, Mann-Whitney’s significant differences tests, descriptive statistical tests, and Spearman’s rank correlation tests were used. In the subjective olfactory tests performed using Ellsberg’s olfactory test method modified by Pruszewicz in the hypothyroid patients, the smell perception thresholds (mint and anise) were normal in 85% cases. Definition of subclinical hypothyroidism requires normal levels of T3/T4 and increased TSH. Treatment of subclinical hypothyroidism doesn’t change levels of free T3 and T4 levels, reduces TSH levels to normal interval. Günbey et al. 19 investigated olfactory function in primary hypothyroid patients and found significantly lower scores in the hypothyroid group and a positive correlation between all threshold, discrimination and identification scores and free T3 levels.

Defects of taste and smell in patients with hypothyroidism

• Hypothyroidism was also found to show increased length of COVID-19-induced anosmia and decreased bitter taste perception.
• Her background includes caring for patients in women’s health, critical care, pediatrics, allergy, and immunology.
• Treatment of subclinical hypothyroidism doesn’t change levels of free T3 and T4 levels, reduces TSH levels to normal interval.
• Twenty eight subclinical hypothyroid patients, and 31, age, gender, education level matched participants enrolled in the study.
• Application of the olfactory stimulus is synchronized with the inspiration phase of the subject in our study.

According to a 2018 review in the World Journal of Otorhinolaryngology Head and Neck Surgery, studies and reviews show that more than 350 drugs can cause changes in taste, and more than 70 drugs can cause changes in smell. Our study included 31 controls and 28 untreated subclinical hypothyroid patients. Mean age was 29±8.5 years in the control group and 29.9±9.0 years in the study group. Groups did not differ significantly in terms of age, sex and education level (Table 1).

• The method is however subjective, depending on individual perception of the patient.
• The messages sent to your brain about both taste and smell travel along similar signaling pathways.
• Subclinical hypothyroidism has been accused for coronary heart disease, atherosclerosis, lipid metabolism disorders, neuropsychiatric disorders, infertility or pregnancy related problems with various strength of evidence 2,5.
• In this paper we show for the first time that the greater the TSH values, the longer the latency of smell cortex potentials recorded from both the trigeminal nerve N5 and the olfactory nerve N1.
• Your provider may be able to change the drug for you or suggest methods to improve your sense of taste or smell.

Dealing with Hypothyroidism? Video chat with a thyroid doctor

Implementing this method in diseases of the upper respiratory tract as a complementary method, for instance, in injuries of the craniofacial skeleton and surgical operations of the nasopharyngeal tumors, has already become quite common 5–7, 26, 27. Statistical analyses were performed using SPSS software version 15 (SPSS Inc. Chicago, IL, USA). The variables were investigated using descriptive (histograms, probability plots) and analytical methods (Kolmogorov—Smirnov test) to determine whether or not they were normally distributed. Descriptive analyses were presented as means ± standard deviations for normally distributed variables. For non-normally distributed/ordinal variables descriptive statistics are presented with number of cases with percentage, medians and interquartile range (IQR). Differences between numeric variables of two groups were tested with independent samples Student’s t-test for continuous variables displaying normal distribution and Mann—Whitney U test for continuous variables not displaying normal distribution.

Is There Any Effect on Smell and Taste Functions with Levothyroxine Treatment in Subclinical Hypothyroidism?

Prevalence of subclinical hypothyroidism is relatively high among elderly and women. Our taste and smell sensations have their own receptor organs, but they are closely connected. Likely, your ability to taste your food is also reduced until your nasal congestion resolves. When food doesn’t taste right, it can alter your appetite and change your eating habits.

Most importantly, these deficits can be remedied on average within 3 months with adequate treatment. Graphs in Figures 1 and 2 present a comparison of mean values, ranges, and standard deviations of PN1 and PN5 potentials in the subclinical and overt clinical hypothyroid groups as well as in controls. The apparatus for recordings of ERP (evoked reaction potentials) as well as the authors’ self-designed device that enables appropriate dispensing of olfactory stimuli were used 15. The modified self-designed device for objective measurement of cortex reaction potentials evoked by olfactory stimuli, which proves to be a unique investigation, is at present routinely used in our center in diagnostics and clinical evaluation of the organ of smell. Disturbances in perception thresholds of the olfactory test within the subjective scale were evaluated using Ellsberg’s olfactory method modified by Pruszewicz 13, 17. The method is however subjective, depending on individual perception of the patient.

Accordingly, we also looked for a similar relation between olfaction and thyroid function tests in subclinical hypothyroid patients but did not find a positive correlations. Regarding changed fT3 levels in the normal interval of our results, expected correlation wouldn’t be occured. Apart from an effect on subjective perception of fragrances, a symptom of olfactory disorders proves to be a change in parameters of objective ERP recording of smell cortex potentials such as latency time or response amplitude.

How Long After Starting Thyroid Medication to Lose Weight?

Correlation analysis were made with Pearson’s and Spearman’s correlation analyses, respectively. Some people also attribute changes in taste to the medication used to treat thyroid conditions, such as thyroid hormone replacement medications. For example, some reports indicate that it is not uncommon to have a metallic taste in your mouth if you take levothyroxine. However, one study found that altered taste improved significantly in the study group after being on levothyroxine for three months. The fact is we don’t know exactly why an altered sense of taste can be a symptom of a thyroid issue. But, one more recent study of hypothyroidism shows evidence that low thyroid hormone can lead to burning mouth syndrome and an altered taste sensation.

All the subjects underwent subjective threshold tests of smell perception determined by Ellsberg’s olfactory test modified by Pruszewicz and olfactory objective tests recording latency times of responses from cranial nerves I and V using two smells of mint and anise. In the study by McConnell 12 et al. smell and taste function was tested in 18 overt hypothyroid patients before and after treatment. Smell and taste tests were made with interrogation with the patients and similar testing methods which we have used. This study indicates that taste and smell deficits are common in hypothyroid patients and these deficits could be reversed with treatment. Fikentscher, who had used the olfactory method according to Ellsberg, obtained clear cortex responses with latency time 500–1000 ms 24.