Thyroid Hormone Replacement Therapy Improves Olfaction and Taste Sensitivity in Primary Hypothyroid Patients: A Prospective Randomised Clinical Trial

Smell and taste are known to be influenced by thyroid function changes. However, many hypothyroid patients and physicians are unaware of their dysosmia and dysgeusia. The present study was performed to shed more light on the relation between hypothyroidism and olfactory loss. 32 primary hypothyroid patients and 31 controls enrolled in the prospective randomized interventional study. Newly diagnosed Primary hypothyroid patients were treated with L-thyroxine for 3-6 months. The control group was selected on the basis of the biochemical evidence of a normal thyroid function. Psychophysiological olfactory testing was performed using odor dispensers similar to felt-tip pens (Sniffin' Sticks, Burghart, Wedel, Germany). Taste function tests were made using Taste Strips (Burghart, Wedel, Germany) which are basically tastant adsorbed filter paper strip. Smell identification, threshold, discrimination, TDI scores, bitter and sweet taste scores were significantly lower in untreated hypothyroid patients compared to controls (12.31 +/- 1.09 vs. 14.03 +/- 1.05, p<0.001; 7.09 +/- 1.15 vs. 8.89 +/- 1.12, p<0.001; 11.47 +/- 0.95 vs. 13.06 +/- 0.85, p<0.001; 30.90 +/- 2.70 vs. 35.89 +/- 2.07, p<0.001; 4.88 +/- 1.6 vs. 6.64 +/- 0.96, p<0.001; and 5.5 +/- 2.22 vs. 6.58 +/- 1.28, p=0.021) respectively. Comparison of scores at the third month of treatment and before treatment of hypothyroid patients revealed significant improvement in smell and taste functions in terms of identification, threshold, discrimination, TDI scores, bitter, sweet and salty tastes (12.31 +/- 1.09 vs. 13.84 +/- 1.22, p<0.001; 7.09 +/- 1.15 vs. 8.02 +/- 1.16, p<0.001; 11.47 +/- 0.95 vs. 12.41 +/- 1.21, p<0.001; 30.90 +/- 2.70 vs. 34.27 +/- 3.25, p<0.001; 4.88 +/- 1.6 vs. 6.06 +/- 1.4, p<0.001; 5.5 +/- 2.22 vs. 6.38 +/- 1.28, p<0.001; and 6.12 +/- 2.32 vs. 6.62 +/- 1.48, p=0.044) respectively. On correlation analysis, there was a negative correlation between TPO-Ab levels and discrimination, identification and TDI scores (r=-0.409, p=0.02; r=-0.424, p=0.016; r=-0.532, p=0.002), and also between Tg-Ab levels and identification, TDI, and bitter scores (r=-0.423, p=0.016; r=-0.468, p=0.007; r=-0.409, p=0.02) respectively. Primary hypothyroidism was found to have a negative effect on smell and taste. RAI treatment was found to be most destructive on smell and taste compared to surgical and autoimmune hypothyroidism. Treatment of hypothyroidism was positively correlated with an improvement of both senses. Thus, the future workup of patients with smell/taste loss should include investigations for thyroid functions.