Influence of subclinical hypothyroidism on parameters of tear production in patients with hypertension

Abstract

A high incidence, continuous growth rates as well as collected data on modifying influence of subclinical hypothyroidism (SH) on cardiovascular disease, necessitate the improvement of clinical diagnostic methods of hypothyroidism at the early stages. Thyroid hypofunction has been proved to be influential in the tear fluid secretion and dry eye syndrome development. However, there is insufficient evidence of tear production parameters use for hypothyroidism diagnosis at the preclinical stages in patients with cardiovascular disease. The aim of the work – to improve the diagnostics of SH in hypertensive patients by examining tear production parameters using the Schirmer test. Materials and methods. 102 patients with essential hypertension stage II were enrolled in the study after signing an informed consent. Depending on the thyroid stimulating hormone (TSH) level patients were divided into 2 groups - with normal (0.4–4.0 mU\ml) and moderately increased level of TSH (4.0–15.6 mU\ml with normal levels of thyroid hormones). The group of hypertensive patients without SH included 71 patients (83.1 % of women (59) and 16.9 % of men (12)), the group of hypertensive patients with concomitant SH consisted of 31 patients (90.32 % of women (28) and 9.68 % of male, (3)). Patient groups were matched for age (55.11 ± 8.67 years versus 58.09 ± 10.04 years; P = 0.131), gender (P = 0.363), height (P = 0.821), weight (P = 0.832), body surface area (P = 0.780), body mass index (P = 0.885). Apart from laboratory thyroid screening (TSH, Free T4), all patients underwent the Schirmer test according to the standard procedure. There were conducted ROC-analysis, univariate logistic regression analysis, Bland-Altman analysis; the Mann-Whitney U-test and χ2 were used. Results. The average levels of TSH in hypertensive patient groups with euthyroidism and SH were 1.98 ± 0.82 mU\ml and 7.12 ± 2.96 mU\ml (P = 0.0001), the Schirmer test mean values – 20.02 ± 8.8 mm and 8.45 ±7.66 mm (P = 0.0001), respectively. According to the ROC-analysis the critical value of Schirmer test was indicator of13 mm (sensitivity 93.7%, specificity 69.6 %, AUC 0.853; 95 % CI 0.703–0.945; P = 0.0001). Univariate logistic regression analysis has shown that in patients with hypertensive disease the Schirmer test values ≤13 mm increased odds ratio for SH by 21.44 times (95 % CI 3.76–312.72, P = 0.0017). Results of Bland-Altman analysis have demonstrated high consistency of the data obtained by different methods of SH diagnosis. Conclusions. In hypertensive patients with concomitant SH a decrease in tear production according to the Schirmer test has been detected. The Schirmer test value of less than13 mm per 5 minutes should be considered as a criterion for SH diagnosis in hypertensive patients. Application of Bland-Altman method in comparing two methods of diagnosis allows using the Schirmer test for screening (prior to TSH levels determination) in patients with hypothyroidism as an additional factor of cardiovascular risk in patients with arterial hypertension.

Keywords

• hypertension
• subclinical hypothyroidism
• Schirmer test