Overt and Subclinical Hypothyroidism

Abstract

Hypothyroidism denotes deficient production of thyroid hormone by the thyroid gland and can be primary (abnormality in thyroid gland itself) or secondary/central (as a result of hypothalamic or pituitary disease). The term 'subclinical hypothyroidism' is used to define that grade of primary hypothyroidism in which there is an elevated thyroid-stimulating hormone (TSH) concentration in the presence of normal serum free thyroxine (T4) and triiodothyronine (T3) concentrations. Subclinical hypothyroidism may progress to overt hypothyroidism in approximately 2-5% cases annually. All patients with overt hypothyroidism and subclinical hypothyroidism with TSH >10 mIU/L should be treated. There is consensus on the need to treat subclinical hypothyroidism of any magnitude in pregnant women and women who are contemplating pregnancy, to decrease the risk of pregnancy complications and impaired cognitive development of the offspring. However, controversy remains regarding treatment of non-pregnant adult patients with subclinical hypothyroidism and serum TSH values ≤10 mIU/L. In this subgroup, treatment should be considered in symptomatic patients, patients with infertility, and patients with goitre or positive anti-thyroid peroxidase (TPO) antibodies. Limited evidence suggests that treatment of subclinical hypothyroidism in patients with serum TSH of up to 10 mIU/L should probably be avoided in those aged >85 years. Other pituitary hormones should be evaluated in patients with central hypothyroidism, especially assessment of the hypothalamic-pituitary-adrenal axis, since hypocortisolism, if present, needs to be rectified prior to initiating thyroid hormone replacement. Levothyroxine (LT4) monotherapy remains the current standard for management of primary, as well as central, hypothyroidism. Treatment can be started with the full calculated dose for most young patients. However, treatment should be initiated at a low dose in elderly patients, patients with coronary artery disease and patients with long-standing severe hypothyroidism. In primary hypothyroidism, treatment is monitored with serum TSH, with a target of 0.5-2.0 mIU/L. In patients with central hypothyroidism, treatment is tailored according to free or total T4 levels, which should be maintained in the upper half of the normal range for age. In patients with persistently elevated TSH despite an apparently adequate replacement dose of LT4, poor compliance, malabsorption and the presence of drug interactions should be checked. Over-replacement is common in clinical practice and is associated with increased risk of atrial fibrillation and osteoporosis, and hence should be avoided.

Prevalence and characteristics of anemia associated with thyroid disorders in non-pregnant Saudi women during the childbearing age: A cross-sectional study

“…[2][3][4][5] Hypothyroidism, either in overt or occult form, is the most common type with a prevalence of up to 20% in the elderly population. [6][7][8][9]13] Despite the fact that thyroid disorders are frequently encountered in Saudi Arabia, these conditions are understudied and there is a lack of information on their prevalence, types, and etiological factors contributing to their development. [26,27] The findings of the present study agree with the previous findings and show that the overall prevalence of thyroid disorders was 19.6%, suggesting that thyroid dysfunction is a common endocrine disorder in non-pregnant Saudi females, at least in the Western province of the kingdom.…”

“…[6][7][8] The prevalence of thyroid disorders differs from one society to another and hypothyroidism is the most prevalent type with a reported frequency of 2-5% worldwide. [7,9] Also, the prevalence of subclinical hypothyroidism is approximately 4-8.5% and it can increase to up to 20% in women aged 60 years or older. [6,7,10] Alternatively, hyperthyroidism is less prevalent with a frequency ranging between 0.5 and 2% in women.…”

A comparative study of sensory-motor coordination, executive function, and testosterone levels in hypothyroid and euthyroid males

“…[12] The newly diagnosed hypothyroid group consisted of 4 overt hypothyroid cases (with serum TSH levels above 4.5 μIU/ml and low T4 levels), and 11 subclinical hypothyroid cases (with serum TSH levels between 4.5 and 10 μIU/ml and T4 levels within normal limits). [13] The serum testosterone levels of all 30 participants were within the normal range for the age group. A comparative analysis of both groups revealed that there was a statistically significant difference in the visual reaction time, auditory reaction time, and working memory scores, with the euthyroid group outperforming the hypothyroid group in all of these parameters.…”

The Economic Impact of Changing Levothyroxine Formulations in Difficult-to-Treat Hypothyroid Patients: An Evidence-Based Model

“…Numerous published studies have demonstrated the difficulty of maintaining patients in the guideline-recommended therapeutic range for TSH using levothyroxine, with as many as 32-48% of patients being categorized as having either a "subadequate" or "excessive" response to therapy [3,[43][44][45][46]. Factors affecting levothyroxine efficacy include patient persistence and compliance, medication tolerability, Since levothyroxine is an NTI drug, small differences in dose or blood concentration may lead to therapeutic failures or adverse drug reactions [4][5][6][7][8][9]47]. It is not surprising that patients, pharmacists, and physicians have been concerned regarding the use of generic NTI drugs with varying levels of potency [48], particularly in diseases such as hypothyroidism.…”

“…Levothyroxine is classified as a narrow therapeutic index (NTI) medication, which indicates that small differences in absorption or bioavailability may lead to therapeutic failure or adverse drug reactions [4][5][6][7][8][9]. Currently, levothyroxine medications are available in various formulations, including compressed tablets (generic and branded) and soft gel caps.…”