Subclinical hypothyroidism--just a high serum thyrotropin (TSH) concentration or something else?

Association between Subclinical Hypothyroidism and Incident Hypertension in Women: A Systematic Review and Meta-Analysis

Subclinical hypothyroidism (SCH) has been found to be associated with an increased risk of cardiovascular diseases. However, there is no clear consensus on the relationship between SCH and hypertension (HTN). We sought to investigate the association between SCH and incident HTN in women. MEDLINE and EMBASE databases were searched for studies that reported the incidence of HTN in females with SCH versus without SCH. Pooled odds ratio (OR) and 95% confidence interval (CI) of the outcome were obtained using a random-effects model. Studies were also divided into the middle-aged (mean age < 65) and the older (mean age ≥ 65) subgroups, and a subgroup analysis was performed to examine the potential age-effect on the association between SCH and HTN. Nine studies with a total of 21,972 subjects met the inclusion criteria. SCH was found to be positively associated with HTN (OR = 1.32, 95% CI = 1.02–1.71). Such association varied depending on the age of women. In the middle-aged subgroup, SCH was more positively associated with HTN (OR = 1.64, 95% CI = 1.18–2.27), while there was no significant association in the older subgroup (OR = 0.97, 95% CI = 0.80–1.16). Our study showed that the middle-aged females with SCH had an increased risk of HTN, while there was no significant association in the older females with SCH.

Dyslipidemia in subclinical hypothyroidism requires assessment of small dense low density lipoprotein cholesterol (sdLDL-C)

BACKGROUND

Usually both hypothyroidism and hyperthyroidism are related to the cardiovascular and cerebrovascular disease development. The relationship between subclinical hypothyroidism has been widely investigated but the findings remain controversial. The aim of the present study was to evaluate the lipid profile in patients with subclinical hypothyroidism (SHypo) in comparison to controls and to determine the association of SHypo and dyslipidemia in attempt to find importance of small dense low-density lipoprotein cholesterol (sdLDL-C) in atherosclerosis.

MATERIAL AND METHODS

In this study we included 100 women, aged 30 to 70 years that were divided into subgroups according to their age. According to the values of levels of thyroid hormones they were divided into euthyroid (control) group (n = 64) and (newly discovered) subclinical hypothyroidism (SHypo) group (n = 36). A high-sensitivity C-reactive protein (hs-CRP) and lipid profile, including small dense low-density lipoprotein cholesterol (sdLDL-C) were determined. Body weight and height were measured and BMI calculated. History of the current illness, medication, alcohol consumption and cigarettes smoking were noted.

RESULTS

Changed lipid profile as well as elevated triglycerides and sdLDL-C were observed in the group with subclinical hypothyroidism compared to the control group.

CONCLUSIONS

It is important to determine serum lipid levels, especially serum sdLDL-C levels at an early stage of subclinical hypothyroidism, since they represent atherogenic LDL particles and are better indicators for dyslipidaemia in subclinical hypothyroidism and the development of atherosclerosis with potential complications such as cardiovascular and cerebrovascular diseases.

Increased left atrial pressure in non-heart failure patients with subclinical hypothyroidism and atrial fibrillation

BACKGROUND

The impact of subclinical hypothyroidism on the cardiovascular risk is still debated. We aimed to measure the relationship between subclinical hypothyroidism and the left atrial (LA) pressure.

METHODS

The LA pressures and thyroid function were measured in consecutive patients undergoing atrial fibrillation (AF) ablation, who did not have any known heart failure, structural heart disease, or overt thyroid disease.

RESULTS

Subclinical hypothyroidism (4.5≤ thyroid-stimulating hormone <19.9 mIU/L) was present in 61 (13.0%) of the 471 patients included. More subclinical hypothyroidism patients than euthyroid patients (55.7% vs 40.2%; P=0.04).'euthyroid patients had persistent or long-standing persistent AF (55.7% vs 40.2%; P = 0.04). The mean LA pressure (10.9 ± 4.7 vs 9.1 ± 4.3 mmHg; P = 0.002) and LA V-wave pressure (17.4 ± 6.5 vs 14.3 ± 5.9 mmHg; P < 0.001) were, respectively, higher in the patients with subclinical hypothyroidism than in the euthyroid patients. After an adjustment for potential confounders, the LA pressures remained significantly higher in the subclinical hypothyroidism patients. A multiple logistic regression model showed that subclinical hypothyroidism was independently associated with a mean LA pressure of >18 mmHg (odds ratio 3.94, 95% CI 1.28 11.2; P = 0.02).

CONCLUSIONS

Subclinical hypothyroidism may increase the LA pressure in AF patients.

2013 ETA Guideline: Management of Subclinical Hypothyroidism

Subclinical hypothyroidism (SCH) should be considered in two categories according to the elevation in serum thyroid-stimulating hormone (TSH) level: mildly increased TSH levels (4.0-10.0 mU/l) and more severely increased TSH value (>10 mU/l). An initially raised serum TSH, with FT4 within reference range, should be investigated with a repeat measurement of both serum TSH and FT4, along with thyroid peroxidase antibodies, preferably after a 2- to 3-month interval. Even in the absence of symptoms, replacement therapy with L-thyroxine is recommended for younger patients (<65-70 years) with serum TSH >10 mU/l. In younger SCH patients (serum TSH <10 mU/l) with symptoms suggestive of hypothyroidism, a trial of L-thyroxine replacement therapy should be considered. For such patients who have been started on L-thyroxine for symptoms attributed to SCH, response to treatment should be reviewed 3 or 4 months after a serum TSH within reference range is reached. If there is no improvement in symptoms, L-thyroxine therapy should generally be stopped. Age-specific local reference ranges for serum TSH should be considered in order to establish a diagnosis of SCH in older people. The oldest old subjects (>80-85 years) with elevated serum TSH ≤10 mU/l should be carefully followed with a wait-and-see strategy, generally avoiding hormonal treatment. If the decision is to treat SCH, then oral L-thyroxine, administered daily, is the treatment of choice. The serum TSH should be re-checked 2 months after starting L-thyroxine therapy, and dosage adjustments made accordingly. The aim for most adults should be to reach a stable serum TSH in the lower half of the reference range (0.4-2.5 mU/l). Once patients with SCH are commenced on L-thyroxine treatment, then serum TSH should be monitored at least annually thereafter.