From the Guidelines
Subclinical hypothyroidism (SCH) is typically diagnosed with elevated Thyroid-Stimulating Hormone (TSH) levels and normal thyroxine (T4) and triiodothyronine (T3) levels, and treatment with levothyroxine may be considered in patients with symptoms, despite limited evidence of therapeutic benefit.
Diagnosis
- SCH is characterized by TSH levels between 4.5 and 10 mIU/L, with normal T4 and T3 levels 1.
- The diagnosis is often made in asymptomatic individuals, but some patients may exhibit symptoms compatible with hypothyroidism, such as fatigue, feeling cold, weight gain, hair loss, and constipation.
Treatment
- Treatment with levothyroxine may be considered in patients with symptoms, but the likelihood of improvement is small, and the decision to treat should be based on clear symptomatic benefit 1.
- The American Thyroid Association recommends measuring thyroid function in all adults beginning at age 35 years and every 5 years thereafter, noting that more frequent screening may be appropriate in high-risk or symptomatic individuals.
- A double-blind RCT reported significant improvement in symptomatic patients with subclinical hypothyroidism treated with levothyroxine compared with placebo, but the study had limitations, and the results may not be generalizable to all patients with SCH 1.
- The majority of studies, including two RCTs, found no improvement in symptoms with levothyroxine therapy in patients with TSH levels lower than 10 mIU/L 1.
Special Considerations
- Subclinical hypothyroidism is associated with poor obstetric outcomes and poor cognitive development in children, and treatment may be considered in these cases 1.
- Patients with Down syndrome may be at higher risk for thyroid dysfunction, and evaluating for symptoms of hypothyroidism can be challenging in these patients 1.
- Clinicians should be aware of subtle signs of thyroid dysfunction, particularly among those at high risk, including the elderly, postpartum women, and those with high levels of radiation exposure 1.
From the Research
Diagnosis of Subclinical Hypothyroidism (SCH)
- Subclinical hypothyroidism is defined as elevated thyroid-stimulating hormone (TSH) levels with normal serum free thyroxine (T4) and triiodothyronine (T3) levels 2, 3, 4, 5, 6.
- The diagnosis of SCH is primarily based on clinical signs and symptoms as well as measurement of TSH concentration 6.
- SCH may progress to overt hypothyroidism in approximately 2-5% cases annually 2.
Treatment of Subclinical Hypothyroidism (SCH)
- Levothyroxine (LT4) monotherapy remains the current standard for management of primary and central hypothyroidism 2, 6.
- Treatment is indicated in patients with TSH >10 mIU/L, pregnant women, and women contemplating pregnancy 2, 4, 6.
- In non-pregnant adults ≤70 years, treatment is clearly indicated if the TSH concentration is >10 mU/l 6.
- Treatment should be considered in symptomatic patients, patients with infertility, and patients with goitre or positive anti-thyroid peroxidase (TPO) antibodies 2.
- 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 2.
- The biochemical treatment goal for T4 replacement in primary hypothyroidism is a TSH level within the reference range (0.4-4.0 mU/l) 6.
Special Considerations
- In older subjects, treatment should be individualised and based on the presence of symptoms, the level of TSH, and initiated at TSH levels ≥10 mIU/L and at low doses to avoid adverse cardiovascular effects from overtreatment 4.
- 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 2.
- T4/liothyronine (T3) combination therapy is still a matter of debate and not recommended as standard therapy, but may be considered in patients with persistence of symptoms, despite optimal T4 treatment, based on expert opinion 6.