Working diagnosis for Suzie

Suzie's TSH level of 6.0 mIU/L is elevated (i.e. > 4.0 mIU/L).

My working diagnosis is subclinical thyroiditis.

As Suzie is symptomatic, further investigation is required to confirm the diagnosis.

The next thing I would do is to:

1. Obtain a free T4 level immediately
2. Consider checking TPO antibody
3. Consider offering 3-6 month trial of levothyroxine and continue if symptomatic benefit

Treating patients with mildly elevated TSH (4-10 mU/L):

• The significance and hence the benefits of treating subclinical hypothyroidism remains controversial¹
• If TSH is 4-10 mU/L in an asymptomatic individual, manage as follows;
  • Check serum TSH, free T4 and TPOAb 6-8 weeks later.
  • Offer treatment if the abnormality persists.
• The health impact of subclinical hypothyroidism with mildly elevated levels of TSH (4–10 mU/L) remains uncertain, particularly in older people; treatment or observation are reasonable options².
• In patients with a mildly elevated TSH (up to 10 mU/L), TSH normalises without treatment in over 50% of cases, so treatment need not be offered immediately.

 

¹So, M., MacIsaac, R.J. and Grossmann, M. (2012). Hypothyroidism: Investigation and management. Australian Family Physician, 41(8), 556-562.
view article

²Walsh, J. (2016). Managing thyroid disease in general practice. The Medical Journal of Australia, 205(4), 179-184.
View article

RCPA, (2019). Thyroid disorders
View resource

Thyroid disease in the perinatal period

• Pregnancy is a state of increased thyroid demand (thyroid hormone synthesis is increased by up to 50%)
• Iodine requirements are increased in pregnancy (WHO recommends a daily intake of 250mcg during pregnancy and lactation). Excess iodine can cause fetal hypothyroidism so very large doses (Kelp tablets, Lugol's iodine solution) should be avoided
• Pregnancy specific reference ranges should be used
• Untreated hypothyroidism results in children with a decreased IQ and increases the risk of miscarriage, premature birth, stillbirth, and low birth weight
• Women with pre-existing hypothyroidism need to increase their thyroxine dose by 30% in pregnancy – this equates to 2 additional doses per week on suspicion or confirmation of pregnancy
• TSH and free T4 should be rechecked every 4 weeks for the first half of pregnancy and then again at 26-32 weeks
• After delivery, the thyroxine dose can be reduced to pre-pregnancy levels. If adequately treated through pregnancy, neonatal thyroid function testing is not necessary
• Subclinical hypothyroidism is associated with miscarriage, but not impaired cognitive function. Some clinicians may choose to consider low dose thyroxine replacement but clear guidelines have not been established
• Overt hyperthyoidism in pregnancy is less common and may be due to Graves' disease, a toxic nodule or gestational thyrotoxicosis
• Postpartum thyroiditis is common, affecting 1 in 20 women. Presentation may be hypothyroid (48%), biphasic (hyperthyroidism followed by hypothyroidism) (22%) or isolated hyperthyroidism (30%)
• Postpartum thyroiditis with hyperthyroidism usually occurs 3-6 months postpartum and needs to be differentiated from Graves' disease. Beta blockers can be used for symptomatic management and the thyrotoxic phase tends to self-limit.
• Postpartum thyroiditis resulting in hypothyroidism usually occurs at 6-12 months postpartum. Thyroxine is indicated for those trying to conceive or those experiencing symptoms. A high proportion of women will recover. An attempt to wean thyroxine 6-12 months after the final pregnancy should be made. Long-term follow up with annual TFT is recommended

Department of Health and Aged Care. (2019). Thyroid dysfunction
view website

PatientPlus. (2016). Thyroid Disease In Pregnancy
View website

Hypothyroidism

• Occurs in about 5% of the adult population; women to men 5:1 (i.e. up to 8% women and 2% of men)

• Initial screening is performed by measuring TSH

• Subclinical hypothyroidism (mild thyroid failure) is the most common. Raised TSH but normal T4

• Overt hypothyroidism: Raised TSH and decreased T4

• Secondary hypothyroidism: Normal TSH and low T4. Suggests a pituitary or hypothalamic cause or a severe non-thyroidal illness

• Autoimmune chronic lymphocytic thyroiditis is the most common cause in Australia (characterised by raised circulating levels of thyroid peroxidase antibody)

• Symptoms and signs are often mild or subtle

• Thyroid function tests are needed to confirm the diagnosis

• If serum TSH level is raised, free T4 and thyroid peroxidase antibody should be measured (this is the only test needed to confirm the diagnosis of autoimmune thyroiditis)

• A diagnosis of hypothyroidism in itself is not an indication for thyroid imaging. Thyroid ultrasound is only indicated to evaluate structural thyroid abnormalities (e.g. palpable thyroid nodules)

• Replacement therapy with thyroxine is the basis of therapy (1.6μg/kg lean body weight daily, taken on an empty stomach)

• Measurement of both TSH and free T4 is required to optimise therapy

• The minimum period to achieve a stable concentration with thyroxine is 2 months, (thyroid function tests should not normally be requested before this period elapses)

• Optimal dose for long-term therapy: assessed through thyroid function tests and clinical findings.

• Optimal dose of thyroxine should result in a non-elevated TSH level in the detectable range (preferably within the reference range)

• Once a patient is stabilised on therapy, TSH readings should be taken at least annually

• Free T3 testing is not necessary in the assessment of hypothyroidism or during routine thyroxine replacement