Hypothyroidism

Urgent Action:

Myxoedema coma is a medical emergency and requires hospitalization in an ICU and initial treatment with special doses of levothyroxine.

Congenital hypothyroidism requires prompt treatment, ideally initiated within first 2 weeks of life

If TSH at newborn screening is greater than 40 milliunits/L, begin levothyroxine therapy immediately after drawing confirmatory serum sample, without waiting for the results

If TSH is 40 milliunits/L or less, delay treatment until results of confirmatory serum sample are available.

Key Facts:

Autoimmune thyroiditis (eg, Hashimoto disease, other chronic thyroiditis) is the most common cause of hypothyroidism in the United States

Diagnosis is suggested by history and physical examination; it is confirmed by measurement of serum TSH and free T₄ levels

Antithyroid (antithyroperoxidase) antibody testing is indicated when evaluating patients with subclinical hypothyroidism or to identify the autoimmune cause of primary hypothyroidism 1 2

Monitor adequacy of levothyroxine replacement by measuring TSH levels in primary hypothyroidism and free T₄ levels in central hypothyroidism 2 3

Treatment of subclinical hypothyroidism (elevated TSH level, normal T₄ level) is recommended in patients with TSH levels higher than 10 milliunits/L 4

Drug therapy uses weight-based dosing with further recommendations for special populations such as pregnant patients, older adults (eg, those aged 65 years or older), and patients with coronary artery disease

Pitfalls

Myxedema coma is a life-threatening condition with cardinal symptoms that are often overlooked (hypothermia with mental status changes or coma)

Laboratory test ordering patterns that rely on TSH level with reflex to T₄ level (for an elevated level of TSH) may miss secondary and tertiary disease

In secondary (central) hypothyroidism, exclude concomitant adrenal insufficiency; when it is present, steroids must be started before T₄ treatment is initiated to avoid precipitating an adrenal crisis

Classification

Causes

Diagnosis