Common sx:
- Fatigue, weight gain, cold intolerance
- Depression, dry skin, constipation
- Hair thinning or loss
Associated risk factors:
- Fam hx of autoimmune disease
- Previous thyroid disease or therapy (e.g., radioiodine, thyroidectomy)
- Certain meds (e.g., lithium, amiodarone)

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Examination

General features:
- Dry skin, brittle nails, bradycardia
- Hyporeflexia, slow movement and speech
- Myxoedema (puffy facial features)
- Vitiligo (if autoimmune thyroiditis is present)
Subclinical hypothyroidism:
- Normal T4 with elevated TSH
- Often asymptomatic; sx may be subtle

Note: remember “subclinical” has NOTHING to do with actual sx (see below)

Controversial - eTG and utd diff advice. as per eTG below

If symptomatic commence tx
If asymptomatic, commence tx if TSH >10 (on repeat)
If asymptomatic and TSH 4-10, do TPO and monitor more closely if +ve (q3-6mo), otherwise q12mo. commence if incr TSH or sx develop.

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Management

Overt hypothyroidism:
- Start levothyroxine (thyroxine):
  - Full replacement: 1.6 mcg/kg/day (adjust based on lean body weight)
  - Partial replacement: 25–50 mcg daily for elderly or those with cardiovascular disease
  - Adjust dose every 4–8 weeks until TSH is within target range
Subclinical hypothyroidism:
- TSH >10 mU/L:
  - Commence treatment, even if asymptomatic
- TSH 4–10 mU/L:
  - Assess for thyroid peroxidase antibodies (TPOAbs):
    - TPOAb-positive: Monitor TSH closely and consider treatment if sx develop or TSH rises
    - TPOAb-negative: Monitor TSH 6–12 monthly
- Symptomatic patients: Trial treatment regardless of TSH level
Special considerations:
- Adjust treatment in pregnancy or severe cardiovascular disease (lower starting doses recommended)

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Referral Criteria

Young patients (<18 years)
Pregnancy or planning to conceive
Complex or refractory cases (e.g., poor response to treatment)
Presence of goitre or thyroid nodules
Coexisting endocrine disorders (e.g., type 1 diabetes, Addison’s disease)

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Notes

TPO antibodies:
- Positive in 15% of the general population; does not always indicate the need for treatment unless biochemistry or sx justify
Thyroid US is unnecessary unless a goitre or nodules are palpable
Adjust treatment targets for older patients:
- TSH: 1–5 mU/L for those >60 yrs
- Higher targets for frail or >80 yrs

Hypothyroidism

History

Common symptoms: Weight gain, cold intolerance, depression, fatigue, constipation, hair loss, and dry skin.
Additional symptoms:
- Lethargy, increased sleep, puffy face (often with periorbital edema), husky voice, slow speech.
- Menstrual abnormalities: Menorrhagia or oligomenorrhoea.
- Hyperlipidemia and associated cardiovascular risks.
- Cognitive symptoms: Depression, dementia, psychosis (in severe cases).
- Rare: Myxoedema coma (severe form), psychosis.

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Examination

Signs of hypothyroidism:
- Hyporeflexia, bradycardia, dry skin, brittle nails, hair thinning, and slow movements.
- Neuromuscular signs: Muscle weakness, ataxia, and carpal tunnel syndrome.
- Severe cases: Myxoedema coma, manifesting as hypothermia, hypoventilation, and altered mental status.
- Loss of outer one-third of eyebrows, husky voice, slow speech, and possible goitre (in Hashimoto's thyroiditis).

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Aetiology

Primary Hypothyroidism: Most common cause is chronic autoimmune thyroiditis (Hashimoto’s thyroiditis).
- Often associated with goitre or may present without it in atrophic thyroiditis.
Postpartum Hypothyroidism: Often autoimmune in nature.
Iodine Deficiency: Rare in Australia but common worldwide.
Drug-Induced: E.g., amiodarone, lithium.
Other Causes: Infiltrative diseases, thyroid surgery, radioactive iodine treatment, and congenital hypothyroidism.
Central Causes: Hypothalamic or pituitary dysfunction leading to secondary hypothyroidism.

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Risk Factors

Increased risk in patients with:
Autoimmune diseases (e.g., Type 1 diabetes, rheumatoid arthritis).
Genetic predispositions (e.g., Turner’s and Down syndromes).

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Investigations

Serum TSH and T4: Initial and confirmatory test.
- Elevated TSH and low T4 indicate primary hypothyroidism.
- Normal T4 and elevated TSH suggest subclinical hypothyroidism.
Thyroid Antibodies:
- TPO antibodies for autoimmune thyroiditis.
- Antithyroglobulin antibodies less commonly used, mainly in cancer follow-up.
Additional Tests:
- Lipid profile, FBC (for anemia), ECG, and imaging if structural abnormalities are suspected.

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Management (Including Subclinical and Dosing)

Overt Hypothyroidism: Start with levothyroxine replacement.

Initial dose based on age, comorbidities, and body weight.
Adjust dose every 4-8 weeks to reach target TSH levels.
Usual maintenance dose ranges from 75-125 mcg daily.

Subclinical Hypothyroidism:

Treat if TSH >10 mU/L, or in symptomatic individuals.
Lower TSH thresholds for treatment in younger patients or those with risk factors (e.g., cardiovascular disease).

Special Populations:

Pregnancy: Aim for trimester-specific TSH goals.
Elderly: Aim for conservative TSH targets, consider starting with partial replacement.
Children: Focus on growth and development; regular follow-ups.

Thyroxine Counseling

Take on an empty stomach, 30-60 minutes before breakfast or at bedtime.
Avoid taking with calcium or iron supplements within 4 hours of ingestion.

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Referral Criteria

Indications for referral:

Young patients (<18 years) or pregnant individuals.
Cardiac disease or other endocrine comorbidities.
Goitre or nodules.
Poor response to treatment or need for specialized care (e.g., myxoedema coma).

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Notes:

Medication Considerations:

Levothyroxine should be taken on an empty stomach, 30 minutes before meals or other medications.
Avoid simultaneous intake with calcium, iron, or multivitamins due to reduced absorption.

Adjustments:

Dose adjustments may be necessary with new medications (e.g., OCP, antiepileptics).

Storage: Keep levothyroxine in a cool, dry place, away from direct sunlight.

Special Scenarios:

Myxoedema coma requires emergency treatment with IV thyroxine, steroids, and supportive measures.

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