Summary

Hypothyroidism is a clinical syndrome resulting from deficiency of thyroid hormones (T3 and T4). The most common cause in iodine-sufficient areas is autoimmune thyroiditis (Hashimoto's disease). Other causes include post-treatment (radioiodine, surgery), medications (amiodarone, lithium), and central causes (pituitary or hypothalamic disease). Patients present with fatigue, weight gain, cold intolerance, constipation, and dry skin. Diagnosis is made biochemically with elevated TSH and low free T4. Treatment is lifelong levothyroxine replacement, titrated to normalise TSH. Special considerations apply to the elderly, patients with cardiovascular disease, and pregnant women.

Key Facts

• Definition: Clinical syndrome due to thyroid hormone deficiency
• Incidence: Prevalence 2-5%; subclinical 4-10%; more common in women and elderly
• Demographics: F:M 5-8:1; increases with age
• Pathognomonic: Elevated TSH + low fT4 + compatible symptoms
• Gold Standard Investigation: Serum TSH, free T4
• First-line Treatment: Levothyroxine (T4) replacement
• Prognosis: Excellent with treatment; lifelong therapy required

Clinical Pearls

Cardiac Pearl: In elderly patients or those with cardiac disease, start levothyroxine at LOW doses (25-50mcg) to avoid precipitating angina or arrhythmias.

TSH Timing Pearl: Check TSH 6-8 weeks after dose changes - it takes this long for TSH to stabilise. Take levothyroxine fasting before blood test.

Subclinical Pearl: Treat subclinical hypothyroidism if TSH greater than 10, symptomatic, or pregnant/planning pregnancy. Watch and wait if TSH less than 10 and asymptomatic.

Drug Pearl: Many drugs affect thyroid function or levothyroxine absorption: amiodarone, lithium, iron, calcium, PPI.

Pregnancy Pearl: Thyroid requirements increase by 25-50% in pregnancy. Adjust levothyroxine early and monitor closely.

Why This Matters Clinically

Hypothyroidism is extremely common and easily treated, but often missed. Symptoms are non-specific and attributed to aging or depression. A high index of suspicion and simple blood tests enable diagnosis and transformative treatment.

General Inspection

• Appearance: puffy face, periorbital oedema
• Voice: hoarse, slow speech
• Affect: flat, slow mentation
• Weight: often increased
• Hair: thin, coarse, loss of lateral eyebrows

Hands

• Dry, cool skin
• Carpal tunnel syndrome signs
• Slow pulse

Neck

• Goitre (may be diffuse in Hashimoto's or absent)
• Thyroidectomy scar

Cardiovascular

• Bradycardia
• Hypotension
• Pericardial effusion (rare, severe cases)

Neurological

• Delayed relaxation of deep tendon reflexes
• Proximal myopathy
• Cerebellar signs (rare)

Skin

• Dry, rough, cool
• Yellow tinge (carotenaemia)
• Non-pitting oedema (myxoedema)

Response to Treatment

• Symptoms improve within 2-4 weeks
• Full biochemical and clinical response: 6-12 weeks
• Weight loss typically modest (2-4 kg)
• Lipid profile improves

Long-Term Outlook

• Excellent prognosis with treatment
• Lifelong replacement therapy required
• Annual monitoring usually sufficient once stable
• No increased mortality if well-controlled

Key Guidelines

1. ATA/AACE Guidelines for Hypothyroidism — Garber JR et al. Endocr Pract. 2012;18(6):988-1028. PMID: 23246686

2. NICE CKS: Hypothyroidism — Updated regularly

3. ETA Guidelines for Subclinical Hypothyroidism — Biondi B et al. Eur Thyroid J. 2021

4. ATA Guidelines for Thyroid Disease in Pregnancy — Alexander EK et al. Thyroid. 2017;27(3):315-389. PMID: 28056690

Key Studies

Levothyroxine Bioequivalence

• Generic levothyroxine is bioequivalent
• Maintain same brand if possible for consistency

Subclinical Hypothyroidism and Cardiovascular Risk

• TSH greater than 10 associated with increased CV events
• Lower TSH elevations uncertain benefit from treatment
• PMID: 20231456

What is hypothyroidism?

Your thyroid gland, which sits in your neck, isn't making enough thyroid hormone. This hormone controls your metabolism - how your body uses energy.

What causes it?

The most common cause is an autoimmune condition called Hashimoto's thyroiditis, where your immune system attacks your thyroid. Other causes include previous thyroid treatment or certain medications.

What is the treatment?

You'll take a daily thyroid hormone tablet (levothyroxine) to replace what your body isn't making. It's usually taken first thing in the morning before breakfast.

Will I take it forever?

Usually yes - most causes of hypothyroidism are permanent. The good news is it's a simple, safe, and effective treatment.

How will I be monitored?

Blood tests to check your thyroid levels every 6-8 weeks until stable, then usually once a year.

Important tips

• Take your tablet at the same time each day
• Don't take it with calcium, iron tablets, or antacids (wait 4 hours)
• Tell your doctor if you become pregnant - dose often needs to increase

Viva Points

"Hypothyroidism is thyroid hormone deficiency, most commonly due to autoimmune Hashimoto's thyroiditis. Diagnosis: elevated TSH + low fT4. Treat with levothyroxine - start low in elderly/cardiac patients. Monitor TSH 6-8 weeks after dose changes. Target TSH 0.5-2.5. Subclinical hypothyroidism: treat if TSH greater than 10 or symptomatic."

Key Examination Points

• Slow, hoarse voice
• Periorbital puffiness
• Dry, cool skin
• Bradycardia
• Delayed relaxation of deep tendon reflexes
• Goitre (may be absent)

Common Mistakes

• ❌ Starting full replacement dose in elderly/cardiac patients
• ❌ Checking TSH too soon after dose change (need 6-8 weeks)
• ❌ Forgetting to check fT4 when TSH is mildly elevated
• ❌ Not recognising drug-induced causes (amiodarone, lithium)
• ❌ Not increasing dose in pregnancy

Differentials

• Depression
• Anaemia
• Chronic fatigue syndrome
• Heart failure
• Dementia (in elderly)

Last Reviewed: 2026-01-01 | MedVellum Editorial Team