Thyroid Disease: Hypothyroidism, Hyperthyroidism and Thyroid Nodules

The thyroid gland — a butterfly-shaped structure wrapped around the front of the trachea (windpipe) in the neck — produces thyroid hormones (T3 and T4) that regulate metabolism in every cell of the body. Thyroid disorders are among the most prevalent endocrine conditions worldwide, affecting an estimated 1 in 10 adults, with women affected approximately 5–8 times more often than men.

Thyroid disease encompasses a spectrum: underactivity (hypothyroidism), overactivity (hyperthyroidism), structural abnormalities (nodules, goitre), and malignancy (thyroid cancer). Fortunately, all of these conditions are highly treatable when correctly diagnosed.

How the Thyroid Works

The thyroid hormone system operates through a feedback loop:

1. The hypothalamus releases thyrotropin-releasing hormone (TRH)
2. TRH stimulates the pituitary to release thyroid-stimulating hormone (TSH)
3. TSH drives the thyroid to produce thyroxine (T4) and triiodothyronine (T3)
4. Rising T3/T4 levels feed back to suppress TRH and TSH

TSH is the most sensitive and clinically important thyroid test — it amplifies small changes in circulating thyroid hormone levels. A raised TSH indicates the pituitary is working harder to drive an underactive thyroid (hypothyroidism); a suppressed TSH indicates an overactive thyroid is suppressing pituitary output (hyperthyroidism).

Thyroid hormones regulate:

• Basal metabolic rate and thermogenesis
• Heart rate and cardiac output
• Gastrointestinal motility
• Brain development (critical in foetal life and infancy)
• Bone turnover
• Reproductive function and fertility
• Lipid metabolism (T4 deficiency raises LDL cholesterol)

Hypothyroidism — Underactive Thyroid

What Is Hypothyroidism?

Hypothyroidism occurs when the thyroid gland produces insufficient thyroid hormone, causing the metabolism to slow. It affects approximately 5% of the general population (2–4% overt; up to 10% subclinical), and is significantly more common in women and older adults.

Causes

Hashimoto's thyroiditis (autoimmune thyroiditis) — by far the most common cause of hypothyroidism in iodine-sufficient countries. The immune system produces antibodies (anti-TPO and anti-thyroglobulin antibodies) that attack and progressively destroy thyroid tissue. The gland typically becomes enlarged (goitre) initially, then atrophies. Strongly associated with other autoimmune diseases (type 1 diabetes, coeliac disease, vitiligo, Addison's disease).

Post-radioiodine or surgical hypothyroidism — common after radioiodine treatment for hyperthyroidism or after thyroidectomy; the intended or inevitable outcome of these treatments.

Iodine deficiency — the most common cause of hypothyroidism globally; rare in developed countries with iodine-fortified salt.

Medications — amiodarone (heart drug containing 37% iodine), lithium, interferon-alpha, and checkpoint immunotherapy drugs can cause hypothyroidism.

Central hypothyroidism — pituitary or hypothalamic failure to produce TSH or TRH (rare); TSH is paradoxically low or normal despite low thyroid hormones.

Symptoms of Hypothyroidism

Symptoms develop insidiously over months to years — patients often attribute them to ageing or stress:

• Fatigue and lethargy — the most common complaint; profound, persistent tiredness
• Weight gain — despite unchanged or reduced appetite (reduced metabolic rate)
• Cold intolerance — feeling cold when others are comfortable
• Dry skin, dry hair, and hair loss — hair becomes coarse and brittle; diffuse hair thinning
• Constipation — slowed GI motility
• Bradycardia — slow heart rate; may cause palpitations of a different kind (awareness of the slow beat)
• Depression and cognitive slowing — "brain fog," poor memory, difficulty concentrating; hypothyroidism is an important reversible cause of depression
• Muscle weakness and aches — myopathy; elevated CK in severe cases
• Menstrual irregularities — heavy periods (menorrhagia); infertility
• Raised LDL cholesterol — reduced cholesterol clearance; accelerates atherosclerosis
• Myxoedema — puffiness of the face, hands, and legs from glycosaminoglycan deposition in tissues; non-pitting

Severe/untreated hypothyroidism:

• Myxoedema coma — life-threatening; altered consciousness, hypothermia, bradycardia; precipitated by cold exposure, infection, or sedatives in elderly hypothyroid patients

Diagnosis and Treatment of Hypothyroidism

Diagnosis: elevated TSH (>4.5 mU/L) with low free T4. Anti-TPO antibodies confirm Hashimoto's. Subclinical hypothyroidism: elevated TSH with normal free T4.

Treatment — Levothyroxine (T4 replacement):

• Oral synthetic thyroxine; taken once daily on an empty stomach (30–60 minutes before breakfast), at least 4 hours away from calcium, iron, or antacids that impair absorption
• Dose titrated to normalise TSH (target 0.5–2.5 mU/L for most patients; slightly higher in the elderly)
• Monitored with TSH every 6–12 months once stable
• Lifelong treatment in permanent hypothyroidism
• Occasional patients feel better on combined T4/T3 therapy — liothyronine added in small doses

Subclinical hypothyroidism: treatment recommended when TSH >10 mU/L, in pregnancy, with symptoms, or in those with raised cardiovascular risk.

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Hyperthyroidism — Overactive Thyroid

What Is Hyperthyroidism?

Hyperthyroidism occurs when the thyroid produces excess thyroid hormone, accelerating the metabolism. It affects approximately 1.2% of the population.

Causes

Graves' disease — the most common cause (80% of cases); an autoimmune condition in which IgG antibodies (TSI — thyroid-stimulating immunoglobulins) bind and activate the TSH receptor, permanently stimulating thyroid hormone production. Associated with Graves' ophthalmopathy (eye disease) in 25–50% — exophthalmos (bulging eyes), eye irritation, double vision.

Toxic multinodular goitre (Plummer's disease) — multiple autonomous thyroid nodules producing thyroid hormone independently of TSH; common in older patients in iodine-deficient areas.

Toxic adenoma — single autonomous nodule ("hot nodule") secreting excess hormone.

Thyroiditis — transient hyperthyroidism from release of stored thyroid hormone during autoimmune (post-partum, de Quervain's), drug-induced, or amiodarone-related thyroid inflammation. Followed by hypothyroid phase, then usually recovery.

Symptoms of Hyperthyroidism

• Weight loss despite increased appetite and food intake
• Heat intolerance and excessive sweating
• Palpitations and rapid heart rate (tachycardia); atrial fibrillation in older patients
• Tremor of the hands (fine tremor at rest)
• Anxiety, irritability, emotional lability — nervousness, restlessness, poor concentration
• Fatigue and weakness — proximal muscle weakness
• Diarrhoea — increased GI motility
• Menstrual irregularities — oligomenorrhoea; infertility
• Hair thinning
• Goitre — enlarged thyroid gland visible or palpable in the neck
• Graves' ophthalmopathy (Graves' disease only): proptosis, lid retraction, periorbital oedema, restricted eye movement, diplopia — managed by an oculoplastic/orbital specialist
• Thyroid storm — life-threatening hyperthyroid crisis precipitated by surgery, infection, or radioiodine; extreme tachycardia, hyperthermia, cardiac arrhythmia, and altered consciousness

Diagnosis

Suppressed TSH (<0.1 mU/L) with elevated free T4 and/or free T3. TSI antibodies confirm Graves' disease. Thyroid ultrasound assesses goitre size and nodules. Thyroid scintigraphy (radioiodine uptake scan) distinguishes Graves' from thyroiditis (high uptake) and toxic nodule (focal hot nodule).

Treatment of Hyperthyroidism

Antithyroid drugs (ATDs):

• Carbimazole (UK/Europe) or methimazole (US); propylthiouracil (PTU — preferred in first trimester pregnancy)
• Block thyroid hormone synthesis; typically normalise thyroid function within 4–8 weeks
• Used as initial treatment in most cases; 12–18 months for Graves' disease (30–40% achieve remission after stopping)
• Side effects: rash, agranulocytosis (rare but serious — stop immediately if fever/sore throat; check white cell count)
• Beta-blockers (propranolol, atenolol) control adrenergic symptoms (palpitations, tremor) while awaiting ATD effect

Radioiodine (I-131):

• Oral dose of radioactive iodine; selectively destroys thyroid tissue
• Definitive treatment; intentionally causes hypothyroidism (then treated with levothyroxine)
• Preferred for older patients, large goitres, relapsed Graves'; avoid in active Graves' ophthalmopathy and pregnancy

Thyroidectomy (surgical removal):

• Total thyroidectomy for Graves' with very large goitre, ophthalmopathy, or patient preference; toxic multinodular goitre; thyroid nodule with concern for malignancy
• Requires pre-operative euthyroid state; risks: recurrent laryngeal nerve injury, hypoparathyroidism (low calcium post-operatively)

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Thyroid Nodules and Thyroid Cancer

Thyroid nodules are extremely common — present in approximately 50–70% of adults on ultrasound — but the vast majority (>95%) are benign. However, approximately 5–10% of thyroid nodules are malignant.

Risk factors for malignancy: age <20 or >70; male sex; history of head/neck radiation; family history of thyroid cancer; nodule features on ultrasound (irregular margins, microcalcifications, taller-than-wide shape, hypoechogenicity, lymph node involvement).

Investigation of Thyroid Nodules

Thyroid ultrasound — the primary investigation. Classifies nodules using validated risk stratification systems (TIRADS or ACR-TIRADS in the US; UK-TIRADS) assigning risk categories based on ultrasound features. Guides decision to biopsy.

Fine-needle aspiration cytology (FNAC) — ultrasound-guided sampling of cells from the nodule. Results classified by Bethesda system (I–VI); Category IV–VI requires surgical consideration.

Molecular testing — for indeterminate cytology (Bethesda III/IV): Afirma, ThyroSeq, or Thyroseek panels analyse gene mutations (BRAF, RAS, PAX8-PPAR, RET-PTC) to refine malignancy probability and guide surgery decisions.

Thyroid Cancer

• Papillary thyroid cancer (PTC) — most common (80%); excellent prognosis; 20-year survival >95%; treated by thyroidectomy ± radioiodine ablation
• Follicular thyroid cancer — second most common; good prognosis; spreads via blood (bone, lung) rather than lymph nodes
• Medullary thyroid cancer — arises from calcitonin-secreting C cells; 25% hereditary (MEN2); calcitonin is a tumour marker
• Anaplastic thyroid cancer — rare; aggressive; median survival <6 months despite treatment

Thyroid Care in China

China's endocrinology and thyroid surgery centres offer:

• Thyroid assessment: TSH, free T4/T3, antibody panel (anti-TPO, anti-Tg, TSI for Graves'), and high-resolution thyroid ultrasound
• Ultrasound-guided FNAC: experienced cytopathologists interpreting with Bethesda classification; molecular testing available at leading centres
• High-volume thyroidectomy: China's top thyroid surgeons perform thousands of procedures annually — total thyroidectomy, hemithyroidectomy, and central/lateral neck dissection for thyroid cancer; robotic and endoscopic approaches at specialist centres
• Graves' disease management: antithyroid drug titration, radioiodine therapy, and surgical thyroidectomy — all modalities available
• Graves' ophthalmopathy clinic: integrated endocrinology and oculoplastic management of thyroid eye disease
• Cost: care in China is generally less expensive than UK private treatment, but the hospital prices each case individually — ask us for the written quote before you commit.
• Full English care navigation from assessment through surgery and post-operative follow-up

Contact a ChinaMedicalTour care navigator to arrange a thyroid assessment, nodule evaluation, or surgical consultation.

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Medical content based on MSD Manuals and international thyroid guidelines (ETA, ATA). Evidence reviewed 2025.