Thyroid Disease: Hypothyroidism, Hyperthyroidism and Thyroid Nodules

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). Many thyroid conditions can be treated effectively, but treatment options and prognosis depend on the diagnosis; aggressive thyroid cancers can be difficult to treat.

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 an important initial test for suspected primary thyroid dysfunction. A raised TSH may suggest primary hypothyroidism, while a suppressed TSH may suggest hyperthyroidism. Results need interpretation with free T4 (and T3 when indicated), symptoms and clinical context. Pituitary or hypothalamic disease can cause hypothyroidism with low or inappropriately normal TSH.

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. Hypothyroidism is more common in women and older adults; prevalence estimates need a defined population and diagnostic criteria.

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 — may follow radioiodine treatment or thyroid surgery. Removing the whole gland requires lifelong thyroid-hormone replacement; after partial removal, the remaining thyroid may still produce enough hormone.

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 of primary hypothyroidism: TSH above the laboratory reference range with low free T4. Anti-TPO antibodies support an autoimmune cause when interpreted with history, examination and thyroid-function tests; a positive result alone is not a complete diagnostic assessment. Subclinical hypothyroidism means TSH above the reference range 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 adjusted using thyroid-function tests and symptoms; for primary hypothyroidism, aim for TSH within the laboratory reference range and individualise the target, avoiding overtreatment
• Monitored with TSH every 6–12 months once stable
• Lifelong treatment in permanent hypothyroidism
• Combination T4/T3 therapy is not routine treatment; persistent symptoms warrant clinical reassessment and specialist discussion of uncertain benefits and risks.

Subclinical hypothyroidism: a persistently raised TSH of 10 mU/L or higher can support treatment consideration in nonpregnant adults after repeat testing; lower elevations with symptoms may warrant a monitored trial in selected people. Age, thyroid antibodies and individual risks matter; symptoms or cardiovascular risk alone do not make treatment automatic. Pregnancy requires pregnancy-specific assessment and treatment thresholds.

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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, stimulating excessive 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 — destructive inflammation can release stored thyroid hormone, causing transient thyrotoxicosis rather than increased hormone production. Examples include post-partum thyroiditis, subacute painful (de Quervain's) thyroiditis, and some drug-related destructive forms. A hypothyroid phase may follow, but the course and recovery vary; thyroid-function follow-up is needed.

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 (shakiness)
• 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

Low TSH with elevated free T4 and/or free T3 suggests thyrotoxicosis. Determining the cause distinguishes excess hormone production from leakage in destructive thyroiditis; TSH-receptor antibody testing, including TSI, can help confirm Graves' disease in the clinical context. Thyroid ultrasound assesses goitre size and nodules. Thyroid scintigraphy (radioiodine uptake scan), when appropriate, may help distinguish diffuse increased uptake in Graves' disease, low uptake in destructive thyroiditis, and focal increased uptake in a toxic 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
• A 12–18-month course may be selected for Graves' disease; treatment choice and follow-up depend on the cause, likelihood of remission and individual circumstances. Antithyroid drugs do not treat hormone leakage in destructive thyroiditis.
• 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
• May cause hypothyroidism requiring levothyroxine; the intended result and risk differ between Graves' disease and autonomous toxic nodules.
• Suitability depends on the cause, goitre features, eye disease and individual circumstances. Radioiodine is not used during pregnancy or breastfeeding; active Graves’ eye disease requires specialist assessment.

Thyroidectomy (surgical removal):

• Surgery and its extent depend on the diagnosis, goitre or compression, cancer concern, other treatment options and patient preferences. Total thyroidectomy may be selected for Graves' disease or toxic multinodular goitre; a single toxic nodule may instead be treated with hemithyroidectomy.
• 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 most are benign, but a minority are malignant and need clinical evaluation.

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 may help refine cancer risk when thyroid-nodule cytology is indeterminate (Bethesda III/IV). Methods vary: tests may analyse gene-expression patterns or DNA/RNA alterations, rather than all being mutation-only panels. The treating team interprets the selected test alongside the clinical, ultrasound and cytology findings when discussing next steps.

Thyroid Cancer

• Papillary thyroid cancer (PTC) — the most common thyroid cancer; prognosis is often favourable but depends on disease extent and risk. Management is risk-based and may include surgery and, in selected patients, radioiodine.
• 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 and highly aggressive; prognosis is generally poor, but outcomes vary with disease extent and treatment. Molecular testing may identify targeted treatment options for eligible patients; historical survival estimates are not a prognosis for every patient.

Thyroid Care in China

China's endocrinology and thyroid surgery centres offer:

• Thyroid assessment: ask the treating team which thyroid-function tests, antibodies and ultrasound are indicated for the individual case.
• Ultrasound-guided FNAC: confirm whether biopsy is indicated, the reporting system used and whether any proposed molecular test is available at the chosen hospital.
• Thyroid surgery: discuss the proposed extent and approach, the surgeon's relevant experience, and individual benefits and risks; do not assume a particular technique or procedure volume.
• Graves' disease management: discuss which drug, radioiodine or surgical options are suitable and actually offered by the chosen team.
• Thyroid eye disease: confirm access to the relevant endocrinology and eye specialists if needed.
• Cost: obtain the hospital's current written itemised quote and confirm what it includes before committing; no general saving against another country's treatment is assured.
• Language support: confirm directly which hospital appointments, documents and follow-up are available in English and what separate coordination support covers.

Contact a PriumCare 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.

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Targeted editorial source check — 26 October 2026: Only the treatment/prognosis reassurance, hypothyroidism prevalence wording, thyroiditis classification, hand-tremor description, scintigraphy uptake patterns and benign/malignant nodule wording were checked against NCI thyroid cancer information, NIDDK hypothyroidism information, ATA information on thyroiditis, hyperthyroidism and nodules, and the AAFP uptake-pattern table. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.

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Targeted editorial source check — 26 October 2026: Only TSH interpretation, the role of anti-TPO antibodies, selection for subclinical-hypothyroidism treatment, thyroid function after surgery, levothyroxine targets and radioiodine safety/selection wording were checked against ATA thyroid-test information, NIDDK Hashimoto information, NICE NG145 recommendations, ATA pregnancy information, ATA surgery information and NIDDK hyperthyroidism information. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.

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Targeted editorial source check — 26 October 2026: Only the anaplastic thyroid cancer prognosis sentence was checked against NCI thyroid cancer treatment information and ATA anaplastic thyroid cancer information. This is not a whole-article medical review, does not verify the other thyroid cancer statistics and retains the original publication date.

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Targeted editorial source check — 26 October 2026: The cause-specific thyroiditis, testing and treatment wording above was checked against ATA thyroiditis information, ATA radioiodine information, ATA toxic-nodule information, NICE NG145 and NCI thyroid cancer information. Unsupported general access, price-comparison and language claims were qualified for hospital-specific confirmation. This is not a whole-article medical review or verification of every retained statistic, hospital capability or price; the original publication date is retained.

Scoped editorial source check — 26 October 2026: The thyroid molecular-testing methods statement above were checked against the sources below. This limited correction is not a whole-article medical review.

• https://pmc.ncbi.nlm.nih.gov/articles/PMC7729582/
• https://www.cancer.gov/research/participate/clinical-trials-search/v?id=NCI-2024-00287

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Targeted editorial source check — 26 October 2026: Only the Graves antibody-stimulation wording was checked against American Thyroid Association information. Graves hyperthyroidism may enter remission; receptor stimulation is not necessarily permanent. This is not a whole-article medical review, does not verify other retained statistics or treatment statements and retains the original publication date.