Thyroid Disorders: A PLAB 1 Focus
This module covers key aspects of thyroid disorders relevant to the PLAB 1 exam, focusing on common conditions, diagnostic approaches, and management principles within the UK context.
Introduction to the Thyroid Gland
The thyroid gland is a vital endocrine organ located in the neck, responsible for producing hormones that regulate metabolism, growth, and development. Its primary hormones are thyroxine (T4) and triiodothyronine (T3), which are regulated by the pituitary gland's thyroid-stimulating hormone (TSH).
Common Thyroid Disorders
Thyroid disorders can broadly be classified into those causing overactivity (hyperthyroidism) and underactivity (hypothyroidism), as well as structural abnormalities like goitres and nodules.
Hypothyroidism
Hypothyroidism occurs when the thyroid gland doesn't produce enough thyroid hormones. The most common cause in the UK is Hashimoto's thyroiditis, an autoimmune condition.
Hashimoto's thyroiditis.
Symptoms of hypothyroidism are often insidious and can include fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, and depression. In severe cases, it can lead to myxoedema coma.
Hyperthyroidism
Hyperthyroidism, or overactive thyroid, occurs when the thyroid gland produces too much thyroid hormone. The most common cause is Graves' disease, another autoimmune condition.
Graves' disease.
Symptoms of hyperthyroidism include weight loss despite increased appetite, heat intolerance, palpitations, tremor, anxiety, and frequent bowel movements. Ocular manifestations, such as exophthalmos, are characteristic of Graves' disease.
Thyroid Nodules and Goitre
Thyroid nodules are lumps within the thyroid gland, and a goitre is an enlargement of the thyroid gland. While many nodules and goitres are benign, they require investigation to rule out malignancy.
Diagnosis of Thyroid Disorders
Diagnosis relies on a combination of clinical assessment, blood tests, and sometimes imaging.
| Test | Hypothyroidism | Hyperthyroidism |
|---|---|---|
| TSH | High | Low |
| Free T4 | Low | High |
| Free T3 | Low (often) | High |
Antibody testing (e.g., anti-TPO, TRAb) is crucial for diagnosing autoimmune thyroid diseases. Ultrasound is often used to assess thyroid nodules and goitres.
Management Principles (UK Guidelines)
Management aims to restore normal thyroid hormone levels and address the underlying cause.
Hypothyroidism Management
Treatment involves lifelong hormone replacement therapy with levothyroxine (synthetic T4). Dosing is adjusted based on TSH levels, aiming for a TSH within the normal reference range. Regular monitoring is essential.
Levothyroxine is typically taken once daily on an empty stomach, at least 30 minutes before breakfast, to ensure optimal absorption.
Hyperthyroidism Management
Treatment options include:
- Antithyroid drugs: Carbimazole or propylthiouracil (PTU) to reduce hormone production. PTU is often preferred in the first trimester of pregnancy.
- Radioactive iodine therapy: To destroy overactive thyroid tissue.
- Surgery: Thyroidectomy, usually for large goitres, compressive symptoms, or suspected malignancy.
The feedback loop regulating thyroid hormone production involves the hypothalamus, pituitary gland, and thyroid gland. TRH from the hypothalamus stimulates TSH release from the pituitary, which in turn stimulates T4 and T3 production by the thyroid. High levels of T4/T3 inhibit TRH and TSH release, while low levels stimulate them. This negative feedback system maintains hormonal balance.
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Management of Nodules and Goitre
Management depends on the size, symptoms, and suspicion of malignancy. Fine-needle aspiration (FNA) cytology is used to assess suspicious nodules. Surgery may be indicated for compressive symptoms, cosmetic concerns, or malignancy.
Thyroid Emergencies
Thyroid emergencies are rare but life-threatening conditions requiring prompt recognition and management.
Thyroid Storm
A severe, life-threatening exacerbation of hyperthyroidism, characterized by fever, tachycardia, altered mental status, and often gastrointestinal symptoms. Management involves aggressive medical treatment with antithyroid drugs, beta-blockers, iodine, and corticosteroids.
Myxoedema Coma
The most severe form of hypothyroidism, presenting with hypothermia, bradycardia, hypotension, hypoventilation, and altered consciousness. Management involves intravenous levothyroxine and supportive care, including respiratory support and warming.
Thyroid storm and myxoedema coma.
Learning Resources
The official UK guidelines from the National Institute for Health and Care Excellence (NICE) providing comprehensive recommendations on the assessment and management of thyroid disease.
An overview of thyroid disorders from the Endocrine Society, offering patient-friendly information on causes, symptoms, and treatments.
A detailed clinical overview of hypothyroidism, including diagnosis, management, and complications, aimed at healthcare professionals.
A comprehensive clinical guide to hyperthyroidism, covering its various causes, diagnostic approaches, and treatment strategies.
Information from the NHS website about thyroid cancer, including symptoms, causes, diagnosis, and treatment options.
Provides accessible information and support for individuals affected by thyroid disorders, with a focus on patient experience and advocacy.
Patient-facing information from the Royal College of Physicians explaining thyroid disease in a clear and understandable manner.
A comprehensive medical resource for healthcare professionals, offering in-depth information on thyroid disorders, including epidemiology, pathophysiology, and management.
Offers patient-friendly explanations of thyroid function and common thyroid conditions, with resources for support and information.
A visual explanation of the anatomy and physiology of the thyroid gland, helpful for understanding its function and the basis of thyroid disorders.