Hyperthyroidism
Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management
Definition
Hyperthyroidism is a condition characterised by excessive production of thyroid hormones (T3 and T4), leading to an increased metabolic rate and systemic effects.
Aetiology
- Graves’ disease: the most common cause, an autoimmune disorder with thyroid-stimulating immunoglobulins (TSI) stimulating the TSH receptor.
- Toxic multinodular goitre: autonomously functioning thyroid nodules producing excess thyroid hormones.
- Toxic adenoma: a single hyperfunctioning thyroid nodule.
- Subacute thyroiditis: transient hyperthyroidism due to thyroid inflammation and hormone release.
- Iodine-induced hyperthyroidism: excessive iodine intake (e.g., contrast media, amiodarone).
- Exogenous thyroid hormone use: excessive levothyroxine intake.
Pathophysiology
- Excess thyroid hormones increase metabolic activity and sympathetic nervous system stimulation.
- In Graves’ disease, autoantibodies stimulate the TSH receptor, leading to thyroid hormone overproduction.
- Toxic nodular goitre results from autonomously functioning thyroid nodules independent of TSH regulation.
Risk Factors
- Family history of thyroid disorders.
- Female sex (higher prevalence in women).
- Smoking (increases risk of Graves’ disease and ophthalmopathy).
- Recent pregnancy (postpartum thyroiditis).
- Excess iodine exposure.
Signs and Symptoms
- General: weight loss despite increased appetite, heat intolerance, sweating.
- Neurological: anxiety, tremors, hyperreflexia.
- Cardiovascular: tachycardia, atrial fibrillation, palpitations.
- Ophthalmological: exophthalmos, lid lag (Graves’ disease).
- Dermatological: pretibial myxoedema (Graves’ disease).
- Thyroid examination: diffuse goitre in Graves’, nodular thyroid in toxic multinodular goitre.
Investigations
- Thyroid function tests: low TSH, elevated free T4 and/or T3.
- Thyroid autoantibodies: TSH receptor antibodies (TRAb) in Graves’ disease.
- Radioiodine uptake scan: increased uptake in Graves’ disease and toxic nodular goitre, decreased uptake in thyroiditis.
- Thyroid ultrasound: useful for assessing nodules.
Management
Patient must be referred urgently to endo.1. Antithyroid Medication:
- Carbimazole: first line treatment, inhibits thyroid hormone synthesis.
- Propylthiouracil (PTU): preferred in pregnancy and thyroid storm.
- Monitor thyroid function tests every 4–6 weeks during treatment.
2. Symptomatic Control:
- Beta blockers (e.g., propranolol): to manage tremors, tachycardia, and anxiety.
3. Radioactive Iodine (RAI) Therapy:
- Used for definitive treatment in Graves’ disease and toxic nodular goitre.
- Contraindicated in pregnancy and breastfeeding.
4. Surgical Management:
- Thyroidectomy: indicated for large goitres, compressive symptoms, or malignancy suspicion.
5. Referral:
- Ophthalmology: if Graves’ orbitopathy is present.
- Surgery: if thyroidectomy is considered.