Hyperthyroidism

Overview – Hyperthyroidism

Hyperthyroidism refers to excessive secretion of thyroid hormones, leading to widespread hypermetabolic effects across multiple organ systems. Graves’ disease remains the most common cause globally, with other causes including toxic multinodular goitre and subacute thyroiditis. Prompt diagnosis and treatment are essential to prevent severe complications such as thyrotoxic storm.

Definition

• Hyperthyroidism: Excess thyroid hormone secretion (T3, T4) causing increased basal metabolic rate and sympathetic activity.

Aetiology

Autoimmune

• Graves’ disease:
  • Thyroid-stimulating antibodies (TsAb) mimic TSH.
  • Stimulate T3/T4 overproduction.

Nodular

• Toxic multinodular goitre:
  • Autonomous thyroid nodules develop within a pre-existing goitre.
  • Independently secrete thyroid hormones.

Subacute Thyroiditis

• Post-URTI Subacute (“De-Quervain’s”) Thyroiditis:
  • Transient hyperthyroid phase followed by hypothyroid or euthyroid state.

Pathophysiology

• ↑ Basal metabolic rate
• ↑ Sympathetic sensitivity
• ↑ Thermogenesis → Heat intolerance
• If Graves’ disease: characteristic exophthalmos and goitre

Clinical Features

General

• Fatigue
• Heat intolerance

Cardiovascular

• Tachycardia
• Palpitations
• Atrial fibrillation (particularly in elderly)
• Cardiomegaly
• Congestive heart failure

Gastrointestinal

• Weight loss despite increased appetite
• Thirst
• Increased bowel frequency, diarrhoea

Neurological

• Sympathetic overactivity:
  • Fine tremor
  • Irritability, anxiety, insomnia
• Proximal myopathy and muscle wasting

Ocular

• Exophthalmos (proptosis; specific to Graves’)
• Lid lag
• Wide, staring gaze

Dermatological

• Acropachy (digital clubbing, swelling of fingers and toes)
• Fine hair, alopecia
• Warm, flushed, sweaty skin
• Vitiligo
• Plummer’s nails (onycholysis)

Musculoskeletal

• Increased bone resorption → Osteoporosis

Haematological

• Lymphadenopathy (especially in Graves’)

Other

• Menorrhagia
• Pretibial myxoedema

Investigations

• TSH: suppressed
• T3/T4: elevated
• Autoimmune screening (Graves):
  • Thyroid-stimulating immunoglobulins (TSI/TsAb)

Management

Medical

• Anti-thyroid drugs:
  • Carbimazole (first-line)
  • Propylthiouracil (alternative, especially in pregnancy)

Radioactive Iodine Therapy

• Iodine-125 to destroy thyroid tissue.
• Risk of inducing hypothyroidism.

Surgical

• Partial or total thyroidectomy.
• Used for refractory cases, large goitres, or compressive symptoms.

Complications

Thyrotoxic Storm (Thyroid Crisis)

• Life-threatening hyperthyroid emergency with ~50% mortality if untreated.

Triggers

• Infection, trauma, surgery, myocardial infarction, heart failure.

Clinical Features

• Extreme fever
• Severe tachycardia and arrhythmias
• Hypotension, vascular collapse
• Heart failure, pulmonary oedema
• Vomiting, diarrhoea
• Confusion, delirium, coma

Differentials

• Sepsis
• Phaeochromocytoma
• Malignant hyperthermia

Laboratory Findings

• Markedly ↑ T3/T4
• Markedly ↓ TSH
• Leukocytosis
• Hypercalcaemia
• Elevated liver enzymes

Management

• Treat precipitating cause.
• Supportive care (ABCs, fluid resuscitation, cooling measures).
• Beta-blockers (propranolol) to control sympathetic symptoms.
• Antithyroid medications (high-dose carbimazole or propylthiouracil).
• Steroids (hydrocortisone) to reduce conversion of T4 to T3.
• Iodine solution (Lugol’s iodine) in select cases after antithyroid pretreatment.

Summary – Hyperthyroidism

Hyperthyroidism describes excess secretion of thyroid hormones, most commonly due to Graves’ disease. It causes multi-system hypermetabolic symptoms and can progress to life-threatening thyrotoxic storm if not promptly managed. For a broader context, see our Endocrine Overview page.