30. Goitre and special forms of goitre

1. Definition

• Goitre (struma) → enlargement of the thyroid gland, of any cause
• Non-toxic goitre → benign, non-inflammatory enlargement without hyperthyroidism
• Endemic goitre → goitre in > 10% of a population; caused by iodine deficiency

2. Epidemiology

• More than 2 billion people exposed to iodine-deficient diets
• Female predominance → 2–3 times more common in women

3. Aetiology and risk factors

• Iodine deficiency → most common cause worldwide
• Goitrogens → cabbage family vegetables, cassava, lithium, amiodarone
• Physiological → puberty, pregnancy
• Dyshormonogenesis → enzyme defects in hormone synthesis
• Autoimmune → Graves' disease, Hashimoto's thyroiditis
• Neoplasm → adenoma, carcinoma

4. Pathogenesis

1. Low iodine → low thyroid hormone
2. Raised thyroid-stimulating hormone (TSH)
3. Diffuse follicular hyperplasia → diffuse goitre
4. Cycles of hyperplasia and involution
5. Nodule formation → multinodular goitre
6. Some nodules become autonomous → toxic multinodular goitre

5. Classification

By morphology

• Diffuse
• Nodular → solitary nodule, multinodular

By function

• Non-toxic (euthyroid)
• Toxic → Graves' disease, toxic multinodular goitre, toxic adenoma
• Hypothyroid → Hashimoto's, severe iodine deficiency

By epidemiology

• Endemic
• Sporadic

WHO grading

1. Grade 0 → no palpable or visible goitre
2. Grade 1 → palpable but not visible with the neck in normal position
3. Grade 2 → visible with the neck in normal position

6. Special forms of goitre

A. Retrosternal (substernal) goitre

• Significant part of the gland extends through the thoracic inlet into the mediastinum
• Most arise from a cervical goitre growing downwards
• Types → anterior (most common), posterior (behind the great vessels, trachea), isolated mediastinal (own blood supply from the chest)
• Compression in a fixed bony inlet:
  • Dyspnoea, orthopnoea, stridor
  • Dysphagia
  • Superior vena cava obstruction → facial plethora
• Pemberton's sign → raising both arms causes facial congestion and distress
• Vocal cord palsy → rare; suggests malignancy
• CT (non-contrast) → extent, tracheal compression
• Treatment → thyroidectomy through a cervical incision in most; sternotomy if below the aortic arch or posterior

B. Lingual and ectopic thyroid

• Failed descent of the thyroid → base of tongue
• May be the only functioning thyroid tissue

C. Thyroiditis

• Hashimoto's thyroiditis (chronic lymphocytic) → most common cause of hypothyroidism in iodine-replete areas; anti-thyroid peroxidase (TPO) antibodies; firm rubbery goitre; risk of thyroid lymphoma
• De Quervain's (subacute granulomatous) → after viral infection; painful tender gland, fever, raised ESR, transient hyperthyroidism, low radioiodine uptake; treat with NSAIDs or steroids
• Riedel's thyroiditis → rare, woody hard fibrosis extending into the neck; IgG4-related; mimics carcinoma; steroids, tamoxifen, isthmusectomy for compression
• Acute suppurative thyroiditis → bacterial; children with pyriform sinus fistula; drainage, antibiotics
• Painless and postpartum thyroiditis

D. Others

• Goitre of puberty and pregnancy
• Dyshormonogenetic goitre
• Amiodarone-induced goitre

7. Clinical picture

Symptoms

• Neck swelling, cosmetic concern
• Pressure symptoms → dyspnoea, dysphagia, choking, hoarseness
• Symptoms of hyper- or hypothyroidism

Signs

• Moves up on swallowing → attached to the larynx by the pretracheal fascia
• Diffuse or nodular, consistency, tenderness
• Lower border palpable or not (retrosternal extension)
• Tracheal deviation
• Bruit → Graves' disease
• Cervical lymph nodes → malignancy

8. Diagnosis

Laboratory

• TSH, free T4, free T3
• Thyroid antibodies → anti-TPO, TSH receptor antibodies (TRAb)
• Calcitonin → suspected medullary carcinoma

Imaging

• Ultrasound → size, nodules, suspicious features (TI-RADS)
• FNA of suspicious nodules → Bethesda classification
• Radioisotope scan → hot or cold nodules in hyperthyroidism
• CT or MRI → retrosternal extension, tracheal compression
• Flow-volume loop, laryngoscopy → vocal cord function before surgery

9. Treatment

Conservative

• Iodine supplementation → prevention of endemic goitre (iodised salt)
• Observation → small, asymptomatic, benign goitre
• Levothyroxine (TSH suppression) → reduces size in about 30%; side effects on heart and bone
• Radioactive iodine (RAI) → reduces size up to 50% in 1 year; toxic goitre, unfit patients

Surgical

• Indications:
  1. Compression of trachea or oesophagus
  2. Retrosternal extension
  3. Suspicion or proof of malignancy
  4. Toxic goitre not controlled medically
  5. Cosmetic concern, patient choice
• Operations:
  • Total thyroidectomy → procedure of choice for multinodular goitre
  • Hemithyroidectomy (lobectomy) → one-sided disease
  • Subtotal thyroidectomy → abandoned; recurrence > 50%
• After total thyroidectomy → lifelong levothyroxine

10. Complications of thyroidectomy

• Haemorrhage → neck haematoma, airway compression; open the wound at the bedside
• Recurrent laryngeal nerve injury → hoarseness (unilateral), stridor (bilateral)
• External branch of superior laryngeal nerve → loss of high pitch
• Hypoparathyroidism → hypocalcaemia, tetany, Chvostek's and Trousseau's signs
• Thyroid storm → in uncontrolled hyperthyroidism
• Hypothyroidism
• Tracheomalacia → long-standing large goitre
• Wound infection, keloid