Thyroiditis

Inflammation of the thyroid gland

Hashimoto's thyroiditis (chronic lymphocytic or autoimmune thyroiditis)

• • Chronic, progressive autoimmune disorder characterised by diffuse lymphocytic infiltration with formation of germinal centres, follicular cell atrophy, Hurthle cell metaplasia, Hurthle cell nodules, and fibrosis
  • Risk factors
    • Familial (RR of 9 with first-degree relatives)
    • Autoimmune conditions
    • Female (10:1 ratio)
  • Pathophysiology
    • Presence of circulating autoantibodies to thyroid antigens
    • Results in a chronic autoimmune destructive process involving the formation of immune complexes and complement in the basement membrane of follicular cells
    • Leads to infiltration of lymphocytes into the thyroid follicles and eventual fibrosis
    • Decreases the effective number of follicles available to produce thyroid hormones
    • Associated with an increased risk of papillary thyroid cancer
  • Presentation
    • Can be thyrotoxic or hypothyroid
    • Usual goitre symptoms
    • Nontender, diffusely firm, bumpy or bosselated thyroid gland
    • Rapidly enlarging goitre should raise concerns for thyroid lymphoma - needs FNA + flow cytometry
  • Workup
    • Antimicrosomal and antithyroglobulin antibody titres
      • TPOAb and TgAb
      • See 'thyroid physiology/biomarkers' for details
    • TSH +/- free T4/T3
    • USS neck not technically necessary, but can be done if neck pain or globus sensation
      • Coarse, heterogenous and hypoechoic parenchymal echotexture with increase vascularity, often with the presence of fine echogenic septae producing a pseudonodular appearance
      • Size can range from diffusely or focally enlarged to small and atrophic
      • May be enlarged lymph nodes around it
      • Any suspicious thyroid nodules or lymph nodes should be worked up with FNA
    • Diagnosis can also be made by FNA
  • Treatment
    • Thyroid replacement if hypothyroid, which results in a decrease in goitre size
    • Otherwise no treatment
  • Indications for thyroidectomy
    • Large goitre and compressive symptoms
    • Associated nodular disease if suspicion of cancer

Post-partum thyroiditis

• • Typically short-lived - resolution in 2-4 months
  • Short course of exogenous replacement may be necessary

Subacute granulomatous (de Quervain's) thyroiditis

• • Self-limited inflammation of thyroid occurring after a viral URTI and lasting 1-3 months
  • Acute onset pain, swelling, thyrotoxicosis, low-grade fevers, elevated ESR
  • Multi-nucleated giant cell granulomas, with granulomatous changes in the thyroid follicles
  • NSAIDs may be useful, or failing that, prednisolone 40mg daily
  • No surgical indications
  • Vast majority of patients return to a euthyroid state spontaneously

Painless or silent or postpartum thyroiditis (lymphocytic thyroiditis)

• • Autoimmune-mediated, self-limited disease
  • Thyrotoxic phase then euthyroid phase then hypothyroid then recovery
  • Recurrences common
  • Surgery not indicated

Drug-induced thyroiditis

• • Significant adverse effect
    • Interferon alpha
    • Amiodarone
      • Type I - pre-existing goitre - iodine-induced increase in thyroid hormone synthesis
        • Analogous to thyroiditis with normal/high RAI uptake - in this instance, there is excess thyroid hormone synthesis due to iodine load in amiodarone.
      • Type II - more common - no pre-existing thyroid disease - destruction of follicular cells resulting in increased release of stored thyroid hormones - can be very slow to resolve due to stored amiodarone in fat. Analogous to thyroiditis with destruction of gland and release of pre-formed thyroid hormone.
        • High-dose pred will be needed - often for a good 4-week course of high-dose (50mg daily)
        • Radioactive iodine is ineffective
        • Persistent amiodarone induced thyrotoxicosis despite medical therapy needs a total thyroidectomy

	Type 1	Type 2
Underlying thyroid disease	Yes (Multinodular goiter, Grave’s)	No
Time after starting amiodarone	Short (median 3 months)	Long (median 30 months)
24-hour iodine uptake	Low-Normal (may rarely be high in iodine deficient regions)	Low to Suppressed
Thyroid Ultrasound	Diffuse or Nodular Goiter may be present	Normal or small gland
Vascularity on Echo-color Doppler ultrasound	Increased	Absent
T4/T3 ratio	Usually <4	Usually >4
TgAb / TPOAb/ TSI	May be present	Usually absent
Circulating interleukin-6	Normal to high	Sometimes markedly elevated but usually doesn’t differentiate from AIT1

• Note
  • Amiodarone directly inhibits conversion of T4 to T3, so T3 is typically normal
  • Usually sestamibi study is necessary to exclude AIT1
  • Look for features of pre-existing disease e.g. thyroiditis on USS to differentiate between AIT1 and AIT2
  • Treat with prednisolone and carbimazole and cease amiodarone
  • If worsening thyrotoxicosis on good medical therapy, consider thyroidectomy (I have seen a three-week trial of medical therapy in practice)
  • Sestamibi can differentiate between AIT1 and AIT2 - there will be uptake present in AIT1, but not AIT2
  • Pertechnetate study is not useful because need to be off amiodarone for two months prior for it to be diagnostic

• Tyrosine kinase inhibitors

Radioiodine-induced thyroiditis

• • Transient, resolves within a week with simple analgaesia and anti-inflammatories

Riedel's thyroiditis

• • Extremely rare chronic idiopathic inflammatory disease - inflammation followed by fibrosis of thyroid and adjacent structures
  • Associations
    • 1/3 of patients have fibrosis elsewhere
    • PSC
    • Orbital pseudotumour
    • Autoimmune diseases including Addison's/diabetes
  • Presentation
    • Enlarging, tender goitre
    • Patients often suspected of having anaplastic carcinoma
    • Rock hard fixed neck mass
    • Often have clinically significant airway obstruction, dysphagia and dysphonia
  • Workup
    • TSH - generally high
    • Serum calcium
    • USS. FNA is often impossible due to hardness of mass!
    • CT CAP to look for fibrosis elsewhere and evaluate the rock-hard neck mass
    • Definitive diagnosis requires open biopsy - distinguished from thyroid cancer with immunohistochemistry
    • Isthmusectomy can relieve obstruction
  • Management
    • Often end up requiring surgery to exclude anaplastic cancer, or to treat obstructive symptoms
    • Surgery very challenging due to obliteration of planes and landmarks
    • Resect only the necessary segments to achieve the operative goal
  • Prognosis
    • May stabilise, resolve spontaneously, or progress over time
    • Treat with high-dose corticosteroids
    • Tamoxifen reduces goitre size
    • Will need levothyroxine
    • Rituximab may help
    • May need to treat hypoparathyroidism
    • No increased risk of thyroid cancer

Acute suppurative thyroiditis

• • Rare and potentially life-threatening infection
  • Pathophysiology
    • Often occurs in immunocompromised patients
    • Generally haematogenous spread
    • Possible underlying congenital pyriform sinus fistula
    • Most commonly Staph or strep
  • Presentation
    • Neck pain
    • Dysphagia
    • Odynophagia
    • Tender goitre (unilateral)
    • Sepsis
    • Usually euthyroid
  • Treatment
    • Abx - staph/strep most common
    • USS to confirm diagnosis with thyroid aspirate MCS
    • CT to assess for anatomical reason for infection ?fistula/abscess
    • Abscess drainage - try USS guided first, then open

Presentation

• Neck pain/tenderness
• Enlargement of thyroid
• Thyroid dysfunction
• Fever
• Can be euthyroid, thyrotoxic, or hypothyroid

Workup

• TSH, T3, T4
• Antimicrosomal Ab titre
• ESR/CRP - will be elevated in de Quervain's
• Thyroid scintigraphy
• USS
• CT - primarily to determine extent of substernal extension and mass effect