thyroiditis

see also:

• thyroid physiology and hormones
• hyperthyroidism
• Mx of a low TSH
• thyroid storm
• Graves disease
• thyroid cancer

• thyroiditis is an inflammatory condition of the thyroid
• inflammation resolves in 95% within 12-18 months although may result in permanent hypothyroidism
  • most patients with Hashimotos' thyroiditis, radiation
  • 20% of painless or post-partum thyroiditis
  • 5% of subacute
• drug-induced normally resolves on cessation of the drug
• may increase risk of thyroid cancer

• 4-5 cases per 100,000 people
• women 4x as frequent as men
• usually 40-50yrs age
• summer peak
• usually associated with viral infections eg. coxsackievirus groups A and B and echovirus infections
• rarely may occur after vaccinations - see the unwell patient after Covid-19 vaccination
• prodrome of myalgias, pharyngitis, low-grade fever, and fatigue, followed by a tender, diffuse goiter and neck pain that often radiates up to the ear
• ESR, CRP are usually both raised, ESR usually > 50
• there may be mild anaemia and leukocytosis
• levels of antithyroid peroxidase and antithyroglobulin antibodies generally are normal
• 50% develop hyperthyroidism with elevated T4 and suppressed TSH for 3- 6 weeks until thyroid stores are depleted
• Most patients return to euthyroidism within 6-12 months
• 10-15% develop permanent hypothyroidism preceded by a transition phase of low TSH and T4 levels
  • the incidence of this is not reduced by steroid Rx
• may recur in 2%
• Dx:
  • send bloods for:
    • ESR
    • antibodies to peroxidase, thyrogulin and TSH receptor
  • radioactive iodine uptake (RAIU) at 24hrs < 5% (usually not needed)
  • high titre persistent anti-TPO antibodies
• DDx:
  • Graves disease but this has exophthalmos, pretibial myxoedema, thyroid thrill due to hypervascularity which may be evident on US, and RAIU at 24hrs is high, and CRP and ESR will usually be normal
• Rx:
  • non-steroidal anti-inflammatory drugs (NSAIDs)
  • antithyroid drugs are not effective during the thyrotoxic stage and have no place in treatment
  • if symptoms of hyperthyroidism, Rx with beta adrenergic blockers until this phase resolves
    • eg. propranolol 20mg bd for young adults (consider initial 10mg bd in older adults)
  • if no improvement within 1 week of NSAIDs, consider prednisolone 40-50mg/d and tapered to reduce over 2-6 weeks
    • eg. 50mg/d 1st week, 37.5mg/day 2nd week, 25mg/d 3rd week, 12.5mg/d 4th week
      • some may start at the 37.5mg/d dosing if symptoms are not too severe
  • repeat thyroid function tests in 3-4 weeks and warn of possibility of developing hypothyroidism and needing thyroxine supplementation.

• 10-15 cases per 100,000 people
• auto-immune disease associated with anti-thyroid antibodies
• similar clinically and pathologically to post-partum thyroiditis but occurs without post-partum status
• Dx:
  • RAIU at 24hrs < 5%
  • present and persistent anti-TPO antibodies

• auto-immune disease associated with anti-thyroid antibodies
• 5-7% of post-partum women
• most present with a painless, small, nontender, firm goiter within two to six months after delivery
• Dx:
  • RAIU at 24hrs < 5%
  • low or absent anti-TPO antibodies
• DDx:
  • Graves disease but this has exophthalmos, pretibial myxoedema, thyroid thrill due to hypervascularity which may be evident on US, and RAIU at 24hrs is high

• auto-immune disease associated with anti-thyroid antibodies
• 5-10% of cases of thyroiditis
• women are 7x more affected than men
• peak age 40-60yrs
• 90% have a symmetric diffuse goitre with a firm pebbly texture and is usually painless
• 10% have thyroid atrophy
• rates appear to be higher in areas proximate to active volcanoes such as near Mt Etna in Sicily where prevalance has increased 10 fold and males are much more represented ¹⁾
• Dx:
  • RAIU at 24hrs normal or low or high
  • 90-95% have high titre persistent anti-TPO antibodies
  • 20-30% have antithyroglobulin antibodies

• amiodarone
• lithium
• interferons
• cytokines
• Dx:
  • RAIU at 24hrs low
  • usually absent anti-TPO antibodies but may be present in a minority (a third of those with lithium thyroiditis)

• radioactive iodine Rx for hyperthyroidism
  • occurs in 1% of those being treated in this way for Graves disease
• external beam radiation Rx for certain cancers

• very rare
• unilateral thyroid gland tenderness with overlying erythema
• usually have high ESR, CRP and WCC with left shift
• various pathogens:
  • Streptococcus pyrogenes, Streptococcus aureus, or Streptococcus pneumoniae
  • fungal
  • mycobacterial
  • parasitic infections
• Dx:
  • RAIU at 24hrs normal
  • absent anti-TPO antibodies

• a rare chronic condition characterized by an extensive fibrotic process of unknown etiology involving the thyroid and adjacent structures
• women 4x frequency of men
• usually 30-60yr olds
• present with a rock-hard, wood-like, fixed, painless goiter, often accompanied by symptoms of oesophageal or tracheal compression and may present with stridor, dyspnea, a suffocating feeling, dysphagia, and hoarseness.
• 1/3rd have hypothyroidism
• 2/3rds have antithyroid peroxidase antibodies present
• RAIU typically is low

• most are painless and silent
• some have associated sore throat / painful thyroid gland:
  • subacute thyroiditis
  • radiation
  • trauma
  • bacterial thyroiditis
• rapidly progressive inflammation it may result in clinical hyperthyroidism for 1-3 months associated with throat pain, while those with a more gradual inflammation such as painless, post-partum and Hashimoto's thyroiditis may just develop hypothyroidism

• derived from https://www.aafp.org/afp/2006/0515/p1769.html

• if Hx of radiation or trauma then this is likely cause
• if no Hx of radiation or trauma
  • if not acute onset then likely to be subacute granulomatous
  • if acute onset then:
    • low RAIU at 24hrs:
      • then likely to be subacute granulomatous
    • normal RAIU at 24hrs:
      • possible suppurative thyroiditis

• is the patient on medications that can cause thyroiditis?
  • most likely drug-induced ⇒ cease medications
• if no medications:
  • if patient is not post-partum:
    • likely to be Hashimoto's or painless subacute lymphocytic
  • is the patient post-partum?
    • normal or high TSH:
      • likely to be Hashimoto's or post-partum thyroiditis
    • low TSH:
      • low RAIU at 24hrs ⇒ post-partum thyroiditis
      • high RAIU at 24hrs ⇒ Graves disease