Drug-Induced Thyroiditis

• Several drugs have been reported to cause a drug-induced thyroiditis:
  • Amiodarone
  • Interferon-alfa
  • Interleukin-2
  • Lithium:
    • Lithium has been reported to cause a non destructive thyroiditis:
      • Similar to sporadic silent thyroiditis.
  • Minocycline
• The clinical course of the drug induced thyroiditis is similar to the other forms of destructive thyroiditis:

• Importantly:
  • Patients on the offending drugs may also develop:
    • Subacute, sporadic, or suppurative thyroiditis:
      • So these diagnoses need to be evaluated before ascribing the thyroiditis to a drug.
• The thyroid abnormalities usually resolve with discontinuation of the offending drug.
• Two drugs that deserve special mention are amiodarone and interferon-alfa:
  • Amiodarone:
    • An iodine-rich drug used in the treatment of cardiac arrhythmias:
      • Is well recognized to produce thyrotoxicosis by two forms:
        • Iodine-induced hyperthyroidism (type I)
        • Destructive thyroiditis (type II)
    • Distinguishing between the two forms is often a diagnostic dilemma:
      • And occasionally both forms may be present in the same patient.
    • In general:
      • Type II amiodarone-induced thyrotoxicosis occurs in:
        • A previously normal thyroid
        • The 24 RAIU is completely suppressed
        • Color flow Doppler ultrasonography shows absent vascularity.
    • The thyrotoxicosis usually responds to:
      • High doses of prednisone (40 to 60 mg daily):
        • Consistent with the underlying inflammatory process.
      • In all cases of amiodarone-induced thyrotoxicosis:
        • The drug should be discontinued if at all possible.
  • Interferon-alpha:
    • Is an immunomodulatory drug that is used in a variety of clinical conditions:
      • Most commonly in the treatment of viral hepatitis.
    • Up to 70% of patients without previous thyroid autoimmunity will develop:
      • High serum thyroid peroxidase antibody concentrations during interferon therapy.
    • Like amiodarone; two forms of interferon-induced thyrotoxicosis have been described:
      • A Graves’-like hyperthyroidism
      • A destructive thyroiditis
    • Frequently:
      • The thyrotoxicosis is mild and symptomatic therapy is often all that is necessary.
    • Because treatment with interferon-alpha is for a defined period:
      • The drug usually can be continued to finish the course of therapy when thyroid dysfunction develops.
      • Thyroid function usually normalizes after the interferon is stopped:
        • However, affected patients are at increased risk for autoimmune thyroid dysfunction in the future

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