What are the Wolff-Chaikoff effect and the Jod-Basedow effect?

Wolff-Chaikoff Effect and Jod-Basedow Effect: Thyroid Autoregulatory Mechanisms

The Wolff-Chaikoff effect is an autoregulatory mechanism where the thyroid gland temporarily inhibits thyroid hormone synthesis in response to excess iodine, while the Jod-Basedow effect is the opposite phenomenon where excess iodine exposure causes hyperthyroidism in susceptible individuals. 1, 2

Wolff-Chaikoff Effect

Mechanism

• Occurs when the thyroid is exposed to large amounts of iodine
• Involves acute inhibition of iodine organification within 48 hours of exposure 1, 3
• Proposed mechanism: formation of iodopeptides that temporarily inhibit thyroid peroxidase (TPO) mRNA and protein synthesis 1
• Serves as a protective mechanism to prevent excessive thyroid hormone production

Escape Phenomenon

• In normal individuals, the inhibitory effect is temporary (few days)
• "Escape" occurs through downregulation of the sodium iodine symporter (NIS)
• This reduces intrathyroidal iodine concentration, allowing normal TPO-H2O2 system activity to resume 1
• Results in normalization of T3 and T4 production

Failure to Escape

Certain individuals fail to escape from the Wolff-Chaikoff effect, resulting in hypothyroidism:

• Fetuses and newborns
• Elderly individuals
• Patients with autoimmune thyroiditis
• Patients previously treated for Graves' disease (with RAI, surgery, or antithyroid drugs)
• Patients with history of postpartum or subacute thyroiditis
• Some patients with chronic systemic diseases 1, 3

Jod-Basedow Effect

Mechanism

• Also known as iodine-induced hyperthyroidism (IIH)
• Occurs when excess iodine exposure leads to increased thyroid hormone production
• Results from absent thyroid autoregulation 2, 4

Risk Factors

• Historically seen in iodine-deficient populations suddenly exposed to iodine
• Modern cause: exposure to iodinated contrast media in radiological procedures
• Common in patients with pre-existing thyroid conditions, particularly:
  • Longstanding multinodular goiter
  • Latent Graves' disease
  • Autonomous nodular thyroid disease 2, 4

Clinical Presentation

• Thyrotoxicosis following iodine exposure
• Can lead to serious complications:
  • Arrhythmias
  • Heart failure
  • Pulmonary arterial hypertension
  • Cerebrovascular and pulmonary embolism
  • Cardiomyopathy 2

Clinical Implications

Iodine Sources Leading to These Effects

• Iodinated contrast media (most common modern cause)
• Amiodarone
• Iodine-containing supplements
• Iodine-rich or iodine-fortified foods 5

Management

• For Wolff-Chaikoff induced hypothyroidism:

  • Usually transient, resolving 2-3 weeks after iodine withdrawal
  • May require temporary thyroid hormone replacement in some cases 1, 3

• For Jod-Basedow induced hyperthyroidism:

  • Remove source of excess iodine
  • Treat thyrotoxicosis (beta-blockers, antithyroid drugs)
  • In severe cases, plasmapheresis may be required 2

Monitoring

• Patients who develop iodine-induced thyroid dysfunction should be monitored long-term
• Many patients with transient iodine-induced hypothyroidism may eventually develop permanent primary hypothyroidism 1
• Awareness of these phenomena is crucial when administering iodine-containing substances, especially to high-risk patients 2, 5

Prevention

• Screen for underlying thyroid disease before administering iodinated contrast when possible
• Consider alternative imaging techniques for high-risk patients
• Monitor thyroid function in susceptible individuals after iodine exposure 5