Can local iodine treatment for a wound lead to hypothyroidism?

Topical Iodine Treatment and Risk of Hypothyroidism

Yes, local iodine treatment for wounds can lead to hypothyroidism, particularly with prolonged use or large wound areas, as iodine can be systemically absorbed and disrupt thyroid function.

Mechanism and Risk Factors

Topical iodine preparations (such as povidone-iodine/PVP-I) used for wound care can be absorbed through the skin, leading to excessive systemic iodine levels. This absorption is particularly significant when:

• Applied to large wound surfaces
• Used for prolonged periods
• Applied to burn wounds, fasciotomies, or in mediastinitis treatment
• Used in patients with pre-existing thyroid conditions

The absorbed iodine can induce hypothyroidism through the Wolff-Chaikoff effect, where excess iodine temporarily inhibits thyroid hormone synthesis 1. While most people "escape" from this effect after a few days, certain individuals fail to adapt and develop clinical or subclinical hypothyroidism.

High-Risk Populations

Patients at increased risk of developing iodine-induced hypothyroidism include:

• Those with pre-existing autoimmune thyroid disease (Hashimoto's thyroiditis)
• Patients with previous thyroid dysfunction
• Individuals who have undergone thyroid surgery or radioactive iodine treatment
• Patients with reduced kidney function
• Elderly patients

A study of long-term povidone-iodine treatment found that out of 27 patients, subclinical hypothyroidism developed in 3 patients (11%) 2.

Clinical Monitoring

For patients receiving topical iodine treatment on wounds:

1. Thyroid Function Monitoring:

   • Consider baseline thyroid function tests (TSH, FT4) before initiating treatment for large wounds
   • Monitor thyroid function periodically during prolonged treatment
   • Be vigilant for clinical signs of hypothyroidism (fatigue, cold intolerance, weight gain)

2. When to Suspect Iodine-Induced Hypothyroidism:

   • Unexplained fatigue or other hypothyroid symptoms during treatment
   • Elevated TSH with normal or low FT4
   • Symptoms appearing after weeks of topical iodine use

Management Recommendations

If hypothyroidism develops during topical iodine treatment:

1. For Mild/Subclinical Hypothyroidism:

   • Consider thyroid hormone replacement even with subclinical hypothyroidism if fatigue or other symptoms are present 3
   • Start levothyroxine at 0.5-1.5 μg/kg (lower doses for elderly or those with cardiac history)

2. For Moderate to Severe Cases:

   • Discontinue topical iodine if possible and switch to alternative antiseptics
   • Initiate thyroid hormone replacement therapy
   • Monitor for improvement after iodine withdrawal (function may return to normal in 2-3 weeks) 1

Prevention Strategies

To minimize risk of iodine-induced hypothyroidism:

• Limit duration of topical iodine use when possible
• Consider alternative antiseptics for patients with known thyroid disease
• Use the minimum effective concentration and amount of iodine-containing products
• Be particularly cautious with extensive wounds or burns where absorption is greater

Long-Term Considerations

Patients who develop iodine-induced hypothyroidism should be followed long-term, as many will eventually develop permanent primary hypothyroidism 1. Additionally, recent evidence suggests iodine-induced hypothyroidism may be associated with increased risk of heart failure (adjusted HR 1.11), with women at particularly higher risk (adjusted HR 1.65) 4.

Remember that while hypothyroidism is the most common thyroid dysfunction associated with topical iodine, hyperthyroidism can also occur in certain patients, particularly those with pre-existing nodular thyroid disease 3, 5.