What are the common causes of elevated Thyroid-Stimulating Hormone (TSH) levels, specifically in Bihar?

Common Causes of TSH > 10 in Bihar: Prevalence Stratification

Iodine deficiency is the most common cause of elevated TSH levels (>10 mIU/L) in Bihar, followed by Hashimoto's thyroiditis (chronic autoimmune thyroiditis). 1

Prevalence-Based Stratification of Causes in Bihar

High Prevalence Causes

1. Iodine Deficiency - Most common worldwide environmental cause of hypothyroidism 2, 1

   • Bihar has historically been part of the "goiter belt" in India
   • Manifests as endemic goiter in regions with inadequate iodine fortification
   • Programs providing 150-200 μg/day iodine in deficient populations can temporarily increase TSH levels during correction phase 2

2. Hashimoto's Thyroiditis (Chronic Autoimmune Thyroiditis) 3, 1

   • Most common cause in iodine-sufficient areas
   • Characterized by thyroid antibodies (anti-TPO, anti-thyroglobulin)
   • Higher prevalence in women than men

Moderate Prevalence Causes

1. Post-Pregnancy Thyroiditis

   • Postpartum women should be screened due to risk of thyroid dysfunction 3
   • Can present as transient hypothyroidism with elevated TSH

2. Drug-Induced Hypothyroidism

   • Amiodarone (antiarrhythmic) 2, 1
   • Lithium (psychiatric medication)
   • Iodine-containing contrast agents 2

3. Subacute Thyroiditis (recovery phase)

   • Viral etiology, often following upper respiratory infection
   • Transient hypothyroidism following thyrotoxic phase

Low Prevalence Causes

1. Post-Radioactive Iodine Treatment

   • Following treatment for hyperthyroidism or thyroid cancer

2. Post-Thyroidectomy

   • Surgical removal of thyroid gland (partial or complete)

3. Congenital Hypothyroidism

   • Present from birth, requires newborn screening
   • Can lead to cretinism if untreated 2

4. Central Hypothyroidism (rare)

   • Pituitary or hypothalamic dysfunction
   • Usually presents with multiple hormone deficiencies

Clinical Implications of TSH > 10

• TSH > 10 mIU/L indicates overt hypothyroidism when accompanied by low free T4 3
• Treatment with levothyroxine is generally recommended when TSH exceeds 10 mIU/L 3
• Untreated hypothyroidism increases risk of:
  • Cardiovascular disease and increased mortality 3
  • In pregnancy: preeclampsia, preterm delivery, heart failure, and miscarriage 2, 3

Diagnostic Approach for Elevated TSH in Bihar

1. Confirm with thyroid function tests:

   • TSH > 10 mIU/L with low free T4 confirms overt hypothyroidism 3
   • TSH > 10 mIU/L with normal free T4 indicates severe subclinical hypothyroidism

2. Evaluate for autoimmune etiology:

   • Check anti-TPO and anti-thyroglobulin antibodies
   • Positive antibodies suggest Hashimoto's thyroiditis

3. Assess iodine status:

   • 24-hour urinary iodine excretion 2
   • Particularly important in regions with known iodine deficiency

4. Thyroid ultrasound:

   • Evaluate for nodules, goiter, or characteristic changes of thyroiditis
   • Annual neck ultrasound recommended for cancer surveillance 3

Management Considerations

• Oral levothyroxine monotherapy is standard treatment for hypothyroidism 3, 1
• Starting dose typically 1.6 μg/kg/day, titrated to achieve TSH 0.4-4.0 mIU/L 4
• In iodine-deficient areas, iodine supplementation (150 μg/day) is recommended 2
• Monitor thyroid function every 2-3 months initially, then every 6-12 months once stable 3

Special Considerations for Bihar

• Iodine supplementation programs must be carefully monitored as they can temporarily increase both subclinical hypothyroidism and hyperthyroidism during correction phase 2, 5
• Chronic exposure to excess iodine can induce autoimmune thyroiditis 2, 5
• In severe iodine deficiency, both T4 and T3 can be low, affecting fetal development during pregnancy 6

Remember that elevated TSH > 10 mIU/L requires treatment in most cases to prevent long-term complications, regardless of the underlying cause.