Does iatrogenic hyperthyroidism in men increase Follicle-Stimulating Hormone (FSH) levels?

Effect of Iatrogenic Hyperthyroidism on FSH Levels in Men

Iatrogenic hyperthyroidism in men does not increase Follicle-Stimulating Hormone (FSH) levels; rather, it tends to maintain normal or slightly decreased FSH levels while elevating testosterone and estradiol. 1

Pathophysiology of Thyroid-Gonadal Axis in Hyperthyroidism

• Hyperthyroidism affects the hypothalamic-pituitary-gonadal axis in men, but unlike hypothyroidism (which causes hypogonadotropic hypogonadism), hyperthyroidism has different effects on reproductive hormones 2
• In men with hyperthyroidism, FSH and LH levels typically remain within normal range, not showing significant elevation compared to healthy controls 1
• The primary hormonal changes observed in male hyperthyroidism include:
  • Elevated serum testosterone levels 2, 1
  • Increased sex hormone-binding globulin (SHBG) concentrations 2
  • Elevated estradiol levels, which may contribute to gynecomastia in these patients 2

Clinical Manifestations and Laboratory Findings

• Men with hyperthyroidism exhibit hyperresponsiveness of LH to GnRH administration but show subnormal responses to human chorionic gonadotropin (hCG) 2
• The increased testosterone and estradiol levels in hyperthyroid men are considered adaptive responses to the high metabolic environment rather than primary gonadal dysfunction 1
• These hormonal alterations represent changes in the hypothalamus-pituitary-gonadal axis functioning during the hyperthyroid state 1

Treatment Effects on Hormone Levels

• When hyperthyroidism is successfully treated and controlled, all reproductive hormone levels (including testosterone and estradiol) return to normal ranges 1
• After treatment of hyperthyroidism, there is no significant difference in FSH, LH, testosterone, and estradiol levels between formerly hyperthyroid patients and healthy controls 1

Special Considerations for Iatrogenic Hyperthyroidism

• Iatrogenic hyperthyroidism (caused by excessive thyroid hormone replacement or other medications) follows the same pattern as endogenous hyperthyroidism regarding FSH levels 2
• Thyroid hormone therapy in normal men may elevate testosterone and SHBG similar to what is observed in hyperthyroidism 2
• For symptomatic iatrogenic hyperthyroidism, guidelines suggest interrupting the causative therapy and starting beta-blocker therapy to manage symptoms 3

Clinical Implications

• When evaluating male patients with iatrogenic hyperthyroidism, clinicians should not expect elevated FSH levels as part of the hormonal profile 1
• Monitoring of reproductive hormones in men with hyperthyroidism should focus on testosterone, estradiol, and SHBG rather than gonadotropins 2
• The European Society of Cardiology acknowledges the complex bidirectional relationship between thyroid hormones and reproductive hormones, which should be considered in clinical evaluation 3

Radioactive Iodine Therapy Considerations

• Radioactive iodine therapy (RAI) used for treating thyroid cancer or hyperthyroidism represents a special case that can affect FSH levels differently 2
• RAI can cause dose-dependent impairment of spermatogenesis and elevation of FSH for up to approximately 2 years 2
• This effect is distinct from the hormonal changes seen in untreated hyperthyroidism and represents direct testicular damage rather than thyroid hormone effects 2