Does Severe Hyperthyroidism Raise FSH in Males?
No, severe hyperthyroidism does not typically raise FSH levels in males; in fact, FSH levels are usually normal or only modestly elevated, while testosterone and estradiol levels are significantly increased. 1, 2
Hormonal Changes in Male Hyperthyroidism
The primary hormonal alterations in hyperthyroid men involve:
- FSH levels remain normal in most cases of hyperthyroidism, with no significant difference compared to healthy controls 2
- LH secretion is increased in all hyperthyroid patients, reflecting enhanced pituitary responsiveness to GnRH 3
- Testosterone (T) and estradiol (E2) levels are significantly elevated (p < 0.005) in hyperthyroid men compared to controls 2
- Sex hormone-binding globulin (SHBG) is markedly increased, which paradoxically leads to a decreased Free Androgen Index despite elevated total testosterone 3
Mechanism of Gonadotropin Response
The hypothalamic-pituitary-gonadal axis shows specific adaptations in hyperthyroidism:
- Pituitary gonadotrophs become "hypersensitive" to GnRH during thyrotoxicosis, with significantly larger LH and FSH responses to exogenous GnRH stimulation compared to the euthyroid state 4
- FSH responsiveness to GnRH is enhanced (FSH incremental area: 825 ± 193 vs. 542 ± 98 in euthyroid state, p < 0.05), though basal FSH remains normal 4
- The pulsatile characteristics of LH and FSH secretion (frequency, peak shape) remain unchanged despite the hyperthyroid state 3
Clinical Implications
When evaluating a male patient with hyperthyroidism:
- Do not expect elevated FSH as a marker of hyperthyroidism - this is not a characteristic finding 2, 3
- Look for elevated testosterone and estradiol instead, which are the hallmark hormonal changes in male hyperthyroidism 1, 2
- Gynecomastia is common due to elevated estradiol levels 1
- These hormonal changes are reversible - FSH, LH, testosterone, and estradiol levels return to normal after successful treatment of hyperthyroidism 2
Important Distinction from Hypothyroidism
This contrasts sharply with primary hypothyroidism:
- Primary hypothyroidism in male children causes elevated FSH with testicular enlargement without virilization 1
- Adult men with primary hypothyroidism have reduced free testosterone and subnormal LH responses to GnRH 1