Can Follicle-Stimulating Hormone (FSH) be temporarily elevated in males due to thyroid dysfunction?

FSH Elevation in Males Due to Thyroid Dysfunction

Yes, FSH can be temporarily elevated in males due to thyroid dysfunction, particularly in hypothyroidism, and typically normalizes with thyroid hormone replacement therapy. 1, 2

Relationship Between Thyroid Dysfunction and FSH Levels

Hypothyroidism and FSH Elevation

• Primary hypothyroidism is associated with hypogonadotropic hypogonadism in adult men, but can paradoxically cause elevated FSH levels, especially in male children 1
• Men with untreated primary hypothyroidism often show abnormal gonadotropin secretion patterns, which can include elevated FSH levels 2
• The elevation in FSH is typically temporary and resolves with appropriate thyroid hormone replacement therapy 2, 3

Hyperthyroidism and FSH Elevation

• Hyperthyroidism can also cause increased FSH secretion, particularly in men 4
• LH secretion is increased in all hyperthyroid patients, while FSH secretion is specifically increased in hyperthyroid men 4

Pathophysiological Mechanisms

• Thyroid hormone deficiency affects the hypothalamic-pituitary-gonadal axis, altering normal gonadotropin secretion patterns 1
• In hypothyroidism, there appears to be an effect on gonadotropin secretion at the level of the hypothalamus-pituitary, either directly or through modulation of prolactin secretion 2
• Elevated prolactin levels, which can occur in severe primary hypothyroidism, may contribute to altered FSH levels 1, 2
• Thyroid hormones also affect sex hormone-binding globulin (SHBG) concentrations, which can indirectly influence the feedback mechanisms regulating FSH 1

Clinical Implications and Normalization

• FSH levels typically normalize with thyroid hormone replacement therapy 2, 3
• In one study, elevated gonadotropin levels (including FSH at 6.3 ± 2.0 IU/l) during the hypothyroid phase were restored to normal (FSH 2.7 ± 0.9 IU/l) with thyroxine substitution therapy 3
• The normalization of FSH levels correlates with improvement in testicular function and testosterone levels 2, 3
• Some improvement in sperm count and motility is also observed after thyroid hormone replacement normalizes FSH levels 3

Clinical Evaluation and Management

• When elevated FSH is detected in males, thyroid function tests (TSH, free T4) should be considered as part of the diagnostic workup 1, 5
• TSH is the most sensitive test for monitoring thyroid function with a sensitivity above 98% and specificity greater than 92% 6
• If thyroid dysfunction is identified, appropriate treatment should be initiated to normalize thyroid function 2, 3
• For primary hypothyroidism, levothyroxine therapy is the standard treatment, which will typically resolve the associated FSH abnormalities 2

Important Considerations

• FSH elevation due to thyroid dysfunction should be distinguished from primary testicular failure, which also presents with elevated FSH 7
• In non-obstructive azoospermia, FSH levels greater than 7.6 IU/L strongly suggest primary testicular dysfunction rather than thyroid-related causes 7
• Radioactive iodine therapy (RAI) used to treat thyroid cancer can produce a dose-dependent impairment of spermatogenesis and elevation of FSH for up to approximately 2 years, which is a direct effect on the testes rather than through thyroid dysfunction 1

Understanding the relationship between thyroid dysfunction and FSH levels is important for proper diagnosis and management of male reproductive health issues, as addressing the underlying thyroid disorder can resolve hormonal abnormalities and improve reproductive function.