Pathophysiology: Primary vs Secondary Hypogonadism
Primary Hypogonadism (Testicular Failure — Hypergonadotropic)
- Caused by disease of the testes → decreased testosterone and sperm production
- Pituitary responds by increasing LH and FSH ("hypergonadotropic hypogonadism")
- Elevated LH/FSH indicate primary hypogonadism even if testosterone is in the low-normal range
- More likely to cause gynecomastia (high gonadotropins → increased aromatase activity) and decreased sperm production
Secondary Hypogonadism (Hypothalamic-Pituitary Dysfunction — Hypogonadotropic)
- Caused by disease or suppression of the hypothalamus or pituitary → decreased LH and FSH secretion
- Both testosterone and sperm production are reduced, but LH/FSH are normal or low ("hypogonadotropic hypogonadism")
- Reduced LH → decreased testicular testosterone → reduced intratesticular testosterone → impaired spermatogenesis
Summary
| Primary | Secondary | |
|---|---|---|
| Site of problem | Testes | Hypothalamus / Pituitary |
| Testosterone | Low | Low |
| LH / FSH | High | Normal or Low |
| Term | Hypergonadotropic | Hypogonadotropic |
| Gynecomastia | More common | Less common |
Source: UpToDate — Clinical features and diagnosis of male hypogonadism
Related notes: