What is secondary hypogonadism?
A secondary hypogonadism is a form of hypogonadism in which the cause lies not in the testicles themselves, but in the hormonal control centers of the brain. The hypothalamus or the pituitary gland are affected, which normally produce the hormones that stimulate testosterone production in the testicles.
If these regulatory hormones are not released in sufficient quantities, the testicles receive too few signals to produce testosterone. As a result, testosterone levels drop, even though the testicles may fundamentally be functional.
Secondary hypogonadism is a common cause of testosterone deficiency and can be temporary or permanent.
How does secondary hypogonadism develop?
In secondary hypogonadism, the hormonal feedback loop between the brain and the testicles is disrupted. Normally, the hypothalamus produces the hormone GnRH, which stimulates the pituitary gland to release LH (luteinizing hormone) and FSH (follicle-stimulating hormone).
These two hormones then stimulate the testicles to produce testosterone and sperm.
If this feedback loop is disrupted, too little LH and FSH are produced. As a result, the testicles produce less testosterone, even though they may fundamentally be intact.
What causes can secondary hypogonadism have?
Secondary hypogonadism can be caused by various diseases or external factors.
The most common causes include:
- Diseases of the pituitary gland
- Diseases of the hypothalamus
- Pituitary tumors
- elevated prolactin (hyperprolactinemia)
- Traumatic brain injuries
- chronic diseases
- severe obesity
- sleep deprivation
- chronic stress
- certain medications, such as opioids or glucocorticoids
Severe obesity or other metabolic disorders can also affect the hormonal feedback loop and contribute to functional secondary hypogonadism.
What symptoms occur in secondary hypogonadism?
The symptoms are often similar to those of testosterone deficiency and usually develop gradually.
Typical symptoms include:
- decreased libido
- erectile dysfunction
- fatigue and exhaustion
- decreased muscle mass
- increased body fat
- reduced physical performance
- concentration difficulties
- depressive mood
- reduced beard growth
- fertility problems
Depending on the cause, additional symptoms may occur that indicate a disease of the pituitary gland or hypothalamus.
How is secondary hypogonadism diagnosed?
The diagnosis is based on the symptoms as well as targeted hormone testing.
Typically, the following laboratory findings are observed:
- Total testosterone is low
- Free testosterone is low
- LH is low or at the lower end of the normal range
- FSH is low or at the lower end of the normal range
Depending on the question, other laboratory values are often determined, including:
- SHBG
- Estradiol
- Prolactin
If a disease of the pituitary gland or hypothalamus is suspected, a magnetic resonance imaging (MRI) scan of the head may also be required.
How does secondary hypogonadism differ from primary hypogonadism?
The crucial difference lies in the location of the disruption.
In secondary hypogonadism, the cause lies in the hypothalamus or the pituitary gland. These produce too little LH and FSH, which means the testicles are not sufficiently stimulated.
In primary hypogonadism, on the other hand, the cause is directly in the testicles. Testosterone production is impaired there, even though sufficient LH and FSH are present. Typically, these hormones are even elevated in primary hypogonadism.
The determination of LH and FSH is therefore an important part of the diagnosis.
How is secondary hypogonadism treated?
Treatment is based on the underlying cause.
If a triggering disease or modifiable factor can be treated, hormone production may improve again in some cases.
If there is a persistently low testosterone level with corresponding symptoms and there are no contraindications, testosterone replacement therapy (TRT) may be considered.
If there is a current desire to conceive, alternative treatment strategies are often chosen to preserve or specifically stimulate the body's own testosterone and sperm production as much as possible.
Conclusion
Secondary hypogonadism is a form of testosterone deficiency in which the cause lies in the hypothalamus or the pituitary gland. Typically, testosterone levels are low, while LH and FSH levels are low or inappropriately normal.
Careful hormone testing helps to narrow down the cause and initiate the appropriate treatment. Our article Testosterone Deficiency in Men: Causes, Symptoms, and Solutions provides an overview of the signs and treatment.