What is the management approach for a male teenager with low Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) levels?

Management of Low FSH and LH in a Male Teenager

A male teenager with low FSH and LH has secondary (hypogonadotropic) hypogonadism, requiring immediate measurement of serum prolactin and testosterone to determine the underlying cause and guide treatment—this is a critical diagnosis that can profoundly impact growth, sexual development, and future fertility. 1

Initial Diagnostic Workup

Essential Laboratory Tests

• Measure serum prolactin immediately in all patients with low testosterone combined with low or low-normal LH and FSH levels to screen for hyperprolactinemia 1
• Repeat prolactin measurement if initially elevated to ensure the elevation was not spurious 1
• Measure total testosterone to confirm hypogonadism and assess severity 1
• Check thyroid function (TSH, free T4) as thyroid disorders commonly disrupt the hypothalamic-pituitary-gonadal axis 2

Critical Imaging Decision

• Order pituitary MRI if testosterone is <150 ng/dL combined with low or low-normal LH, regardless of prolactin levels, as non-secreting adenomas may be present 1
• Refer to endocrinology immediately if prolactin remains persistently elevated, as this indicates possible prolactinoma or other pituitary pathology 1

Physical Examination Priorities

Key Findings to Document

• Testicular volume and consistency—small, soft testes suggest congenital hypogonadotropic hypogonadism 1
• Tanner staging to assess degree of pubertal development 1
• Body habitus and virilization status—examine body hair patterns in androgen-dependent areas 1
• Presence of gynecomastia which may indicate estrogen-testosterone imbalance 1
• Anosmia assessment as Kallmann syndrome (congenital hypogonadotropic hypogonadism with anosmia) is a common cause in adolescents 1

Differential Diagnosis Framework

Congenital/Developmental Causes

• Idiopathic hypogonadotropic hypogonadism (IHH) including Kallmann syndrome—most common congenital cause 1
• Genetic syndromes affecting GnRH secretion or action 1
• Pituitary developmental abnormalities 1

Acquired Causes in Teenagers

• Prolactinoma or other pituitary tumors 1
• Chronic illness including inflammatory conditions 1
• Eating disorders or excessive endurance exercise 1
• Medications that suppress gonadotropin secretion 1
• Obesity-related functional hypogonadism 3

Treatment Approach

If Fertility is NOT Currently a Concern

• Testosterone replacement therapy can be initiated after ruling out pituitary pathology 4
• Critical warning: Exogenous testosterone will suppress FSH and LH further through negative feedback, inhibiting spermatogenesis and potentially causing azoospermia 4, 2
• This suppression can take months to years to reverse after discontinuation 2

If Fertility Preservation is Important (Even Future Fertility)

• NEVER prescribe testosterone—it will completely suppress spermatogenesis through negative feedback on the hypothalamus and pituitary 2, 3
• Start with hCG injections to stimulate testosterone production and maintain testicular function 2
• Add FSH analogues after testosterone normalizes on hCG if needed to support spermatogenesis 2
• Treatment with hCG followed by FSH can successfully initiate spermatogenesis in 75% of men with hypogonadotropic hypogonadism 2

Special Considerations for Adolescents

• Timing is critical—delayed treatment can result in incomplete sexual development and compromised final adult height 1
• Bone age assessment may be warranted as androgens affect epiphyseal closure 4
• Psychological support is essential given the impact on body image and peer relationships during adolescence 1

Common Pitfalls to Avoid

Diagnostic Errors

• Do not assume "constitutional delay" without proper workup—true hypogonadotropic hypogonadism requires treatment 5
• Do not order a single hormone measurement—gonadotropins are pulsatile and require confirmation 2
• Do not skip prolactin measurement—this is a strong recommendation with Grade A evidence 1

Treatment Errors

• Never start testosterone in a teenager without ruling out pituitary pathology first 1
• Never prescribe testosterone if any future fertility is desired—use hCG/FSH instead 2, 3
• Do not delay endocrine referral if pituitary imaging shows abnormalities or prolactin remains elevated 1

Prognosis and Long-term Monitoring

Expected Outcomes with Treatment

• With hCG/FSH therapy: 75% achieve sperm in ejaculate, preserving fertility potential 2
• With testosterone alone: Sexual development proceeds normally but fertility is compromised 4
• Untreated: Permanent sexual infantilism, osteoporosis, and infertility 1

Monitoring Parameters

• Testosterone levels every 3-6 months during dose titration 1
• LH and FSH levels if using hCG/FSH therapy to assess response 2
• Semen analysis if fertility is a goal, once treatment is established 1, 2
• Bone density if treatment is delayed or inadequate 1