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(See also Endocrine Disorders in Children: Male Hypogonadism in Children.)
Hypogonadism is defined as testosterone deficiency with associated symptoms or signs, deficiency of spermatozoa production, or both. It may result from a disorder of the testes (primary hypogonadism) or of the hypothalamic-pituitary axis (secondary hypogonadism). Both may be congenital or acquired as the result of aging, disease, drugs, or other factors. Additionally, a number of congenital enzyme deficiencies cause varying degrees of target organ androgen resistance. Diagnosis is confirmed by hormone levels. Treatment varies with etiology but typically includes gonadotropin-releasing hormone, gonadotropin, or testosterone replacement.
Etiology
Primary hypogonadism involves failure of the testes to respond to follicle-stimulating hormone (FSH) and luteinizing hormone (LH). When primary hypogonadism affects testosterone production, testosterone is insufficient to inhibit production of FSH and LH; hence, FSH and LH levels are elevated. The most common cause of primary hypogonadism is Klinefelter syndrome. It involves seminiferous tubule dysgenesis and a 47,XXY karyotype (see Chromosomal Anomalies: Klinefelter Syndrome (47,XXY)).
Secondary hypogonadism is failure of the hypothalamus to produce gonadotropin-releasing hormone (GnRH) or of the pituitary gland to produce enough FSH and LH. In secondary hypogonadism, testosterone levels are low and levels of FSH and LH are low or inappropriately normal. Any acute systemic illness can cause temporary secondary hypogonadism. Some syndromes of hypogonadism have both primary and secondary causes (mixed hypogonadism). Table 1: Male Reproductive Endocrinology and Related Disorders: Causes of Hypogonadism* lists some common causes of hypogonadism by category.
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Table 1
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| Causes of Hypogonadism* |
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Type
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Congenital Causes
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Acquired Causes
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Primary (testicular)
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Klinefelter syndrome
Anorchia (bilateral)
Cryptorchidism
Myotonic dystrophy
Enzymatic defects in testosterone synthesis
Leydig cell aplasia
Noonan syndrome
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Chemotherapy or radiation therapy
Testicular infection (eg, mumps, echovirus, flavivirus)
High doses of antiandrogen drugs (eg, cimetidine, spironolactone, ketoconazole, flutamide, cyproterone)
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Secondary (hypothalamic-pituitary)
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Idiopathic hypogonadotropic hypogonadism
Kallmann syndrome
Prader-Willi syndrome
Dandy-Walker malformation
Isolated luteinizing hormone deficiency
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Any acute systemic illness
Hypopituitarism (tumor, infarction, infiltrative disease, infection, trauma, irradiation)
Hyperprolactinemia
Iron overload (hemochromatosis)
Certain drugs (eg, estrogens, psychoactive drugs, metoclopramide, opioids, leuprolide, goserelin, triptorelin, newer androgen biosynthesis inhibitors for prostate cancer)
Cushing syndrome
Cirrhosis
Morbid obesity
Idiopathic
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Mixed
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—
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Aging
Alcoholism
Systemic disease (eg, uremia, liver failure, AIDS, sickle cell disease)
Drugs (ethanol, corticosteroids)
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*In approximate order of frequency.
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Some syndromes of hypogonadism (eg, cryptorchidism, some systemic disorders) affect spermatozoon production more than testosterone levels.
Symptoms and Signs
Age at onset of testosterone deficiency dictates the clinical presentation: congenital, childhood-onset, or adult-onset hypogonadism. Congenital hypogonadism may be of 1st-, 2nd-, or 3rd-trimester onset.
Congenital hypogonadism of 1st-trimester onset results in inadequate male sexual differentiation. Complete absence of testosterone's effects results in normal-appearing female external genitals. Partial testosterone deficiency results in abnormalities ranging from ambiguous external genitals to hypospadias. Second- or 3rd-trimester onset of testosterone deficiency results in microphallus and undescended testes.
Childhood-onset testosterone deficiency (see Endocrine Disorders in Children: Male Hypogonadism in Children) has few consequences and usually is unrecognized until puberty is delayed. Untreated hypogonadism impairs development of secondary sexual characteristics. As adults, affected patients have poor muscle development, a high-pitched voice, a small scrotum, decreased phallic and testicular growth, sparse pubic and axillary hair, and an absence of body hair. They may develop gynecomastia and eunuchoidal body proportions (span > height by 5 cm and pubic to floor length > crown to pubic length by > 5 cm) because of delayed fusion of the epiphyses and continued long bone growth.
Adult-onset testosterone deficiency has varied manifestations depending on the degree and duration of the deficiency. Decreased libido; erectile dysfunction; decline in cognitive skills, such as visual-spatial interpretation; sleep disturbances; vasomotor instability (in acute, severe male hypogonadism); and mood changes, such as depression and anger, are common. Decreased lean body mass, increased visceral fat, testicular atrophy, osteopenia, gynecomastia, and sparse body hair typically take months to years to develop. Testosterone deficiency may increase the risk of coronary artery disease.
Diagnosis
Congenital and childhood-onset hypogonadism are often suspected because of developmental abnormalities or delayed puberty. Adult-onset hypogonadism should be suspected on the basis of symptoms or signs but is easily missed because these clinical markers are insensitive and nonspecific. Klinefelter syndrome should be considered in adolescent males in whom puberty is delayed, young men with hypogonadism, and all adult men with very small testes. Hypogonadism requires confirmatory testing (see Fig. 2: Male Reproductive Endocrinology and Related Disorders: Laboratory evaluation of male hypogonadism. ).
Diagnosis of primary and secondary hypogonadism:
Increases in FSH and LH are more sensitive for primary hypogonadism than are decreases in testosterone levels. Levels of FSH and LH also help determine whether hypogonadism is primary or secondary. High gonadotropin levels, even with low-normal testosterone levels, indicate primary hypogonadism, whereas gonadotropin levels that are low or lower than expected for the level of testosterone indicate secondary hypogonadism. Alternatively, in boys of short stature with delayed puberty, low testosterone plus low gonadotropin levels might result from constitutional delay of puberty. Elevation of serum FSH with normal levels of serum testosterone and LH often occurs when spermatogenesis is impaired but testosterone production is normal. The cause of hypogonadism is often evident clinically. Primary hypogonadism requires no further testing, although some clinicians do a karyotype to definitively diagnose Klinefelter syndrome.
Total (and, when possible, free) serum testosterone, serum FSH, and serum LH levels are measured simultaneously. The normal range for total testosterone is 300 to 1000 ng/dL (10.5 to 35 nmol/L). The testosterone level should be drawn in the morning (before 10:00 am) to confirm hypogonadism. Because of the increase in sex hormone–binding globulin (SHBG) with aging, total testosterone level is a less sensitive indicator of hypogonadism after age 50. Although serum free testosterone more accurately reflects functional testosterone levels, its measurement requires equilibrium dialysis, which is technically difficult and not widely available. Some commercially available kits, including the analog free testosterone assay, attempt to measure serum free testosterone levels, but the results are often inaccurate, particularly in conditions, such as type 2 diabetes, obesity, and hypothyroidism, that alter SHBG levels. Free testosterone levels can be calculated based on SHBG, albumin, and testosterone values; there are calculators available online. See the Free and Bioavailable Testosterone Calculator. Because of the pulsatile secretion of FSH and LH, these hormones are sometimes measured as a pooled sample of 3 venipunctures taken at 20-min intervals, but these pooled samples seldom add clinically important information compared with a single blood sample. Serum FSH and LH levels are usually ≤ 5 mIU/mL before puberty and between 5 and 15 mIU/mL in adulthood.
Semen analysis should be done in all men who are seeking fertility treatment. In adolescents or adults, a semen sample collected by masturbation after 2 days of abstinence from ejaculation provides an excellent index of seminiferous tubular function. A normal semen sample has a volume of > 2.5 mL with > 20 million sperm/mL, of which 60% are of normal morphology and are motile (see also Infertility: Sperm Disorders).
Evaluation of secondary hypogonadism:
Because any systemic illness can temporarily decrease levels of testosterone, FSH, and LH, secondary hypogonadism should be confirmed by measuring these levels again at least 4 wk after resolution of the systemic illness. To confirm secondary hypogonadism in adolescents, the GnRH stimulation test may be considered. If, in response to IV GnRH, levels of FSH and LH increase, puberty is simply delayed. If levels do not increase, true hypogonadism is likely.
To help determine the cause of confirmed secondary hypogonadism, testing should include serum prolactin level (to screen for pituitary adenoma) and transferrin saturation (to screen for hemochromatosis—see Iron Overload: Hereditary Hemochromatosis). Sella imaging with MRI or CT is done to exclude a pituitary macroadenoma or other mass in men with any of the following:
Also, if there are symptoms or signs of Cushing syndrome, 24-h urine collection for free cortisol or a dexamethasone suppression test is done (see Adrenal Disorders: Cushing Syndrome). If no abnormalities are identified, the diagnosis is acquired idiopathic secondary hypogonadism.
Treatment
Treatment is directed toward providing adequate androgen replacement conveniently and safely. Although patients with primary hypogonadism will not become fertile with any endocrine therapy, patients with secondary hypogonadism often become fertile with gonadotropin therapy. Testosterone formulations discussed here are those available in the US. Other formulations may be available in other countries.
Testosterone replacement therapy (TRT):
Because exogenous testosterone impairs spermatogenesis, TRT should be avoided, when possible, in secondary hypogonadism or when subsequent fertility is a concern (unless there is irreversible primary testicular failure). Treatment of secondary hypogonadism in boys with gonadotropin replacement therapy (see Male Reproductive Endocrinology and Related Disorders: Treatment of infertility due to hypogonadism) usually stimulates androgen production as well as spermatogenesis.
TRT can be used for males who have no signs of puberty, are near age 15, and in whom secondary hypogonadism has been excluded. They may be given long-acting testosterone enanthate 50 mg IM once/mo for 4 to 8 mo. These low doses cause some virilization without restricting adult height. Older adolescents with testosterone deficiency receive long-acting testosterone enanthate or testosterone cypionate at a dose that is increased gradually over 18 to 24 mo from 50 to 100 to 200 mg IM q 1 to 2 wk. Transcutaneous gel may also be used, although it is more expensive, could possibly be transferred to others during intimate contact, and is more difficult to accurately dose. It is reasonable to convert older adolescents to testosterone gel 1% at adult dosages when their IM dosage has reached the equivalent of 100 to 200 mg q 2 wk.
Adults with established testosterone deficiency may benefit from replacement therapy. Treatment slows the course of osteopenia, muscle loss, vasomotor instability, loss of libido, depression, and occasionally erectile dysfunction. Although the effects of testosterone on coronary artery disease are not completely understood, testosterone replacement therapy may improve coronary artery blood flow and may decrease the risk of coronary artery disease. Options for replacement therapy include testosterone gel 1% or 1.62% (5 to 10 g daily to deliver 5 to 10 mg daily), IM testosterone enanthate or cypionate (100 mg q 7 days or 200 mg q 10 to 14 days), a buccal mucosal lozenge (30 mg bid), or a transdermal testosterone patch (5 to 10 mg daily). Testosterone gel maintains physiologic blood levels more consistently than other treatments, but IM or patch systems are sometimes preferred because of their lower cost.
Potential adverse effects of testosterone and its analogs include erythrocytosis (particularly in men > 50 yr receiving IM testosterone), acne, gynecomastia, low sperm count, and very rarely prostatic enlargement or edema; prostatic obstructive symptoms are rare. Currently, replacing testosterone enough to achieve physiologic levels is not thought to cause new prostate cancer or accelerate growth or spread of localized prostate cancer. TRT is contraindicated in men with prostate cancer, and men who have or are at high risk of prostate cancer should be counseled and carefully followed with digital rectal examinations and serum prostate-specific antigen (PSA) measurements while taking TRT. A prostate biopsy may be needed if PSA elevation is sustained after TRT is stopped. Injectable or transdermal forms of testosterone are preferable. Oral formulations are unpredictably absorbed and carry risks of hepatocellular dysfunction and hepatic adenoma.
Men taking supplemental testosterone should be monitored periodically. Hct should be checked every 6 to 12 mo. Digital rectal examination and PSA testing should be offered every 6 mo. If Hct is ≥ 54%, the testosterone dose should be reduced. Because the effect of testosterone replacement on PSA levels is not clear, significant increases in PSA level should prompt consideration of prostate biopsy in men who would otherwise be candidates for prostate cancer diagnosis and treatment.
Treatment of infertility due to hypogonadism:
Infertility, which has many possible causes other than hypogonadism, is discussed in full elsewhere (see Infertility). Infertility due to primary hypogonadism does not respond to hormonal therapy. Men with primary hypogonadism occasionally have a few intratesticular sperm that can be harvested with various microsurgical techniques and used to fertilize an egg by assisted reproductive technique (eg, intracytoplasmic injection).
Infertility due to secondary hypogonadism usually responds to gonadotropin replacement therapy. Other symptoms of secondary hypogonadism respond well to testosterone replacement therapy alone. If secondary hypogonadism results from pituitary disease, gonadotropin replacement therapy usually is successful. Therapy begins with replacement of LH and FSH. LH replacement is initiated using human chorionic gonadotropin (hCG) at doses of 1500 IU sc 3 times/wk. FSH replacement, which is expensive, uses human menotropic gonadotropin or human recombinant FSH, at doses of 150 IU 3 times/wk. Doses may be adjusted based on the results of periodic testing with semen analysis and levels of serum FSH, LH, and testosterone. Once an adequate sperm count is achieved, FSH can be stopped. Most men who have secondary hypogonadism due to a hypothalamic defect (eg, idiopathic hypogonadotropic hypogonadism, Kallmann syndrome) become fertile with treatment despite sperm counts that are low (eg, < 5 million/mL). When LH and FSH treatment is ineffective, pulsatile GnRH replacement therapy (q 2 h sc by a programmable minipump), although less readily available, might be more effective. Most (80 to 90%) of men respond successfully to these regimens.
Key Points
Last full review/revision February 2013 by Irvin H. Hirsch, MD
Content last modified March 2013
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