Endocrine disorders can result from
Dysfunction originating in the peripheral endocrine gland itself (primary disorders)
Understimulation by the pituitary (secondary disorders) whether due to intrinsic pituitary dysfunction or understimulation of the pituitary by the hypothalamus
Overstimulation by the pituitary (secondary disorders) whether due to intrinsic pituitary dysfunction or overstimulation of the pituitary by the hypothalamus
Rarely, because of abnormal tissue response to hormones (usually hypofunction).
The disorders can result in hormone overproduction (hyperfunction) or underproduction (hypofunction).
(See also Overview of the Endocrine System.)
Endocrine hyperfunction
Hyperfunction of endocrine glands may result from overstimulation by the pituitary whether due to intrinsic pituitary dysfunction or overstimulation of the pituitary by the hypothalamus. However, hyperfunction of endocrine glands is most commonly due to hyperplasia or neoplasia of the gland itself. In some cases, cancers from other tissues can produce hormones (ectopic hormone production).
Hormone excess also can result from exogenous hormone administration. In some cases, patients take nonprescription products that contain hormones and may not know or tell the physician.
Tissue hypersensitivity to hormones can occur. Antibodies can stimulate peripheral endocrine glands, as occurs in hyperthyroidism of Graves disease. Disruption of a peripheral endocrine gland can rapidly release stored hormone (eg, thyroid hormone release in subacute thyroiditis).
Enzyme defects in the synthesis of a peripheral endocrine hormone can result in overproduction of hormones proximal to the block. Finally, overproduction of a hormone can occur as an appropriate response to a disease state.
Endocrine hypofunction
Hypofunction of an endocrine gland can result from understimulation by the pituitary whether due to intrinsic pituitary dysfunction or understimulation of the pituitary by the hypothalamus.
Hypofunction originating within the peripheral gland itself can result from congenital or acquired disorders (including autoimmune disorders, tumors, infections, vascular disorders, and toxins).
Genetic disorders causing hypofunction can result from deletion of a gene or by production of an abnormal hormone. A decrease in hormone production by the peripheral endocrine gland with a resulting increase in production of pituitary regulating hormone can lead to peripheral endocrine gland hyperplasia. For example, if synthesis of thyroid hormone is defective, thyroid-stimulating hormone (TSH) is produced in excessive amounts, causing goiter.
Disease or drugs can cause increased rate of clearance of hormones. Circulating substances may also block the function of hormones. Abnormalities of the receptor or elsewhere in the peripheral endocrine tissue can also cause hypofunction.
Laboratory Testing for Endocrine Disorders
Because symptoms of endocrine disorders can begin insidiously and may be nonspecific, clinical recognition is often delayed for months or years. For this reason, biochemical diagnosis is usually essential; it typically requires measuring blood levels of the peripheral endocrine hormone, the pituitary hormone, or both.
Because most hormones have circadian rhythms, measurements need to be made at a prescribed time of day. Hormones that vary over short periods (eg, luteinizing hormone) necessitate obtaining 3 or 4 values over 1 or 2 hours or using a pooled blood sample. Hormones with week-to-week variation (eg, estrogen) necessitate obtaining separate values a week apart.
Blood hormone measurements
Blood hormone estimates
Free hormone levels can be estimated indirectly by assessing levels of the binding protein and using them to adjust levels of the total serum hormone. However, indirect methods are inaccurate if the binding capacity of the hormone-binding protein has been altered (eg, by a disorder).
In some cases, other indirect estimates are used. For example, because growth hormone (GH) secretion is pulsatile and GH has a short serum half-life, serum insulin-like growth factor 1 (IGF-1), which is produced in response to GH, is often measured as an index of GH activity. Whether measurement of circulating hormone metabolites indicates the amount of bioavailable hormone is under investigation.
Sometimes, instead of blood levels, urine (eg, free cortisol when testing for Cushing syndrome) or salivary hormone levels may be used.
Dynamic tests
In many cases, a dynamic test is necessary. Thus, in the case of hypofunctioning organs, a stimulation test (eg, ACTH stimulation) can be used. In hyperfunction, a suppression test (eg, ) can be used.
Treatment of Endocrine Disorders
Replacing deficient hormone
Suppressing excessive hormone production
Hypofunction disorders are usually treated by replacement of the peripheraldiabetes mellitus). Occasionally, a hormone-stimulating drug is used (eg, a sulfonylurea to stimulate insulin secretion).
Aging and Endocrinology
Hormones undergo many changes as a person ages.
Most hormone levels decrease.
Some hormone levels remain stable.
Some hormone levels increase.
Many aging-related changes are similar to those in patients with hormone deficiency. Replacing certain hormones in older adults can improve functional outcomes (eg, muscle strength, bone mineral density), but little evidence exists regarding effects on mortality. In some cases, replacing hormones may be harmful, as in an increase in risk of breast cancer with menopausal estrogen and progesterone therapy.
A competing theory is that the age-related decline in hormone levels represents a protective slowing down of cellular metabolism. This concept is based on the rate of living theory of aging (ie, the faster the metabolic rate of an organism, the quicker it dies). This concept is seemingly supported by studies on the effects of dietary restriction. Restriction decreases levels of hormones that stimulate metabolism, thereby slowing metabolic rate; restriction also prolongs life in rodents.
Specific age-related hormone decreases
Hormone levels that decrease with aging include
Dehydroepiandrosterone (DHEA) and DHEA sulfate
Estrogen
Melatonin
Pregnenolone
Testosterone
Dehydroepiandrosterone (DHEA) and DHEA sulfate levels decline dramatically with age. Despite optimism for the role of DHEA supplementation in older people, most controlled trials failed to show any major benefits.
Pregnenolone is the precursor of all known steroid hormones. As with DHEA, its levels decline with age. Studies in the 1940s showed its safety and benefits in people with arthritis, but additional studies failed to show any beneficial effects on memory and muscle strength.
Levels of growth hormone (GH) and its peripheral endocrine hormone (insulin-like growth factor 1 [IGF-1]) decline with age. GH replacement in older people sometimes increases muscle mass but does not increase muscle strength (although it may in malnourished people). Adverse effects (eg, carpal tunnel syndrome, arthralgias, water retention) are very common. GH may have a role in the short-term treatment of some undernourished older patients, but in critically ill undernourished patients, GH increases mortality. Secretagogues that stimulate GH production in a more physiologic pattern may improve benefit and decrease risk.
Levels of melatonin, a hormone produced by the pineal gland, also decline with aging. This decline may play an important role in the loss of circadian rhythms with aging.
Menopausal estrogen therapy is discussed under the treatment of menopause. in older men is discussed elsewhere.
Specific hormones that remain unchanged during aging
Hormone levels that remain stable as a person ages include
Adrenocorticotropic hormone (basal)
Cortisol (basal)
1,25-Dihydroxycholecalciferol
Estradiol (in men)
Insulin (sometimes increases)
Thyroid-stimulating hormone (TSH)
Thyroxine
Specific age-related hormone increases
Hormones that increase in relation to aging are associated with either receptor defects or postreceptor defects, resulting in hypofunction. These hormones include
Adrenocorticotropic hormone (ACTH—increased response to corticotropin-releasing hormone)
Activin (in men)
Atrial natriuretic factor
Cholecystokinin
Follicle-stimulating hormone
Gonadotropins (in women)
Norepinephrine
Sex-hormone binding globulin
Vasoactive intestinal peptide
Vasopressin (also loss of circadian rhythm)
