What Are Neuroendocrine Disorders?
They are metabolic disorders that arise due to alterations in the endocrine function of the brain. Different parts, directly and indirectly, perform the endocrine function of the brain; some of them are the hypothalamus, the pituitary, the pineal gland, etc.
The hypothalamus is considered the most important because the pituitary and the pineal gland produce and release hormones based on their direction. The hypothalamus has three functions:
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Serves as the head ganglion of the autonomic nervous system.
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Controls the circadian and seasonal clock.
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It works as the neural center for the endocrine system.
The hypothalamus releases certain hormones that coordinate different bodily functions by carrying messages through the blood to the various organs and organ systems. Some of the hormones released by the hypothalamus are-
1. Thyrotropin-Releasing Hormone (TRH) - It is one of the smallest hormones in the body; it is made by a cluster of nerves (collectively known as the paraventricular nucleus) in the hypothalamus.
The paraventricular nucleus is situated just above the pituitary gland - A small pea-sized endocrine gland that secretes hormones like the thyroid-stimulating hormone, growth hormone, follicle-stimulating hormone, etc.
The nerve fibers of the paraventricular nucleus carry the TRH from the cluster and into the blood surrounding the pituitary gland. The TRH then regulates the formation and secretion of the thyroid-stimulating hormone by the pituitary, which in turn regulates the production of thyroid hormones by the thyroid gland.
2. Growth Hormone-Releasing Hormone (GHRH) - Similar to TRH, the GHRH secreted by the hypothalamus stimulates the pituitary gland to produce and release growth hormone into the bloodstream which then acts on every tissue of the body to control metabolism and growth.
The hypothalamus also produces a hormone called somatostatin which counteracts the action of GHRH - an autoregulatory feature of the hypothalamus.
3. Corticotropin-Releasing Hormone - Also released by the paraventricular nucleus of the hypothalamus, this hormone has several important functions. They are:
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It acts as the central driver of the stress hormone system.
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It is also responsible for stress-related responses in the body, like reducing appetite, increasing anxiety, improving memory and selective attention, etc.
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It has been known to play an important role in inducing labor.
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It also is responsible for producing swelling and tenderness during inflammation.
4. Gonadotropin-Releasing Hormone - Secreted by highly specialized cells in the hypothalamus, this hormone stimulates the pituitary hormone to release the follicle-stimulating and luteinizing hormones, both of which act on the ovaries and the testes to maintain the reproductive function, respectively.
5. Prolactin Inhibition - The hypothalamus produces dopamine, which regulates prolactin- a hormone produced by the pituitary and is responsible for the growth of the breast and the production of milk during pregnancy and after birth.
Besides the functions mentioned above, the hypothalamus also controls the neurohypophysis of the pituitary and pineal glands. The former is responsible for the secretion of hormones oxytocin (essential for childbirth and breastfeeding) and vasopressin (antidiuretic), and the latter secretes melatonin, which aids in sleep.
What Causes Neuroendocrine Disorders?
Disturbances in the neuroendocrine functions of the hypothalamus and pituitary can occur due to conditions like tumors, trauma, malnutrition, congenital, etc. This leads to various types of neuroendocrine disorders, some of which are-
1. Global Hypothalamic Syndrome - It is a condition characterized by complete loss of the hypothalamic function. A variety of lesions or conditions can invade or destroy the hypothalamus; some of them are as follows:
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Sarcoidosis - It is a multisystem granulomatous disorder that can affect the hypothalamus and the pituitary leading to a condition called hypothalamic-pituitary sarcoidosis. It involves patchy destruction of the hypothalamic-pituitary tract, resulting in various combinations of anterior and posterior pituitary hormone dysfunction.
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Tumors - A few tumors that can cause complete dysfunction of the hypothalamus and the pituitary are metastatic carcinoma, lymphoma, craniopharyngioma, germinomas, teratomas, etc.
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Inflammatory Conditions - Inflammatory conditions known to cause neuroendocrine dysfunction are infundibuloneurohypophysitis, histiocytosis X, and rarely the Erdhein-Chester disease.
2. Partial Hypothalamic Syndrome - These disorders develop due to the loss of one function of the hypothalamus. A classic example of this is diabetes insipidus, which is a state of polyuria (excess urine) with dilute urine and polydipsia (excessive thirst) that results due to the loss of activity of antidiuretic hormone (vasopressin).
3. Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) - It is a condition in which the body makes too much antidiuretic hormone leading to too much water in the blood and concentrated urine.
4. Nelson Syndrome - It is a neuroendocrine disorder characterized by abnormal hormone secretion, enlargement of the pituitary, and the development of large and invasive growth known as adenomas.
5. Pituitary Insufficiency - Also known as hypopituitarism, it is a condition where the affected individual will have a short supply of one or more of the pituitary hormones.
6. Precocious Puberty- This condition is characterized by premature development of secondary sexual characteristics. It is typically caused due to a hamartoma of the hypothalamus, which is an associated complication of Von Recklinghausen disease and polyostotic fibrous dysplasia of McCune-Albright syndrome.
7. Froehlich Syndrome - Also known as adiposogenital dystrophy, it is a classical example of delay or failure of puberty caused due to injury of a part of the hypothalamus.
Individual genetic variations known as constitutional delay of growth and puberty (CDGP), or other functional defects, such as undernutrition or chronic illness, also affect the neuroendocrine function of the hypothalamus. A few examples of such conditions are diencephalic syndrome, anorexia nervosa, Prader-Willi syndrome, neuroleptic malignant syndrome, etc.
How Are Neuroendocrine Disorders Treated?
The treatment depends on the cause of the underlying conditions; for example, for disorders caused due to tumors, surgical removal of the tumor along with medication helps to improve the condition.
However, neuroendocrine disorders caused due to genetic abnormalities or trauma cannot be treated with the help of surgery. On the other hand, if the disorder is due to the under secretion of the hormone, hormone replacement therapy will help address the condition. If the disorder is caused due to oversecretion, then it can be managed with diet restriction, medication, selective surgery, radiation therapy, etc.
Conclusion
Most neuroendocrine disorders result from neuroendocrine tumors or treatments done to remove them. Diagnosis can be made with the help of physical examination, past medical history, and laboratory investigations. Early recognition and appropriate management will help to improve the prognosis and prevent long-term complications.
