Hypopituitarism

Summary

Hypopituitarism is a dysfunction of the pituitary gland, during which it fails to produce a sufficient amount of one or more hormones. The pituitary gland is part of the endocrine system and is responsible for producing hormones. The pituitary gland is small bean sized gland, located at the base of the brain. It regulates hormone production that is responsible for several bodily functions, including blood pressure, reproduction, and growth.

Associated Anatomy

The pituitary gland is comprised of two parts.  The anterior pituitary, also called adenohypophysis, which receives signals from the hypothalamus to normalize the secretion of the pituitary hormones. Some of the hormones secreted by the anterior pituitary gland are: thyrotropin, gonadotropins: (follicle-stimulating hormone, FSH and luteinizing hormone, LH), somatotropin (GH), corticotropin (ACTH), and prolactin. The posterior pituitary does not produce its own hormones, instead it stores two hormones, vasopressin (VP) and oxytocin (OXT), produced by the hypothalamus. The posterior pituitary then releases these hormones into circulation when needed.

Causes

Hypopituitarism may result from several different causes, such as a congenital defect, tumor or inflammation of the pituitary gland, brain surgery, radiation treatment, head injuries, or lack of blood flow to the brain.  Infections of the brain such as meningitis may also cause hypopituitarism.

Epidemiology

Hypopituitarism has an estimated incidence rate of 4.2 cases per 100,000 internationally, without gender differences.

Pathophysiology

Target gland hormone is reduced by any impairment in pituitary hormone production. This process occurs due to a lack of trophic stimulus. In normal function subphysiologic target hormone levels stimulate the pituitary gland to produce trophic hormone production. In hypopituitarism this response becomes decreased or abnormal.

Symptoms

Symptoms of hypopituitarism may vary depending on which hormone is under produced.  Newborns with congenital hypopituitarism usually have “pan-hypopituitarism” where all of the hormones produced by the anterior pituitary gland are impaired and therefore can present with atypical genitalia (micropenis), hypoglycemia (low blood sugar), seizure, failure to thrive. Impact to the posterior pituitary gland results in central diabetes insipidus.

Children who develop hypopituitarism due to intracranial lesions or radiation tend to lose complete function of the anterior and posterior pituitary glands.

More commonly, children develop “isolated” pituitary deficiencies, such as growth hormone deficiency (with otherwise normal pituitary gland function). Growth hormone deficiency affects both children and adults. Children may experience slow growth, an increase in body fat, low energy, decreased muscle mass, as well as higher risk for cardiovascular diseases.

Corticotropin (ACTH) deficiency (Cushing Disease) may present symptoms such as fatigue, weight loss, and low blood pressure. The severity of the symptoms may also be affected by stress and physical illness. In cases of deficiency of the thyroid-stimulating hormone, patients may experience weight gain (or loss), anemia, hair loss, constipation and depression. Lack of production of the luteinizing hormone (LH) as well as the follicle-stimulating hormone (FSH) would result in lack (or cessation) of puberty. Women may experience irregular periods and infertility, while men may experience erectile dysfunction and infertility. Both, men and women may also suffer from osteoporosis, resulting in weaker bone structure.

Typical Test

A blood test is used to measure basal pituitary and target hormone levels. Growth hormone (GH) and adrenocorticotropic hormone (ACTH) deficiency can be measured by a stimulation or dynamic test, in which the patient will be given hormonal stimulation medicine before the test. An additional brain MRI may determine if there is a tumor present on the pituitary gland, along with a vision test that can determine if the tumor has impaired vision functions.

Differential Diagnoses

Several other conditions may present similar symptoms to hypopituitarism. Some of these conditions are: hypothyroidism, primary adrenal insufficiency, hyponatremia, Kallmann Syndrome and idiopathic hypogonadotropic hypogonadism, pituitary macroadenomas, septo-optic dysplasia, and type I, II, III Polyglandular Autoimmune Syndrome

Possible Treatment

Treatment for hypopituitarism would require hormonal replacement therapy. Hormonal replacement therapy may include corticosteroids, which would replace adrenal hormone (cortisol), as well as levothyroxine for low thyroid hormone levels. It is also important to wear a medical alert bracelet indicating of the condition, especially in cases of an ACTH deficiency, where a patient may be required corticosteroids in an emergency situation. Regular monitoring with your physician during the duration of hormonal replacement therapy is recommended.

Expected Prognosis

Patients diagnosed with hypopituitarism can lead a normal lifestyle, provided maintain stable treatment and regularly consult with their physician.

Risk Factors

Patients diagnosed with hypopituitarism with a deficiency of ACTH may be at an increased risk for an onset of an adrenal crisis, and as a precaution should wear/carry a bracelet stating their condition in case of an emergency. Cardiovascular disease risk, as well as an increased susceptibility to infections, are often higher for patients diagnosed with hypopituitarism.

Studies

Studies on the role of genetics in hypopituitarism have provided advances in treatment options. Studies have also shown that one of the causes of hypopituitarism may be distinctive vascularization of the pituitary gland, especially by disruption of the long vessel connection between the hypothalamus and the pituitary. New drugs and autoimmune diseases are looked into as possible causes of hypopituitarism. Several new drugs: ipilimumab, have been suspected to cause hypopituitarism.  There are also studies on new diagnostic tools, as well as clinical trials for growth hormone stimulants.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5325066/

https://www.ncbi.nlm.nih.gov/books/NBK278989/

 

Useful Resources

https://www.mayoclinic.org/diseases-conditions/hypopituitarism/symptoms-causes/syc-20351645

https://www.hormone.org/diseases-and-conditions/pituitary/hypopituitarism

https://www.pituitarysociety.org/patient-education/pituitary-disorders/hypopituitarism/what-are-the-symptoms-of-hypopituitarism

 

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