Hypopituitarism — Symptoms, Diagnosis and Treatment

 Image : “Inauguración del Hospital Municipal de Chiconcuac” by Presidencia de la República Mexicana.  License: CC BY-SA 2.0 

Recap: Pituitary — Anatomy and Hormones

Definition of the Pituitary Gland

The pituitary gland, the master of all endocrine glands, is physiologically divided into two larger lobes: anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis). Pars Intermedia is a small relatively avascular zone that lies between the anterior and posterior lobe. It is rudimentary in nature. The anterior pituitary constitutes 80% of the gland. A hypothalamohypophyseal portal vascular system carries positively and negatively acting factors from the hypothalamus to the anterior pituitary.

Image: “Hypothalmo-Hypophyseal Portal Vascular of Anterior Pituitary” by Philschatz. License: CC BY 4.0

The posterior pituitary consists of modified glial cells termed pituicytes. Axonal terminals called a hypothalamohypophyseal tract, extending from the hypothalamus through the pituitary stalk to the posterior lobe, regulates neurohypophysis hormonal regulation. These axonal terminals of the posterior pituitary store the hormones (synthesized in the hypothalamus) and release them on appropriate stimulus.

Image: “Hypothalamo-Hypophyseal Tract of Posterior Pituitary” by Phil Schatz. License: CC-BY 4.0

Hormones of Anterior Pituitary

Hormones of Posterior Pituitary

Hypothalamus Control of Pituitary

Embryological Origin

Anterior pituitary, ectodermal in origin, develops from Rathke’s pouch, which is an upward invagination of oral ectoderm from the roof of the stomodeum; in contrast, the neurohypophysis develops from the infundibulum, which is a downward extension of neural ectoderm from the floor of the diencephalon.

Hypopituitarism

A clinical situation characterized by a deficiency in the pituitary hormone production, which results from disease of the hypothalamus or pituitary itself. Hypofunction occurs when approximately 80% of pituitary parenchyma is lost.

Etiology of Hypopituitarism

Structural defect

• Rathke’s cleft cyst
• Meningioma
• Craniophyrangioma
• Pituitary adenoma/tumors

Inflammatory causes

• Sarcoidosis
• Wegener granulomatosis
• Hemochromatosis

Congenital

• Kallman’s syndrome (GNRH deficiency)
• Hypoplasia of pituitary

Traumatic

• Head injury
• Sellar surgery
• Radiotherapy

Infections

• Tuberculosis
• Syphilis
• Encephalitis

Vascular

• Sheehan’s syndrome (Post-Partum Pituitary necrosis)
• Carotid artery aneurysm
• Subarachnoid hemorrhage

Epidemiology of Hypopituitarism

The first study on the prevalence and incidence of hypopituitarism in adults was conducted in northwestern Spain. It showed an average annual incidence rate of hypopituitarism of 4.21 cases/100,000 with this incidence being similar for both sexes. The cause of hypopituitarism was a pituitary tumor in 61%, a non-pituitary tumor in 9% and a non-tumor cause in 30%. Around 50% of patients had 3-5 pituitary hormonal deficiencies, with LH/FSH being the most prevalent.

A higher risk of chronic hypopituitarism was found after traumatic brain injury and intrasellar aneurysms.

Image: “Endocrine glands and cells are located throughout the body and play an important role in homeostasis.” by Philschatz. License: CC BY 4.0

Pathophysiology of Hypopituitarism

Damage to the pituitary gland results in a decreased target gland hormone production. There is a sequential loss of anterior pituitary hormones secondary to mass effect, occurring initially with a deficiency of Gonadotropins (LH and FSH), followed by a loss of ACTH and TSH.

Isolated deficiencies of LH, FSH, GH, ACTH, and TSH can also be seen. If the cause of decreased hormone production is direct damage to the pituitary, an increased amount of hypothalamic releasing hormones may be seen on blood examination.

Pituitary adenomas may present insidiously with a tumor compressing the surrounding pituitary tissue, or causing impaired blood flow to the normal cells by interfering with the hypothalamus-hypophyseal portal system, resulting in hypopituitarism.

Pituitary apoplexy describes a sudden onset of neurological impairment, including visual disturbance, ophthalmoplegia (III, IV, VI cranial nerve involvement) or an excruciating headache due to bleeding into or impaired blood supply of the pituitary gland. In severe cases, it can cause cardiovascular collapse, loss of consciousness and even sudden death.

Sheehan Syndrome

Sheehan Syndrome (post-partum ischemic necrosis) is a frequently asked USMLE question. The clinical scenario will point toward a pregnant female with a bad obstetric history.

During pregnancy, the anterior pituitary enlarges to almost twice its original size. This physiological expansion is not accompanied by an increase in blood supply; there is relative anoxia of pituitary tissue. A further reduction in blood supply, due to post-partum hemorrhage, may precipitate infarction of the anterior pituitary. Posterior pituitary, due to its direct blood supply, is less susceptible to ischemic injury. The patient usually presents with complaints of inability to feed the baby, fatigue, and lethargy.

Symptoms of Hypopituitarism

Symptoms, due to compression, include a headache, visual field defects, and diplopia; this point towards an intracranial pathology. Compression of optic chiasma, which is adjacent to the pituitary, can result in bitemporal homonymous hemianopia.

Diagnosis of Hypopituitarism

After the clinical findings have been established, the laboratory diagnosis may deliver further indications that may support the suspected diagnosis:

1. Basal blood and stimulation tests

• ACTH Deficiency: basal cortisol and ACTH level, short ACTH stimulation test
• Growth hormone deficiency: growth hormone levels stimulation and suppression tests, serum insulin-like growth factor-1, insulin tolerance test
• TSH Deficiency: basal T3 & T4 levels, serum TSH level
• LH/FSH deficiency: serum levels of LH, FSH, and testosterone
• ADH deficiency: water deprivation test

2. Brain imaging

• MRI or CT scan to detect pituitary tumors or any other intracranial pathology.
  

  Image: “CT of a craniopharyngioma.” by Matthew R Garnett, Stéphanie Puget, Jacques Grill, Christian Sainte-Rose. License: CC-BY 2.0

3. Vision tests

• To detect any defects in the visual field due to the compression of the optic chiasma.

Differential Diagnosis of Hypopituitarism

• Hyponatremia
• Kallman syndrome (idiopathic hypogonadotropic hypogonadism (IHH))
• Polyglandular autoimmune syndrome
• Septo-optic dysplasia
• Hypothyroidism
• Pituitary macroadenomas

Therapy of Hypopituitarism

Management of acute hypopituitarism

Emergency treatment comprises the following three drastic measurements after cardiopulmonary stability:

1. Replace deficient hormone: hydrocortisone in a stress dose is the standard of choice to replace the glucocorticoid deficiency, followed by IV levothyroxine for thyroid hormone replacement.
2. Treatment of the electrolyte and cardiovascular effects due to missing hormones
3. Antibiotics should be used to treat underlying infection or sepsis.

In-patient management

• Treat the underlying cause, if any, like tumors (get neurosurgical consultation)
• Replacement of hormones is the ultimate treatment of panhypopituitarism. This is done by administering:
  • Hydrocortisone for adrenal insufficiency
  • Thyroxine for thyroid hormone replacement
  • Growth hormone by daily injections in children (discontinued after epiphysis are fused)
  • Testosterone and estradiol for male and female hypogonadism
  • Desmopressin (DDAVP) tablets or nose spray for ADH replacement
  • Dopamine agonist (cabergoline) for prolactin inhibition

  When fertility is desired, HCG, purified or biosynthetic gonadotropin or pulsatile GnRh is given.

  Prognosis of Hypopituitarism

  Mortality in patients with hypopituitarism is significantly increased. The only significant independent predictive factors for survival are an age at diagnosis and hypogonadism.
  A recent study suggested that females with hypopituitarism have a high incidence of cardiovascular morbidity and an increased prevalence of cardiovascular risk factors.