PANCE Blueprint Endocrinology (7%)

Diseases of the Pituitary Gland (PEARLS)


Acromegaly/gigantism Etiology: Gigantism and acromegaly are usually caused by a pituitary adenoma that secretes excessive amounts of Growth Hormone; rarely, they are caused by non-pituitary tumors that secrete GHRH

  • Gigantism occurs if growth hormone (GH) hypersecretion begins in childhood, before closure of the epiphyses
  • Acromegaly involves growth hormone GH hypersecretion beginning in adulthood; a variety of bony and soft tissue abnormalities develop

Presentation:

  • Large hands, feet, nose, lips, ears, jaw, tongue
  • Presents as gigantism (excessive height) if occurs before epiphyseal closure

Diagnosis:

  • GH test 2 hour after glucose load
  • Increased IGF-1
  • MRI/CT shows pituitary tumor

Treatment: Pituitary tumor removal

Diabetes insipidus (ReelDx) Diabetes insipidus (DI) is caused by a deficiency of or resistance to vasopressin (ADH), which decreases the kidneys' ability to reabsorb water, resulting in massive polyuria

  1. Central diabetes insipidus - Deficiency of ADH from posterior pituitary/hypothalamus
    • No ADH production most common type: idiopathic, autoimmune destruction of posterior pituitary from head trauma, brain tumor, infection, or sarcoidosis
  2. Nephrogenic diabetes insipidus - Lack of reaction to ADH
    • Partial or complete insensitivity to ADH: caused by drugs (Lithium, Amphoterrible), hypercalcemia and hypokalemia affect the kidney's ability to concentrate urine, acute tubular necrosis

Diagnosis:

  • 24 hr urine –specific gravity 1.006
  • Vasopressin challenge test (central DI)

Serum osmolality (concentration) is high (unable to stop secretion of water into the kidneys so blood becomes more concentrated) and urine osmolality is low because it is so dilute

The water deprivation test is the simplest and most reliable method for diagnosing central diabetes insipidus but should be done only while the patient is under constant supervision. Serious dehydration may result

  • Normal response is progressive urine concentration
  • Diabetes insipidus results in continued production of dilute urine despite water deprivation

Treatment:

  • Central – desmopressin
  • Nephrogenic— indomethacin +/- HCTZ, desmopressin
Pituitary dwarfism Etiology: Achondroplasia (FGFR3 mutation)

  • The pituitary gland does not make enough GROWTH HORMONE

Presentation: Short stature/limbs, prominent brow, midfacial hypoplasia

Labs: ↓ GH, ↓ IGF1

BONE AGE: The primary symptom of pituitary dwarfism is lack of height. Therefore, a change in the individual's growth habits will help lead to a diagnosis.

  • X-ray the child's hand to determine the child's bone age by comparing this to the child's actual chronological age.

Treatment:

If dwarfism is due to decreased human growth hormone, and not due to a primary skeletal disorder, the child can be treated with human growth hormone treatments to try and stimulate normal growth.

Surgery may be necessary to remove a pituitary adenoma if that is the cause of the dwarfism.

Pituitary adenoma and Pituitary neoplastic disease A 39-year-old woman with bilateral milky breast discharge decreased lateral vision fields, and pituitary mass (prolactinoma)

Most common tumors are microadenomas that are functional (hypersecretion of pituitary hormones), nonfunctional or compressive

  • Microadenomas are less than 1 cm in diameter, whereas adenomas that are 1 cm or more are commonly referred to as macroadenomas
    • Microadenoma < 10 mm
    • Macroadenoma > 10 mm

Diagnosis:

  • MRI is the study of choice to look for sellar lesions/tumors
  • Endocrine studies: Prolactin, GH, ACTH, TSH, FSH, LH
Classification of Pituitary Adenomas
Tumor Type Secretory Product(s) Relative Frequency (%)
1. Prolactinoma (Galactorrhea)

  • Most common
  • Secrete prolactin
  • Presentation: Galactorrhea, infertility, amenorrhea
  • Treatment: Bromocriptine
↑ Prolactin 50%
2. Somatotroph Adenoma (Acromegaly)

  • Secrete GH
  • Presentation: Acromegaly
  • Treatment: Resection is first line
↑ Growth Hormone/Prolactin 10%
3. Corticotroph Adenoma (Cushing's Syndrome)

↑ ACTH 5%
4. Thyrotroph Adenoma (Hyperthyroidism)

↑ TSH 1%
5. Nonsecreting Adenoma

  • Null Cell - No secretion
(α) alpha -subunit 34%
posterior-pituitary_5682_1476761567 The posterior pituitary is an endocrine gland primarily composed of the nerve terminals of axons extending from the hypothalamus. It is important in the neuroendocrine reflex, which occurs when sensory neurons are stimulated resulting in action potential in hypothalamic cells and exocytosis of hormones from the posterior pituitary. Vasopressin is one of the hormones released from the posterior pituitary. Vasopressin is synthesized in the hypothalamus but stored in the posterior pituitary and released in response to synaptic input from osmoreceptors that detect increased osmolality of blood plasma. This hormone affects the kidney into retaining more water and also can constrict blood vessels. The second hormone released from the posterior pituitary is Oxytocin. It is released via a neuroendocrine reflex in response to stimulation of the nipples during breastfeeding that causes the mammary glands to contract and release milk. Stimulation of the nipples causes action potential generation in the oxytocin cells of the hypothalamus, which travels down to the nerve endings in the posterior pituitary and results in the exocytosis of Oxytocin. It also causes uterine smooth muscle contraction during the second and third stages of labor.

Posterior Pituitary Picmonic

anterior-pituitary_5186_1477332872 The anterior pituitary is an endocrine gland that releases a variety of hormones in response to stimulus from the hypothalamus and other sources. ACTH, adrenocorticotropic hormone, stimulates the adrenal glands into releasing cortisol. FSH and LH both stimulate the gonads (ovaries and testes). FSH (follicle-stimulating hormone) regulates reproductive processes, sexual maturation, development, and growth. LH stimulates the ovaries and testes into producing estrogen and progesterone, and testosterone respectively. Thyroid-stimulating hormone (TSH) stimulates the thyroid gland into producing thyroxine (T4) and triiodothyronine (T3), both of which stimulate metabolism in most tissues. Prolactin is a peptide hormone that stimulates milk production from the mammary glands and can affect levels of sex hormones. The other hormones released, but not shown here, are endorphins, which are released in response to exercise, pain, and excitement and cause a feeling of analgesia (well-being). Finally, growth-hormone stimulates cell reproduction, development, and growth.

Anterior Pituitary Picmonic

Hypoparathyroidism (Prev Lesson)
(Next Lesson) Acromegaly/gigantism (Growth Hormone)
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