Weatherly's Woes - Pituitary Gland

GROWTH HORMONE

Growth Hormone has a helpful, if uncreative, name. It helps all of your organs grow big and strong! For whatever reason, diseases related to GH are rare.

LARON SYNDROME is a very rare example of a growth hormone “deficiency” that causes dwarfism (250 known cases). It is typically due to defective GH receptors. They have elevated GH levels, but low IGF-1 levels.

ACROMEGALY & GIGANTISM

Growth hormone excess

Acromegaly and Gigantism are due to GH excess, usually caused by a GH-secreting pituitary adenoma (which might also cause bitemporal hemianopsia). Diagnosed by (a) very high levels of IGF-1 or (b) when drinking glucose doesn’t suppress their GH or IGF-1 levels like it normally should (Glucose Suppression Test). If there isn’t a pituitary tumor on their MRI, then consider GH abuse (used by wannabe beefcakes alongside anabolic steroids). Medical therapy includes somatostatin analogs (Octreotide), GH blockers (Pegvisomant) or dopamine agonists (Cabergoline). Cardiomegaly is the most common cause of death.

GIGANTISM makes people very tall and with proportionally enlarged organs. If the adenoma onsets before puberty (when the epiphyseal plates close), then Gigantism will occur. Andre the Giant was a famous wrestler-turned-actor who had gigantism. He was 7’4”, weighed over 500 pounds and wore size 58 shoes!

ACROMEGALY occurs if the adenoma onsets after puberty (the growth plates have already closed). Once the growth plates close, the long bones cannot grow any larger via endochondral ossification. But many smaller bones grow using intramembranous ossification instead, and these bones will grow large in Acromegaly. Examples include bones of the skull, hands and feet. The symptoms are identical to Gigantism, EXCEPT for the height.

HYPOPITUITARISM

Hypopituitarism refers to an overall state of low pituitary hormone production.

NON-SECRETORY PITUITARY ADENOMAS are a common cause of this. A tumor can squish all of the pituitary cells. Therefore, hormones produced in the pituitary gland (ACTH, TSH, GSH, GnRH) stop being secreted, and multiple hormonal axes decline. Note that prolactin levels often rise with pituitary tumors, because its inhibitory supply of dopamine is interrupted. Simultaneously any pituitary tumor will smush the optic chiasm, causing bitemporal hemianopsia (tunnel vision). The symptoms of an adenoma are often gradual and mild. Tumors larger than 10mm are typically removed surgically (through the nose!).

PITUITARY APOPLEXY is a spontaneous hemorrhage of the pituitary. It’s usually seen when someone has an unsustainably large adenoma, which outgrows its own blood supply and undergoes necrosis.

CRANIOPHARYNGIOMAS are one of the most common pituitary tumors, and they’re especially common in kids. Unlike adenomas, craniopharyngiomas do not arise from normal pituitary tissue. Rather, it arises from the remnants of Rathke’s pouch (a piece of nasopharyngeal tissue that climbs up towards the brain in utero). Symptoms include a headache (intracranial mass), bitemporal hemianopsia (optic chiasm compression) and endocrine problems. High yield! There are three diagnostic tests:

(1) MRI showing a calcified suprasellar mass

(2) Biopsy shows calcification and cholesterol crystals inside a “motor oil-like” fluid

(3) Stimulation tests (give GnRH for LH/FSH) will result in less-than-expected elevations.

SHEEHAN SYNDROME is pituitary ischemia that follows postpartum hemorrhage. The pituitary gland doubles in size during pregnancy (lots of Estrogen, Prolactin and Oxytocin are needed), but the blood supply remains unchanged. So if there is postpartum hemorrhage, the pituitary gland is susceptible to watershed ischemia and necrosis. Suspect this if a mother with a complicated delivery complains of inability to lactate (no prolactin), menstruate after she stops breastfeeding (no estrogen) or tolerate the cold (no thyroid hormone).

EMPTY SELLA SYNDROME is a mysterious phenomenon where the pituitary gland suddenly disappears in adulthood! On an MRI, the gland is replaced by CSF. Possible theories include compression or atrophy. More common in obese women.

ANTIDIURETIC HORMONE (ADH)

The conserve-water hormone

DIABETES INSIPIDUS (DI) refers to a state of low ADH activity. They pee out all of their water. It causes voluminous watery pee and hypernatremia. DI means “tasteless drain” in Latin, which is in contrast to diabetes mellitus which refers to sweet urine.

Central DI refers to low levels of ADH. It sometimes occurs following head injuries or whenever there is pituitary stalk trauma. Replace their ADH with the ADH-analog Desmopressin.

Nephrogenic DI refers to a state of dysfunctional ADH V2 receptors (recall that V1 receptors are found on blood vessels and cause vasoconstriction). Nephrogenic DI is usually caused by lithium or hypercalcemia. Treat with Indomethacin (less GFR → less pee), HCTZ (this paradoxical treatment helps you lose sodium). If you give desmopressin, Central DI will improve but Nephrogenic DI will not.

SYNDROME OF INAPPROPRIATE ADH (SIADH) is an aptly named disease where there is too much ADH being made. It causes dark pee and hyponatremia. Hyponatremia can cause neurological symptoms. There are a lot of causes, including ectopy (small cell lung cancer), drugs (carbamazepine, SSRIs, vincristine, vinblastine, cyclophosphamide) or infections (lung abscess). Treat with V2 Blockers like Conivaptan or Tolvaptan.