Hypopituitarism
meduploader - 06-29-09 15:23

Diminished or absent secretion of one or more pituitary hormones. Etiologies are outlined below.
Presentation depends on the particular hormone deficiency. In increasing order of importance, with ACTH being preserved the longest, pituitary hormones are lost as follows:
GH deficiency: May be asymptomatic in adults. Has been associated with ↑ fat mass, bone loss, cardiovascular risk factors, and possibly reduced quality of life.
LH/FSH deficiency: Hypogonadism. Manifested in men as lack of libido and impotence and in women as irregular menses/amenorrhea.
TSH deficiency: Hypothyroidism.
ACTH deficiency: AI (weakness, nausea, vomiting, anorexia, weight loss, fever, and hypotension). Hyperkalemia is generally present only in 1° AI.
ADH deficiency (DI) is seen only if the posterior pituitary is also involved.
DIFFERENTIAL
Remember the “eight I’s”: Invasive, Infiltrative, Infarction, Injury, Immunologic, Iatrogenic, Infectious, Idiopathic.
Invasive causes: Pituitary adenomas (usually nonproductive macroadenomas), craniopharyngioma, 1° CNS tumors, metastatic tumors, anatomic malformations (e.g., encephalocele and parasellar aneurysms).
Infiltrative causes: Sarcoidosis, hemochromatosis, histiocytosis X.
Infarction:
Sheehan’s syndrome: Pituitary infarction associated with postpartum hemorrhage and vascular collapse. Typically presents with difficulty in lactation and failure to resume menses postpartum.
Pituitary apoplexy: Spontaneous hemorrhagic infarction of a preexisting pituitary tumor.
Injury: Severe head trauma can lead to anterior pituitary dysfunction and DI.
Immunologic causes: Lymphocytic hypophysitis. During or just after pregnancy, 50% of patients have other autoimmune disease.
Iatrogenic: Most likely after pituitary surgery or radiation therapy.
Infectious: Rare; include TB, syphilis, and fungi.
Idiopathic: Empty sella syndrome.
The subarachnoid space extends into the sella turcica, partially filling it with CSF and flattening the pituitary gland. Due to congenital incompetence of the diaphragma sellae (the most common cause) or to pituitary surgery, radiation therapy, or pituitary infarction.
Check for hormone deficiencies and hyperprolactinemia, but most patients who have a radiologic diagnosis have normal pituitary function and do not require treatment.
DIAGNOSIS
Specific hormonal testing includes the following:
ACTH/adrenal axis: Abnormal ACTH and cortisol. Note that the test may be normal
in acute pituitary dysfunction, since in this setting, the adrenals can still respond to a pharmacologic dose of ACTH.
Thyroid axis: Low free T4 (TSH levels are not reliable for this diagnosis, as levels may be low or normal) in 2° hypothyroidism.
Gonadotropins: Low FSH/LH, testosterone, or estradiol.
GH: Low IGF-1, GH provocative testing.
ADH
TREATMENT
Treat the underlying cause. Medical treatment consists of correcting hormone deficiencies:
ACTH: Hydrocortisone 10–30 mg/day, two-thirds in the morning and onethird in the afternoon/evening.
TSH: Replace with levothyroxine (adjust to a goal of normal free T4).
GnRH:
Men: Replace testosterone by injection, patch, or gel.
Women: If premenopausal, OCPs or HRT.
GH: Human GH is available.
ADH: Intranasal DDAVP 10 μg QD-BID.
Seventy-five percent or more of the pituitary must be destroyed before there is clinical evidence of
hypopituitarism.