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SELECTIVE AND PARTIAL HYPOPITUITARISM

SELECTIVE AND PARTIAL HYPOPITUITARISM

Selective and partial hypopituitarism refers to the loss of at least one but not all pituitary hormones. The term panhypopituitarism is reserved for the syndrome resulting from the loss of all the hormonal functions of the pituitary, including those of the neurohypophysis (see Plates 1-16 and 1-27). The clinical presentation depends on the rapidity of hormone loss (e.g., sudden with pituitary apoplexy [see Plate 1-18] vs. slow with a slowly growing pituitary tumor) and the number of pituitary hormones affected.

The gonadotropic function of the pituitary is usually the first to fail, probably because the gonadotrophs are more sensitive to adverse conditions than are the other anterior pituitary cell types. In children with mild pituitary destruction, puberty is delayed or does not occur. If growth hormone is present in normal quantities and the other functions of the pituitary are not impaired, then overgrowth of the long hones will occur, and a eunuchoid body habitus will develop (see Plate 1-13). Men and women with acquired secondary hypogonadism typically present with slowly progressive symptoms (see Plate 1-14). Blood concentrations of testosterone in men and estradiol in women are below the reference ranges, and concentrations of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH)are inappropriately normal or low.

SELECTIVE AND PARTIAL HYPOPITUITARISM


Growth hormone (GH) deficiency also tends to occur early in patients with hypopituitarism, and the potential symptoms in adults (e.g., decreased sense of well-being, increased fat mass, decreased muscle mass) may be attributed to other causes, but with GH deficiency in childhood, a slowing of linear growth is typically evident. GH deficiency is evaluated by blood measurement of insulinlike growth factor 1 and GH response to provocation (e.g., insulin-induced hypoglycemia, arginine infusion, or growth hormone–releasing hormone administration).

With more severe insults to the pituitary gland, thyrotroph function and subsequently corticotroph function may be affected. Blood concentrations of thyroxine (total and free) are below the reference range, and thyrotropin (thyroid-stimulating hormone [TSH]) is inappropriately normal or low. The symptoms of primary hypothyroidism (see Plates 2-14 to 2-16) are indistinguishable from those of secondary hypothyroidism. In some instances, hypothyroidism-related symptoms may dominate the clinical picture, and treatment with levothyroxine in patients with concurrent secondary adrenal insufficiency may increase the clearance of the limited cortisol being produced, create an additional metabolic strain on the patient, and precipitate an adrenal crisis.

Secondary adrenal insufficiency differs from primary adrenal insufficiency in two important ways: (1) because of the loss of corticotropin (adrenocortico-tropic hormone [ACTH]) and melanocyte-stimulating hormone (MSH), pallor may be present that is not proportional to the moderate anemia sometimes seen, and (2) adrenal aldosterone secretion remains intact because the main regulators (angiotensin II and blood potassium) are not dependent on normal pituitary function. The blood concentration of cortisol measured at 8 am is below the reference range, nd ACTH is typically undetectable (see Plate 3-24).

Prolactin is frequently the most preserved pituitary hormone in patients with progressive hypopituitarism, and its absence may only be evident by the inability to lactate after delivery.

Selective loss of one pituitary hormone may also occur with lymphocytic hypophysitis—for example, these patients may present with selective ACTH deficiency. If the partial hypopituitarism is attributable to a pituitary or sellar mass, patients may also have symptoms related to tumor-specific pituitary hormone hypersecretion (e.g., acromegaly, hyperprolactinemia, or Cushing syndrome) or related to mass effect (e.g., vision loss, diplopia, or headache).

Typically, patients with single or multiple pituitary hormone deficiencies respond well to target hormone replacement therapy. If the causative lesion is not progressive, the prognosis for a long and active life is excellent.