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.
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.
