PITUITARY GIGANTISM
Pituitary gigantism occurs when a growth hormone (GH)–secreting pituitary tumor develops before fusion of the epiphyseal growth plates in a child or adolescent. In contrast, when GH-secreting pituitary tumors develop in an adult (after complete epiphyseal fusion), there is no linear growth, but there are acral changes, and the condition is termed acromegaly (see Plate 1-20). Pituitary gigantism is rare. When it starts in infancy, it may lead to exceptional height. The tallest well- documented person with pituitary gigantism measured 8 ft, 11 in (272 cm). When untreated, pituitary giants are typically taller than 7 ft. The GH-secreting pituitary tumors in individuals with pituitary gigantism are usually sporadic, but they may arise as part of a syndrome such as multiple endocrine neoplasia type 1 (see Plate 8-1), McCune-Albright syndrome (see Plate 4-11), and the Carney complex (see Plate 3-12).
Although usually caused by a
pituitary GH-secreting adenoma, pituitary gigantism may also be caused by an
ectopic tumor secreting GH-releasing hormone (GHRH) or by hypothalamic
dysfunction with hypersecretion of GHRH.
In addition to the accelerated
linear growth, patients with pituitary gigantism may slowly develop many of
those features seen in adults with acromegaly—for example, soft tissue
overgrowth, progressive dental malocclusion (underbite), a low-pitched voice,
head- aches, malodorous hyperhidrosis, oily skin, proximal muscle weakness,
diabetes mellitus, hypertension, obstructive sleep apnea, and cardiac
dysfunction. The mass effects of GH-producing pituitary macroadenomas (10 mm)
are similar to those of other pituitary macroadenomas—they include visual field
defects, oculomotor pareses, headaches, and pituitary insufficiency.
It is important to note that most
children with accelerated linear growth do not have pituitary gigantism. More
common causes of tall stature include precocious puberty, genetic tall stature,
and hyperthyroidism.
High plasma GH levels are not
diagnostic of pituitary gigantism. The diagnosis of pituitary gigantism should
be considered in patients after other causes of accelerated linear growth have
been excluded. The biochemical diagnosis is based on two criteria: a GH level
that is not suppressed to less than 0.4 ng/dL after an oral glucose load
(75–100 g) and an increased serum concentration (based on normal range
adjusted for age and gender) of insulinlike growth factor 1 (IGF-1). Serum
prolactin concentrations should also be measured because the pituitary neoplasm
in children frequently arises from the mammosomatotroph, so cohypersecretion of
prolactin may occur. The laboratory assessment of pituitary gigantism is
supplemented with magnetic resonance
imaging (MRI) of the pituitary and visual field examination by quantitative
perimetry. If imaging of the pituitary fails to detect an adenoma, then plasma
GHRH concentration and CT of the chest and abdomen are indicated in search of
an ectopic GHRH- producing tumor (e.g., pancreatic or small cell lung
neoplasm).
Treatment is indicated for all
patients with confirmed pituitary gigantism. The goals of treatment are to prevent the long-term consequences of GH
excess, remove the sellar mass, and preserve normal pituitary tissue and
function. Treatment options include surgery, targeted irradiation, and medical
therapy. Surgery transsphenoidal adenectomy by an experienced neurosurgeon—is
the treatment of choice and should be supplemented, if necessary, with Gamma knife radiotherapy, pharmacotherapy, or both.
