Acromegaly and gigantism

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Acromegaly and gigantism

Definition

Acromegaly is a disorder in which the abnormal
release of a particular chemical from the pituitary gland
in the brain causes increased growth in bone and soft tis-
sue, as well as a variety of other disturbances throughout
the body. This chemical released from the pituitary gland
is called growth hormone (GH). The body’s ability to
process and use nutrients like fats and sugars is also
altered. In children whose bony growth plates have not
closed, the chemical changes of acromegaly result in
exceptional growth of long bones. This variant is called
gigantism, with the additional bone growth causing
unusual height. When the abnormality occurs after bone
growth stops, the disorder is called acromegaly.
Description
Acromegaly is a relatively rare disorder, occurring in
approximately 50 out of every one million people (50/
1,000,000). Both men and women are affected. Because
the symptoms of acromegaly occur so gradually, diagno-
sis is often delayed. The majority of patients are not
identified until they are middle aged.
Causes and symptoms
The pituitary is a small gland located at the base of
the brain. A gland is a collection of cells that releases
certain chemicals, or hormones, which are important to
the functioning of other organs or body systems. The
pituitary hormones travel throughout the body and are
involved in a large number of activities, including the
regulation of growth and reproductive functions. The
cause of acromegaly can be traced to the pituitary’s pro-
duction of GH.
Under normal conditions, the pituitary receives input
from another brain structure, the hypothalamus, located
at the base of the brain. This input from the hypothala-
mus regulates the pituitary’s release of hormones. For
example, the hypothalamus produces growth hormone-
releasing hormone (GHRH), which directs the pituitary
to release GH. Input from the hypothalamus should also
direct the pituitary to stop releasing hormones.
In acromegaly, the pituitary continues to release GH
and ignores signals from the hypothalamus. In the liver,
GH causes production of a hormone called insulin-like
growth factor 1 (IGF-1), which is responsible for growth
throughout the body. When the pituitary refuses to stop
producing GH, the levels of IGF-1 also reach abnormal
peaks. Bones, soft tissue, and organs throughout the body
begin to enlarge, and the body changes its ability to
process and use nutrients like sugars and fats.
In acromegaly, an individual’s hands and feet begin
to grow, becoming thick and doughy. The jaw line, nose,
and forehead also grow, and facial features are described
as “coarsening”. The tongue grows larger, and because
the jaw is larger, the teeth become more widely spaced.
Due to swelling within the structures of the throat and
sinuses, the voice becomes deeper and sounds more hol-
low, and patients may develop loud snoring. Various hor-
monal changes cause symptoms such as:
• heavy sweating
• oily skin
• increased coarse body hair
• improper processing of sugars in the diet (and some-
times actual diabetes)
• high blood pressure
• increased calcium in the urine (sometimes leading to
kidney stones)
• increased risk of gallstones; and
• swelling of the thyroid gland
People with acromegaly have more skin tags, or out-
growths of tissue, than normal. This increase in skin tags
is also associated with the development of growths,
called polyps, within the large intestine that may eventu-
ally become cancerous. Patients with acromegaly often
suffer from headaches and arthritis. The various
swellings and enlargements throughout the body may
press on nerves, causing sensations of local tingling or
burning, and sometimes result in muscle weakness.
The most common cause of this disorder (in 90% of
patients) is the development of a noncancerous tumor with-
in the pituitary, called a pituitary adenoma. These tumors
are the source of the abnormal release of GH. As these
tumors grow, they may press on nearby structures within the
brain, causing headaches and changes in vision. As the ade-
noma grows, it may disrupt other pituitary tissue, interfering
with the release of other hormones. These disruptions may
be responsible for changes in the menstrual cycle of
women, decreases in the sexual drive in men and women,
and the abnormal production of breast milk in women. In
rare cases, acromegaly is caused by the abnormal produc-
tion of GHRH, which leads to the increased production of
GH. Certain tumors in the pancreas, lungs, adrenal glands,
thyroid, and intestine produce GHRH, which in turn triggers
production of an abnormal quantity of GH.
Diagnosis
Because acromegaly produces slow changes over
time, diagnosis is often significantly delayed. In fact, the
characteristic coarsening of the facial features is often
not recognized by family members, friends, or long-time
family physicians. Often, the diagnosis is suspected by a
new physician who sees the patient for the first time and
is struck by the patient’s characteristic facial appearance.
Comparing old photographs from a number of different
time periods will often increase suspicion of the disease.
Because the quantity of GH produced varies widely
under normal conditions, demonstrating high levels of
GH in the blood is not sufficient to merit a diagnosis of
acromegaly. Instead, laboratory tests measuring an
increase of IGF-1 (3-10 times above the normal level) are
useful. These results, however, must be carefully inter-
preted because normal laboratory values for IGF-1 vary
when the patient is pregnant, undergoing puberty, elder-
ly, or severely malnourished. Normal patients will show a
decrease in GH production when given a large dose of
sugar (glucose). Patients with acromegaly will not show
this decrease, and will often show an increase in GH pro-
duction. Magnetic resonance imaging (MRI) is useful
for viewing the pituitary, and for identifying and locating
an adenoma. When no adenoma can be located, the search
for a GHRH-producing tumor in another location begins.
Treatment
The first step in treatment of acromegaly is removal of
all or part of the pituitary adenoma. Removal requires
surgery, usually performed by entering the skull through
the nose. While this surgery can cause rapid improvement
of many acromegaly symptoms, most patients will also
require additional treatment with medication. Bromocrip-
tine (Parlodel) is a medication that can be taken by mouth,
while octreotide (Sandostatin) must be injected every eight
hours. Both of these medications are helpful in reducing
GH production, but must often be taken for life and pro-
duce their own unique side effects. Some patients who can-
not undergo surgery are treated with radiation therapy to
the pituitary in an attempt to shrink the adenoma. Radiating
the pituitary may take up to 10 years, however, and may
also injure/destroy other normal parts of the pituitary.
Prognosis
Without treatment, patients with acromegaly will
most likely die early because of the disease’s effects on the
heart, lungs, brain, or due to the development of cancer in
the large intestine. With treatment, however, a patient with
acromegaly may be able to live a normal lifespan.