Encyclopedia of Health and Medicine

154 The Endocrine System
of vitamin D, increases the amounts of calcium
the KIDNEYS retain and the intestines absorb, and
increases the amount of phosphorus the kidneys
excrete in the URINE.
Long-term excessive parathyroid hormone
secretion (HYPERPARATHYROIDISM) leads to OSTEO-
POROSIS, a condition in which there is substantial
loss of BONE DENSITY and STRENGTH. Inadequate
parathyroid hormone secretion (HYPOPARATHY-
ROIDISM) results in disruptions of NERVE impulses
and can cause muscle rigidity or cramping.
See also BONE; HYPERCALCEMIA; HYPOCALCEMIA.
pheochromocytoma A neuroendocrine tumor
that secretes DOPAMINE, EPINEPHRINE, and NOREPI-
NEPHRINE (collectively called catecholamines).
About 90 percent of pheochromocytomas are
noncancerous. Most pheochromocytomas develop
in the adrenal medulla, the inner structure of the
ADRENAL GLANDS, though can occur in other tissues
throughout the body. About 10 percent of
pheochromocytomas occur in conjunction with
MULTIPLE ENDOCRINE NEOPLASIA (MEN), an inherited
genetic disorder in which tumors form in numerous
endocrine structures. The primary consequence
of pheochromocytoma is HYPERTENSION
(high BLOOD PRESSURE), which results from the
excessive secretion of catecholamines. RETINOPATHY
(damage to the RETINA and OPTIC NERVE in the EYE)
and CARDIOMYOPATHY (enlarged and weakened
HEART) may result with long-term untreated
pheochromocytoma.
Symptoms and Diagnostic Path
Symptoms, aside from hypertension, often resemble
those of other endocrine disorders, notably
HYPERTHYROIDISM. Symptoms of pheochromocytoma
may include
• rapid, irregular PULSE (TACHYCARDIA)
• rapid breathing (tachypnea) or shortness of
breath (DYSPNEA)
• PALPITATIONS and ARRHYTHMIA (irregularities in
the heartbeat)
• orthostatic HYPOTENSION (a sudden drop in blood
pressure when rising from a seated or prone
position)
• HEADACHE, often severe and persistent
• bouts of NAUSEA and VOMITING
• anxiety and inability to concentrate
The diagnostic path includes blood tests to
assess blood electrolyte levels and to rule out more
common causes of the symptoms such as hyperthyroidism,
ELECTROCARDIOGRAM (ECG) to assess the
HEART’s electrical activity, and URINE tests to measure
the amounts of catecholamine metabolites
excreted in the urine. The endocrinologist may
also conduct diagnostic imaging procedures such
as MAGNETIC RESONANCE IMAGING (MRI) to detect the
presence and location of the pheochromocytoma.
Treatment Options and Outlook
Surgery to remove the pheochromocytoma is
nearly always the treatment of choice, as nonsurgical
therapies are not very successful in controlling
the tumor’s activities. Adrenergic blocker
medications (alpha blockers and beta blockers)
can relieve many of the symptoms. Hypotension
(low blood pressure) following the tumor’s
removal is common, with blood pressure gradually
returning to normal as the body’s production
of catecholamines returns to normal. CHEMOTHER-
APY follows surgery when the tumor is cancerous.
Most people recover fully and without complications
after surgery for noncancerous pheochromocytoma,
though tumors may recur in people who
have MEN. Recovery from malignant pheochromocytoma
depends on the extent of METASTASIS.
Risk Factors and Preventive Measures
People who have MEN have significant risk for
pheochromocytoma and should be alert to its
symptoms. There are no measures to prevent
these tumors from developing.
See also ADRENAL INSUFFICIENCY; MEDICATIONS TO
TREAT CARDIOVASCULAR DISEASE; SURGERY BENEFIT AND
RISK ASSESSMENT.
pineal gland A small ENDOCRINE GLAND, about a
quarter of an inch long, located within the BRAIN
very near the HYPOTHALAMUS. The pineal gland is
somewhat cone shaped and reddish in color. It
produces MELATONIN, a peptide HORMONE that regulates
the body’s circadian (sleep–wake) cycle.