thyroid gland provide permanent solutions to thy-
roid hormone overproduction. Most people subse-
quently require long-term thyroid hormone
supplements (HORMONE THERAPY) to maintain ade-
quate thyroid hormone levels in the blood, as
these treatments often leave the thyroid gland
incapable of synthesizing thyroid hormones. Total
thyroidectomy always requires thyroid hormone
replacement.
When the hyperthyroidism is likely transitory,
as with thyroiditis, treatment may target only
symptom relief because thyroid function will
return to normal when the inflammation subsides.
Beta blocker medications (notably propanolol)
relieve the symptoms that are the most distress-
ing—palpitations, irritability, and heat insensitiv-
ity. Endocrinologists also sometimes prescribe beta
blockers in conjunction with antithyroid therapies
when these symptoms cause pronounced discom-
fort, until thyroid function returns to normal.
A life-threatening complication of untreated
hyperthyroidism is THYROID STORM, in which there
are extensive cardiovascular and NERVOUS SYSTEM
responses to the elevated thyroid hormone levels.
Often, thyroid storm manifests in a person who is
unaware of having hyperthyroidism who develops
another health condition that stresses the body.
Congestive HEART FAILURE, serious arrhythmias, and
cardiovascular SHOCKcan develop very rapidly and
require emergency medical treatment.
Risk Factors and Preventive MeasuresExposure to radiation and excessive iodine con-
sumption are the primary known risk factors for
hyperthyroidism. People who have other AUTOIM-
MUNE DISORDERSare more likely to develop Graves’s
disease. The only preventable forms of hyperthy-
roidism are those which result from overcon-
sumption of thyroid-hormone supplements and
medication therapies that result in excessive
iodine consumption. Otherwise, there are no
known measures for preventing hyperthyroidism.
See also GRAVES’S OPHTHALMOPATHY; HYPOTHY-
ROIDISM.
hypoadrenocorticism See ADDISON’S DISEASE.
hypocalcemia A circumstance of insufficient
calcium in the BLOODcirculation. Common causes
of hypocalcemia include chronic DIARRHEA, which
prevents calcium absorption from dietary sources,
and lack of sun exposure, which prevents activa-
tion of vitamin D (crucial for calcium absorption).
HYPOPARATHYROIDISM is the most common
endocrine cause for hypocalcemia, and may result
from atrophy, dysfunction, or surgical removal of
the PARATHYROID GLANDS. Some people develop
resistance to PARATHYROID HORMONE, usually as a
consequence of vitamin D deficiency.
Calcium is essential for many functions within
the body, notably the conduction of NERVE
impulses and MUSCLEcontractions. Inadequate cal-
cium in the blood disrupts these functions and
may result in ARRHYTHMIA(irregular HEART RATE),
HYPOTENSION(low BLOOD PRESSURE), mental confu-
sion and irritability, and muscle spasms (tetany).
Severely low levels of calcium in the blood can
cause seizures, and prolonged hypocalcemia can
result in PAPILLEDEMA (swelling where the OPTIC
NERVEexits the RETINA) and permanent damage to
the CORNEA.
The diagnostic path includes blood tests to
measure the levels of calcium and parathyroid
hormone in the blood, a comprehensive NEURO-
LOGIC EXAMINATION, and an ELECTROCARDIOGRAM
(ECG) to assess any irregularities in the functioning
of the HEART. Other diagnostic procedures may
include X-rays of the bones, ULTRASOUND, COMPUTED
TOMOGRAPHY (CT) scan, or MAGNETIC RESONANCE
IMAGING(MRI) to visualize the parathyroid glands.
Treatment targets any underlying conditions, then
focuses on restoring appropriate calcium balance
in the body, typically through dietary changes to
increase the amount of calcium in the diet, and
with calcium and vitamin D supplements. Most
people recover fully and without residual conse-
quences with appropriate treatment. Long-term
treatment may be necessary, depending on the
cause of the hypocalcemia.
See also CHEMOTHERAPY; FANCONI’S SYNDROME;
PANCREATITIS;POLYGLANDULAR DEFICIENCY SYNDROME;
SEIZURE DISORDERS.hypoglycemia A circumstance in which the
BLOOD GLUCOSElevel is too low. A normal blood
glucose level is 70 milligrams per deciliter (ml/dL)
to 100 mg/dL. The clinical standard for hypo-
glycemia is a blood glucose level below 50 mg/dL,hypoglycemia 141