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U N I T 2
Integrative Body Functions
Pseudohypoparathyroidism is a rare familial disorder
characterized by target tissue resistance to PTH. It is
characterized by hypocalcemia, increased parathy-
roid function, and a variety of congenital defects in
the growth and development of the skeleton, includ-
ing short stature and short metacarpal and metatarsal
bones. There are variants of the disorder, with some per-
sons having the pseudohypoparathyroidism along with
the congenital defects and others having the congeni-
tal defects with normal calcium and phosphorus levels.
The manifestations of the disorder are due primarily to
chronic hypocalcemia.
Treatment.
The goals of therapy focus on the control of
symptoms while minimizing complications. Acute hypo-
parathyroid tetany, which usually occurs after surgery,
is treated with intravenous calcium gluconate followed
by oral administration of calcium salts and vitamin D.
Magnesium supplementation is used when the disorder
is caused by magnesium deficiency. Persons with chronic
hypoparathyroidism are treated with oral calcium and
vitamin D. Levels of serum calcium, phosphorus, and
creatinine (to check kidney function) are monitored at
regular intervals as a means of maintaining serum cal-
cium within a slightly low but asymptomatic range.
Hyperparathyroidism
Hyperparathyroidism is characterized by increased lev-
els of PTH. It can manifest as a primary disorder caused
by hyperplasia or tumors of the parathyroid glands, as
as a secondary disorder in persons with chronic kidney
disease or chronic malabsorption of calcium.
58–61
Manifestations.
Primary hyperparathyroidism is a
leading cause of hypercalcemia in the outpatient depart-
ment. It is seen more commonly after 50 years of age and
is more common in women than men.
58
Primary hyper-
parathyroidism causes an elevation in ionized serum cal-
cium and increased urinary excretion of both calcium
and phosphorus. The increased urinary concentration of
calcium and phosphorus may prompt the development
of kidney stones. Chronic bone resorption may produce
diffuse demineralization, pathologic fractures, and cys-
tic bone lesions.
Signs and symptoms of the disorder are related to
skeletal abnormalities, exposure of the kidney to high
calcium levels, and elevated serum calcium levels (see
hypercalcemia). At the present time, primary hyper-
parathyroidism usually manifests as an asymptomatic
disorder that is discovered in the course of routine bio-
chemical testing. Although thought to be asymptomatic,
these patents may experience nonspecific constitutional
symptoms such as fatigue, weakness, anorexia, and
bone pain.
60
Secondary hyperparathyroidism involves hyperplasia
of the parathyroid glands and occurs primarily in per-
sons with chronic kidney disease.
59,60
In the early stages
of chronic kidney disease, an increase in PTH results
from decreased serum calcium and activated vitamin D
levels. As the disease progresses, there is a decrease in
vitamin D and calcium receptors, making the parathyroid
glands more resistant to feedback regulation by serum
calcium and vitamin D levels. At this point, elevated
phosphorus levels induce hyperplasia of the parathyroid
glands independent of calcium and vitamin D levels.
The bone disease seen in persons with secondary hyper-
parathyroidism due to chronic kidney disease is known
as
renal osteodystrophy
(see Chapter 26).
Treatment.
Treatment of hyperparathyroidism includes
resolving the hypercalcemia with increased fluid intake.
Whenever possible, the underlying cause of secondary
hyperparathyroidismshouldbe treated. Parathyroidectomy
may be indicated in persons with symptomatic primary
hyperparathyroidism. The goal of medical management is
to normalize calcium levels. Calcitriol and other vitamin
D analogs may be used to control parathyroid hyperpla-
sia in chronic kidney disease. Persons with chronic kid-
ney disease may also need phosphate binders to decrease
intestinal absorption of phosphorus and prevent the skel-
etal disorders associated with the osteodystrophies (see
Chapter 26). Calcimimetic agents, which act through the
calcium-sensing receptor in the parathyroid gland, may be
used to decrease PTH production in primary and second-
ary hyperparathyroidism.
59–61
SUMMARY CONCEPTS
■■
Calcium, phosphorus, and magnesium are the
major divalent ions in the body.These divalent
ions are directly or indirectly regulated by a
number of factors including vitamin D and PTH.
■■
Calcium is a major divalent cation with
approximately 99% located in bone and less than
1% in the ECF compartment. Of the three forms of
ECF calcium, only the ionized form can cross the
cell membrane, contributing to neuromuscular
function, blood clotting, and enzyme reactions. In
hypocalcemia, decreased levels in ionized calcium
produce an increase in neuromuscular excitability;
and in hypercalcemia increased levels of ionized
calcium produce a decrease in excitability.
■■
Phosphorus is largely an ICF anion, being
incorporated into nucleic acids, adenosine
triphosphate (ATP), and 2,3-diphosphoglycerate
in the red blood cells. Hypophosphatemia,
which is associated with decreased intestinal
absorption, transcompartmental shifts, and
disorders of renal elimination, causes signs
and symptoms of neural dysfunction, disturbed
musculoskeletal function, and hematologic
disorders. Hyperphosphatemia, which occurs
with renal failure and PTH deficit, is associated
with decreased plasma calcium levels.
