The parathyroids are four small glands in the neck located near the thyroid
gland. The parathyroid glands secrete the hormone PTH, which is essential to
bone metabolism and blood calcium regulation. As the blood calcium level falls,
the parathyroid glands compensate by releasing more PTH, which raises the
calcium level in the blood by drawing calcium out of the bones. High serum
phosphorus levels will also stimulate the body to secrete PTH. Accordingly,
either a low serum calcium or a high serum phosphorus will cause an excess of
PTH in the blood. When this situation goes unchecked, the bones become
demineralized, thin, and often look cystic (small holes in the bone) on X-ray.
Minor stress can cause a fracture.
There are several conditions related to abnormal parathyroid gland
This is characterized by the passing of a blood clot (embolus) from the left
side of the heart into the general circulation, where it becomes lodged in an
artery. The resulting obstruction to the flow of blood leads to clotting of the
The most common site for blockage is the point at which the abdominal aorta
branches into the main arteries that supply the rear legs. Arteries elsewhere
in the body can be affected, particularly in the kidneys. Diagnosis of the rear
Low levels of parathyroid hormones are almost always associated with the
inadvertent removal of the parathyroid glands during surgery for hyperthyroidism. In this case,
cats have a low level of blood calcium and may have
Treatment: Treatment involves oral or even intravenous calcium
supplementation. Many cats adapt to this problem with time and medication, but
it can be serious immediately after the surgery.
This rare condition is due to a parathyroid gland tumor that produces excess hormone. These are usually
benign adenomas and are seen in older cats.
Treatment: Surgical removal of the affected gland is the only possible
Renal Secondary Hyperparathyroidism
This condition is the result of long-standing kidney disease that causes the
cat to retain phosphorus. The high serum phosphorus stimulates the parathyroid
glands to produce excessive amounts of PTH. Effects on the bones are the same
as those of nutritional secondary hyperparathyroidism (page 366). However,
signs of kidney failure are usually the
Treatment: Treatment is directed toward correcting the kidney disease.
Nutritional Secondary Hyperparathyroidism
The cause of this nutritional bone disease is a diet consisting primarily of
organ meats, such as hearts, livers, and kidneys. Such a diet is too high in
phosphorus and too low in calcium and vitamin D. (Vitamin D is necessary for
calcium to be absorbed from the small intestine.)
Kittens are at particular risk because they require large amounts of calcium
for growth and development. When a kitten’s sole source of nourishment is meat,
he’s getting too much phosphorus and not enough calcium. This results in
overactivity of the parathyroid glands.
Symptoms appear after the kitten has been on a high-meat diet for about four
weeks. Affected kittens are reluctant to move, and they develop an
uncoordinated gait and lameness in the back legs. The front legs are often
bowed. Their thin bones are easily fractured. These fractures, often multiple,
tend to heal rapidly and may even go unrecognized. Because the meat diet
supplies adequate calories, kittens often appear well-nourished and have a
healthy coat despite their metabolic bone disease.