Low Production of Parathyroid Hormone in Cats

Hypoparathyroidism in Cats

An absolute or relative deficiency of parathyroid hormone in the blood, a condition called hypoparathyroidism, may be characterized by low levels of calcium in the blood, which can lead to hypocalcemia. The parathyroid hormone regulates calcium and phosphorus levels in the blood, normally increasing blood calcium levels by causing calcium to be reabsorbed from the bone.

The parathyroid glands are small, hormone-secreting glands that are located on or near the thyroid glands, which are in turn located at the front of the neck, in alignment with the larynx and trachea.

Mixed-breed cats are most commonly diagnosed, and it often appears secondary to surgical removal of the thyroid glands for treatment of excessive levels of thyroid hormone (known as hyperthyroidism). Less commonly diagnosed forms are due to parathyroiditis, and atrophy of the parathyroid glands. The average age of diagnosis is 12 to 13 years, with a range of 4 to 22 years of age. Spontaneous hypoparathyroidism occurs on average around two to three years of age, with an age range six months to seven years.

Symptoms

• Sluggishness (lethargy), lack of appetite, and depression
• Seizures
• Muscle trembling, twitching, or involuntary muscle contractions
• Panting
• Cataracts
• Slow heart rate (bradycardia)
• Fever
• Low body temperature (hypothermia)

Causes

This condition occurs most commonly in cats that have damaged parathyroid glands, or have had the parathyroid glands removed during surgical removal of the thyroid (thyroidectomy) in the course of being treated for excessive levels of thyroid hormone (hyperthyroidism). It may also occur due to a decrease in tissue of the parathyroid glands, usually of unknown cause. Immune-mediated inflammation of the parathyroid glands may also be seen.

Diagnosis

Your veterinarian will perform a thorough physical exam on your cat, taking into account the background history of symptoms that you are able to provide. Standard testing, including a complete blood profile will be conducted, as well as a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. The results of these tests will usually return normal in the case of hypoparathyroidism; however, they are important in discounting any other underlying disorders.

Because there are several possible causes for the symptoms described here, your veterinarian will most likely use differential diagnosis. This process is guided by deeper inspection of the apparent outward symptoms, ruling out each of the more common causes until the correct disorder is settled upon and can be treated appropriately. The main problems associated with hypoparathyroidism that must be differentiated from other disease processes are seizures, weakness, muscle trembling, and twitching.

Some of the causes that will need to be ruled out are heart related diseases, metabolic diseases, such as hypoglycemia (low blood sugar) or hepatoencephalopathy (liver disease that affects the brain's functioning). Neurological causes that will need to be ruled out are inflammatory diseases, tumors, or epilepsy.

An exploration of the cervical section of the throat may reveal that the parathyroid glands are absent or have atrophied (wasted).

Treatment

Your cat may need to be hospitalized initially for medical management of low levels of calcium in the blood, at least until the clinical signs are controlled. Other treatment will be dependent on whether any other underlying conditions have been diagnosed.

Emergency treatment is usually only needed for certain patients, such as those with primary hypoparathyroidism, or hypoparathyroidism that is secondary to procedures that have been used to correct excessive levels of thyroid hormone or excessive levels of parathyroid hormone -- that is, procedures that have been medically used to lower the amount of parathyroid hormone in the blood, and have resulted in levels of parathyroid hormone that are now too low.

If your cat has been diagnosed with hypocalcemia, low calcium levels in the blood, your doctor will prescribe long-term treatment for the condition. Vitamin D will be needed indefinitely, with the dosage amount determined by your veterinarian, based on your cat's needs. Calcium supplements can be given by mouth, again, with the type and dose of calcium supplement directed by your veterinarian.

If your cat is suffering from hypoparathyroidism related to a thyroidectomy, there is a good chance that they will recover normal functioning of the parathyroid glands within several months time.

Living and Management

Both low levels of calcium in the blood and excessive levels of calcium in the blood are concerns that will need to be managed over the long-term. Initially, your veterinarian will want to see your cat frequently in order to follow your cat's progress and to make changes to care as needed. Once serum calcium is stable and normal, your veterinarian will assess serum calcium concentration monthly for six months, and then every two to four months.