Hyperparathyroidism in Cats: What it is and What to Expect

Key points

• Primary hyperparathyroidism is less common than secondary hyperparathyroidism.
• Hyperparathyroidism causes hypercalcemia (high calcium).
• Cats with hyperparathyroidism may have no symptoms at first.
• A veterinarian is needed for diagnosis.
• Primary hyperparathyroidism is often treated with surgery.

Common in

Middle-aged to older cats and Siamese cats (though still rare)

Symptoms & types

Hyperparathyroidism can be primary or secondary. Primary hyperparathyroidism is caused by a tumor or enlargement of the parathyroid gland — the gland is the cause of the disease. On the other hand, secondary hyperparathyroidism is usually associated with poor nutrition or kidney disease — the hyperparathyroidism is a result of another disease process.

If your cat has either primary or secondary hyperparathyroidism, you might notice some symptoms. However, not all cats with hyperparathyroidism will show any symptoms at all. Signs you might see include constipation, poor appetite, lethargy, and muscle tremors. You might also notice changes in your cat’s urination habits or see blood within their urine. As well as going off their food, your cat might also be excessively thirsty compared to normal. Occasionally, you or your veterinarian might feel a lump on the underside of your cat’s neck, where the parathyroid glands are located.

Symptoms of hyperparathyroidism in cats include: constipation, poor appetite, lethargy, muscle tremors, excessive thirst, excessive urination, bloody urine.

If your cat has hypercalcemia for a while without any treatment, it might cause calcium mineral deposits to form in the muscle or skin. One of the ways in which calcium becomes elevated is through the breakdown of calcium from the bones. Over time this can weaken the bones, and in extreme cases bones can fracture (break) as they are so weakened by this reduction in calcium.

Understanding the diagnostics

Hyperparathyroidism causes the body’s calcium levels to rise, so the first step in diagnosis is usually a blood test to look at calcium levels. If your cat hasn’t had any symptoms, the high calcium might just be picked up on a routine blood test. If calcium levels are high, this has to be confirmed with a more sensitive test at a specialist laboratory. Once confirmed, a similar blood test can be performed to check parathyroid levels. These specialist tests often require very specific amounts of blood products, with the samples being transported under chilled conditions.

Alongside calcium levels, initial blood tests might show an increase in the kidney parameters, including urea, creatinine, SDMA, and phosphate. This can be an indication of a knock-on effect of the calcium on the kidneys or could suggest that poor kidney function is the original cause of the hyperparathyroidism.

As well as blood tests, your veterinarian might recommend taking x-rays to check bone density and look for calcium deposits in the soft tissue or bladder. They might also suggest an ultrasound scan of the neck to look at the thyroid and parathyroid gland or perhaps performing a biopsy.

Learning about the causes

There are four parathyroid glands in the neck, located near the thyroid glands. They are responsible for regulating calcium and phosphate levels, which in turn maintain the bones. If more calcium is needed in the body, parathyroid hormone is released causing calcium to be released from the bones. Whereas if calcium levels are a bit high, it will be excreted in the urine and feces. 

In primary hyperparathyroidism, one or more of the parathyroid glands becomes enlarged. Usually, the enlargement is a benign growth, but occasionally it is a cancerous tumor. The enlarged gland becomes overactive, producing too much parathyroid hormone. This causes calcium to be released from the bone and levels to become high. Excess calcium gets deposited in soft tissue and can form stones within the bladder.

Hyperparathyroidism isn’t always caused by the gland itself though. Sometimes it’s caused by a severe nutritional imbalance or chronic kidney disease. Nutritional causes include too little calcium and Vitamin D in the diet, or too much phosphorous. Renal secondary hyperparathyroidism (caused by kidney failure) occurs when the kidneys are unable to excrete phosphate effectively. The rise in phosphorous alerts the parathyroid gland to make more parathyroid hormone, even though the calcium levels are high.

Cats who have too much parathyroid hormone will release calcium from their bones and absorb calcium from their guts, making their blood calcium levels too high.

Best treatment options

The best treatment for primary hyperparathyroidism is surgical removal of the affected parathyroid glands. However, it’s really important to give cats with hyperparathyroidism treatment to make them more stable ready for surgery. The main focus of stabilization treatment is to lower the calcium level, and this can be done with diuretics, certain steroids, and fluid via a drip. 

During surgery, the veterinarian will check each parathyroid gland and remove any that look enlarged or diseased. Surgery is usually very successful and leads to a cure, but cats often need to take Calcium and Vitamin D supplements for a while, as the sudden reduction in calcium can cause problems. Once the remaining glands get used to working harder, the supplements can be stopped.

Secondary causes of hyperparathyroidism can be treated by correcting the underlying cause and surgery is not required.

Home remedies and their effectiveness

Although it’s natural to want to try to make your pet feel better, sadly there are no home remedies that will fix hyperparathyroidism. However, it’s very important that you provide good home care to support your cat through their veterinary treatment. This includes keeping water freely available, tempting your cat to eat, and administering any medications that your veterinarian prescribes.

Surgery is the best treatment option as it is usually curative. Medication can be used to lower calcium levels, but these are not often used long term.

When to see a vet

If your cat seems lethargic, and is off their food, vomiting, or constipated, you’ll probably need to take them to see a veterinarian for a check-up. However, these signs are vague and do not necessarily mean that your cat has hyperparathyroidism. More specific signs of hyperparathyroidism include an increase in thirst and urination, blood in the urine, fractures, and calcium deposits in the skin. These symptoms are not exclusive to hyperparathyroidism either, but they are serious and should be investigated by your veterinarian as soon as possible.