Hyperparathyroidism in Cats

The parathyroid glands are part of the endocrine system. In healthy cats, parathyroid glands secrete parathyroid hormone. This hormone is involved in regulating the uptake, release, and use of calcium in the body.

The role of parathyroid hormone (PTH) is to increase blood calcium concentrations. In healthy cats, as calcium levels in the body rise, secretion of PTH decreases. As long as PTH levels are elevated, the body will continue to release calcium from the bones into the bloodstream.

Hyperparathyroidism is a rare condition that occurs when the function of the parathyroid glands is abnormal. The affected parathyroid glands release an excessive quantity of parathyroid hormone. This in turn leads to secondary complications due to sustained high levels of calcium in the bloodstream. The onset of disease is usually gradual, but left untreated can develop into severe, life-threatening illness.

Hyperparathyroidism isn’t the only disease process that causes elevated calcium thus a thorough investigation is warranted as soon as symptoms are noted. Treatment is possible in many cases and prognosis depends on the underlying cause.

If PTH levels remain high, the body continues to release calcium from the bones into the bloodstream. Over time, this leads to demineralization (softening) of the bones and calcium toxicity in the tissues.

Hyperparathyroidism has both primary or secondary causes. Primary hyperparathyroidism (PHPT) is caused by a tumor in one of the glands.

Secondary hyperparathyroidism (SHPT) results from either kidney disease or dietary imbalances.

One of the kidney’s functions is to break down and eliminate parathyroid hormone (PTH). In cases where underlying kidney disease is occurring, this system may be disrupted and unable to perform normally, leading to elevated levels of parathyroid hormone.

Elevated levels of PTH also result from a diet that is deficient in calcium or excessive in phosphorus. Nutritional imbalances are more likely in home-made or heavily supplemented diets.

Cats may be asymptomatic in the early stages of the disease.

Symptoms arising from long-standing elevated levels of PTH primarily result from elevated blood calcium levels or calcium depletion from the bones.

Symptoms vary based on the underlying cause and severity of the disease.

Other potential symptoms include:

• Poor body condition
• Mass in the neck
• Facial swelling and deformities
• Hunched posture
• “Rubber Jaw”: caused by severe demineralization of the bones that can cause the jaw to be bendable

Initial diagnostics include blood work, urinalysis, and x-rays. Elevated calcium is the most consistent laboratory finding and is usually found on routine blood work. If HPT is suspected, a parathyroid hormone assay can be performed to detect elevated levels. Advanced imaging or sampling of the parathyroid gland may also be helpful. Surgical exploration and biopsy may be needed in some cases to make a definitive diagnosis.

Primary HPT can be surgically corrected by removing the abnormal gland, leaving the other parathyroid glands intact to restore normal calcium regulation. Nutritional secondary HPT can be corrected by feeding a properly balanced diet. Secondary renal HPT is impossible to correct and management is aimed at supportive care.

Duration of the condition depends on the underlying cause and if it can be corrected. Prognosis for primary HPT and nutritional secondary HPT is good while renal secondary HPT is generally poor.

Primary and renal secondary HPT cannot be prevented. Nutritional secondary HPT can be prevented by feeding a balanced diet.

Hyperparathyroidism is not contagious.

Hyperparathyroidism is rare in cats.

• Surgical removal of abnormal parathyroid gland
• Dietary management
• Supportive care