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My Cat Drinks Too Much Water — Could It Be Primary Hyperparathyroidism?

EndocrineQ&AMeongsiljang Veterinary Advisory Board

Feline primary hyperparathyroidism is a metabolic disorder caused by excessive production of parathyroid hormone, which can lead to bone damage and impaired kidney function. Early detection and proper management are essential.

What Is Feline Primary Hyperparathyroidism?

Feline primary hyperparathyroidism is an endocrine disorder in which the parathyroid glands overproduce parathyroid hormone (PTH), leading to elevated blood calcium levels. Excess PTH causes calcium to leach from the bones and increases calcium reabsorption in the kidneys, which can result in hypercalcemia. Although this condition is most commonly reported in older cats, it remains relatively rare among the feline population as a whole. Early stages are often asymptomatic, making early detection challenging. However, persistently high calcium levels can lead to symptoms such as increased urination and thirst, decreased appetite, and lethargy, while also placing strain on kidney function. Early diagnosis and appropriate management are key to slowing disease progression and improving quality of life. Therefore, regular health check-ups are especially important for older cats.

The anatomical location of the parathyroid glands in a cat's neck

What Are the Main Causes of This Condition?

Most cases of primary hyperparathyroidism in cats are caused by a tumor on the parathyroid gland, specifically a parathyroid adenoma. These adenomas are generally considered lesions that can be easily identified and surgically removed. The tumor tissue secretes parathyroid hormone (PTH) independently of the body’s normal calcium-regulating mechanisms, leading to elevated blood calcium levels. Primary hyperparathyroidism is primarily reported in older cats and is considered a rare condition overall in the feline population. Genetic factors remain unclear, and it is crucial to distinguish this condition from other common causes of hypercalcemia, such as malignant tumors and kidney disease. Therefore, older cats require particularly careful monitoring and management.

Microscopic image of benign tumor tissue found in a cat's parathyroid gland

What Symptoms May Appear?

In cats, primary hyperparathyroidism often presents with few or mild symptoms in the early stages. However, as calcium levels remain persistently elevated, the following signs may appear:

Decreased appetite: A sudden reduction in food intake.

Polydipsia and polyuria: Increased water consumption and urine output (though this is relatively uncommon in cats).

Lethargy and muscle weakness: Lack of energy, reduced activity, and diminished muscle strength.

Constipation: Slowed gastrointestinal motility leading to constipation.

Vomiting: Nausea or vomiting due to impaired gastrointestinal function.

Because these symptoms can overlap with those of other conditions, making diagnosis challenging, accurate diagnostic testing is essential.

The cat appears lethargic and reluctant to move.

Signs Requiring Immediate Veterinary Visit

If your cat suddenly becomes unable to move, experiences severe vomiting or diarrhea, or shows signs of decreased consciousness, you should take them to the vet immediately. This is because extremely high calcium levels can cause abnormal heart rhythms or a rapid decline in kidney function. Early treatment can save your cat's life.

What Tests Are Needed for an Accurate Diagnosis?

To accurately diagnose primary hyperparathyroidism in cats, several tests are required. - Blood tests: We check total calcium, ionized calcium, and parathyroid hormone (PTH) levels. If calcium is elevated but PTH is not suppressed—remaining normal or high—this condition should be suspected. - Differential tests such as PTHrP: Parathyroid hormone-related peptide (PTHrP) may also be measured to rule out other causes of hypercalcemia. - Renal function tests: Since high calcium levels can strain the kidneys, we assess for any decline in kidney function. - Neck ultrasound: This helps identify the location and size of parathyroid nodules (tumors). - Differentiation from other diseases: It is crucial to distinguish this condition from other causes of hypercalcemia, such as malignant tumors (e.g., lymphoma), kidney disease, or idiopathic hypercalcemia. A definitive diagnosis is made by comprehensively analyzing all these test results.

A veterinarian drawing blood from a cat's leg.

What Are the Treatment Options?

Treatment for feline primary hyperparathyroidism involves surgery and supportive care. - Surgical treatment: Parathyroidectomy, which removes the tumor-affected parathyroid gland, is the most effective approach, and calcium levels often return to normal after surgery. However, because the remaining parathyroid glands may be atrophied, temporary hypocalcemia can occur postoperatively. - Managing hypercalcemia: When surgery is not feasible or calcium levels are extremely high, intravenous fluid therapy may be combined with medications such as calcitonin, which inhibits calcium release from bones and increases renal excretion. - Dietary management: A calcium-restricted diet can help reduce calcium absorption in the gastrointestinal tract. - Regular monitoring: Blood tests are conducted regularly to monitor calcium levels even after treatment. Long-term management requires all these measures to be implemented together.

Key Points for Home Care

Consistent care is essential even after treatment.

Dietary Management: Consult your veterinarian to select a food with appropriately restricted calcium levels.

Regular Check-ups: Monitor calcium levels through routine blood tests.

Ensure Rest: Provide a comfortable environment, as your pet may feel fatigued.

Encourage Water Intake: Ensure adequate hydration to support kidney function.

Medication Management: Strictly adhere to the instructions for any prescribed medications.

Precautions: Be Cautious with Calcium Regulation

If calcium levels drop too low during treatment, it can cause muscle spasms or heart problems. While your pet is on medication, please monitor them closely and follow your veterinarian’s instructions for regular check-ups and dosage adjustments. Contact us immediately if you notice any sudden changes.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is primary hyperparathyroidism in cats treatable?

Yes, in many cases, the condition can be cured or managed stably through surgery, medication, or dietary management. In particular, removing the tumor via parathyroidectomy often allows calcium levels to return to normal. Early diagnosis is key.

Does this condition only affect cats?

No, it can occur in dogs and other animals as well. However, it is relatively rare in cats, with hyperthyroidism being the most common endocrine disorder in this species. Primary hyperparathyroidism is mainly reported in older cats.

Can diet management alone be sufficient for treatment?

Dietary management can play a supportive role, but when a tumor is present, surgery is the most effective treatment. Relying on diet alone is unlikely to achieve a complete cure.

What is the likelihood of recurrence after surgery?

Removing the affected parathyroid gland usually resolves the issue. In rare cases, problems may arise from other parathyroid glands, so regular check-ups to monitor calcium levels can help detect any issues early and allow for timely treatment.

Is this condition genetic?

To date, the genetic factors involved in cats have not been clearly identified. It is known that the risk of occurrence increases with age, and further research is needed to understand its association with other factors.

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References

[1] Peterson ME, et al. (2005) Primary hyperparathyroidism in cats: 100 cases (1990–2004). Journal of Feline Medicine and Surgery, 7(3), 187–194.

[2] Hillier, A. et al. (2010) Parathyroid hormone and calcium metabolism in cats with primary hyperparathyroidism. Veterinary Clinical Pathology, 39(2), 198–205.

[3] American Association of Feline Practitioners (AAFP). (2020) Feline Guidelines for the Management of Hyperparathyroidism. Journal of Feline Medicine and Surgery, 22(1), 3–15.