Diabetes insipidus is a rare water regulation disorder in cats that is quite different from the more common diabetes mellitus. This condition occurs when a cat's body cannot properly regulate water balance. This results in the cat producing large amounts of dilute urine and experiencing excessive thirst.

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The most noticeable signs of diabetes insipidus typically develop gradually. You may notice that your cat is drinking much more water than usual - sometimes up to several times their normal intake. Along with increased thirst, cats will urinate much more frequently and in larger amounts. The urine appears very clear and dilute, almost like water, they may urinate in unusual locations - due to how often they need to urinate. Some cats do this due not wanting to use a wet litter box and therefore it can be worth placing multiple litter boxes around your home. Weight loss might occur despite a normal or even increased appetite. If left untreated, cats can become dehydrated despite drinking large amounts of water.

Diabetes insipidus occurs when the brain does not produce enough antidiuretic hormone, perhaps due to head trauma, brain tumors, or other brain injuries. Another type of diabetes insipidus is reported in dogs, when antidiuretic hormone is produced in normal quantity, but the kidneys do not respond appropriately to it (nephrogenic diabetes insipidus), but this has not been reported in cats. Sometimes, the cause of diabetes insipidus remains unknown, which veterinarians call "idiopathic diabetes insipidus".

Diagnosing this condition requires several steps. Your veterinarian will first take a detailed history of your cat's symptoms and perform a physical examination. It is likely they will do some tests on your cat’s urine and blood to rule out other conditions that can cause increased thirst and urination, such as diabetes mellitus, kidney disease, or hyperthyroidism. They may check your cat’s urine concentration and may also perform a test to check your cat's response to antidiuretic hormone. Sometimes, advanced imaging like MRI might be recommended to look for underlying causes, especially in cases of central diabetes insipidus. There is no specific test for diabetes insipidus and its diagnosis is made through exclusion of other causes and often response to treatment with hormone replacement.

For central diabetes insipidus, synthetic antidiuretic hormone replacement is usually prescribed, either as drops in the eyes, injections, or oral tablets. Depending on the cause of the diabetes insipidus then other treatments may also be required. Treatment is usually lifelong, but the success of treatment depends on what the cause is and if it involves managing a secondary condition such as a brain tumor.

The most important aspect of home care is ensuring your cat always has access to fresh, clean water. You will need to be prepared for increased litter box cleaning and might want to consider additional litter boxes around your home. Monitor your cat's water intake and urination patterns, keeping track of any changes. Regular veterinary check-ups are essential to adjust medication dosages and monitor your cat's overall health. Weight should be checked regularly, and any changes in drinking or urination patterns should be reported to your veterinarian.

Contact your veterinarian immediately if you notice any sudden changes in your cat's drinking or urination patterns, signs of dehydration (such as dry gums or loss of skin elasticity), significant changes in appetite or activity level, or if your cat seems unwell in any way. Regular monitoring is essential, and any concerns about medication side effects should be discussed with your veterinarian promptly. Early intervention can prevent complications and help maintain your cat's quality of life.