Diabetes Insipidus in Cats

What is diabetes insipidus, and how is it different from diabetes mellitus?

There are two types of diabetes in cats: diabetes mellitus and diabetes insipidus.

Diabetes mellitus (DM) is also called sugar diabetes, and results from a disruption of pancreas function and abnormal regulation of blood sugar. The term “mellitus” means “sweetened with honey” in Latin; the name originated because the urine of these patients was “sweet,” due to high amounts of sugar excreted from the body. 

Diabetes insipidus (DI) is rare in cats, and is characterized by excessive thirst/drinking and the production of enormous volumes of extremely dilute urine. Some cats may produce so much urine that they become incontinent (incapable of controlling their urine outflow).

Despite drinking large volumes of water, the cat can become dehydrated from urinating so much. The term “insipidus” means “tasteless” in Latin; the name originated because the urine of these patients is diluted enough to be “tasteless” or “insipid”.

My cat is drinking and urinating a lot. Is DI the likely cause?

There are many causes of increased thirst (polydipsia) and increased urine production (polyuria), including diabetes insipidus, diabetes mellitus, liver problems, and kidney disease. It is essential that several diagnostic tests be performed to determine the cause of your cat’s problem.

What causes DI?

DI is caused by problems related to a hormone called vasopressin, also known as antidiuretic hormone (ADH), which is produced by the pituitary gland at the base of the brain. This hormone is essential for the kidneys to function properly.

The kidneys continually filter the blood and maintain the body’s water balance by excreting or reabsorbing fluid as required. To function properly, the kidneys require an adequate amount of ADH. This hormone causes the kidneys to keep more water in the blood, resulting in more concentrated urine.

Central diabetes insipidus (CDI) is caused by inadequate production of ADH. This condition may be due to a birth defect, brain trauma, intracranial tumor, a cyst or tumor in the pituitary gland, or no specific cause (idiopathic).

Nephrogenic diabetes insipidus (NDI) is caused by kidney resistance to ADH. This condition may be due to a birth defect, an adverse reaction to a medication, or secondary to certain diseases, including severe infection, metabolic disorders (e.g., hyperthyroidism), or advancing kidney disease.

How is DI diagnosed?

To diagnose DI, your veterinarian must first eliminate other potential explanations for increased drinking and increased urinating. Typical laboratory testing will include a complete blood count (CBC); a blood chemistry panel to evaluate blood sugar and liver and kidney parameters; a T4 (thyroid hormone) test; and a urinalysis. The urine concentration (specific gravity) is low in cats with DI.

A more advanced test, called the modified water deprivation test, can be used to diagnose DI, but must be performed under close veterinary supervision. This test is not commonly used because it can be difficult to get accurate results and involves some risk to the cat.

Your veterinarian may recommend a CT scan or MRI if there is any suspicion of a tumor in the pituitary gland. Your veterinarian may also recommend a trial treatment with medication to assess the cat’s response.

How is DI treated?

CDI is treated using a synthetic formulation of ADH called desmopressin (also known as DDAVP) that is applied as eye drops, nasal drops, or by injection under the skin. If a cat with CDI can have an unlimited water supply and ready access to litter boxes, treatment may not be required. Cats can still live a relatively healthy life without treatment. However, if water is restricted, they can quickly become dehydrated and ill.

NDI is treated using oral hydrochlorothiazide (a drug that can help reduce urine volume) and a low-salt diet. The underlying disease leading to NDI should be determined to provide more specific treatment.

Can DI be cured?

DI cannot be cured, except in the rare patient whose condition is caused by trauma, or in NDI patients where the underlying cause can be resolved; however, it can usually be successfully controlled. Without treatment, NDI results in dehydration leading to stupor, coma, and death.