What is diabetes insipidus?
Diabetes insipidus (DI) gets its name from the fact that the urine of affected patients is dilute enough to be 'tasteless' or 'insipid'. 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).
The irony of this disease is that despite drinking large volumes of water, the cat can become dehydrated from urinating so much.
My cat is drinking and urinating a lot. Is diabetes insipidus 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, among others. It is essential that several diagnostic tests be performed to determine the cause of your cat's problem.
What causes diabetes insipidus?
Part of kidney function is to continually filter the blood that passes through them and to maintain the balance of the body's water by excreting or reabsorbing fluid as required. Efficient reabsorption requires an adequate level of a hormone called antidiuretic hormone (ADH), or vasopressin, which is produced by the pituitary gland at the base of the brain and causes the kidneys to keep more water in the blood, resulting in more concentrated urine. DI may be caused by inadequate production of ADH - this is called central diabetes insipidus (CDI), or by kidney resistance to the hormone - this is called nephrogenic diabetes insipidus (NDI).
Inadequate production of ADH, as in CDI, can be caused by a birth defect, brain trauma, intracranial tumor, a cyst or tumor in the pituitary gland, or there may be no specific cause found (idiopathic).
Lack of kidney response to ADH, as in NDI, can result from a birth defect, an adverse reaction to certain medications, or secondary to certain diseases, including severe infection, metabolic disorders (e.g., hyperthyroidism), or advancing kidney disease.
How is diabetes insipidus diagnosed?
Part of diagnosing DI involves first eliminating 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 liver and kidney parameters and blood sugar, T4 (thyroid hormone), and a urinalysis. The urine concentration (specific gravity) is quite low in cats with DI.
"Part of diagnosing DI involves first eliminating other potential explanations for increased drinking and increased urinating."
A more advanced test that can be used to diagnose DI is called the modified water deprivation test and must be performed under close veterinary supervision. This test is not commonly used because it can be difficult to get accurate results and is not without 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. Likewise, your veterinarian may recommend a trial treatment with medication to assess her response to this therapy.
How is diabetes insipidus treated?
The treatment for DI depends upon the definitive diagnosis. CDI is treated using a synthetic formulation of ADH, called desmopressin (DDAVP®), which is applied either as eye drops or by injection under the skin. NDI is treated using oral hydrochlorothiazide (HydroDiuril®) and a low-sodium diet. The underlying disease leading to NDI should be determined and addressed as well.
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.
Can diabetes insipidus be cured?
Diabetes insipidus 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.
