When your pet tanks up at the water bowl, is it really a problem? Or is it merely a response to a hot environment or a dry diet?
When excessive thirst or polydipsia is associated with the production of excessive amounts of urine or polyuria, we may safely assume that something is amiss. But the problem could be either behavioral or physical. And which comes first, increased thirst or increased urination? The problem, in fact, might be excessive urine production that drives greater thirst and water consumption.
The diagnostic approach to PU/PD (polyuria/polydipsia) may be simple and straightforward, but often it is not. The veterinarian must be certain that any changes in urination habits are caused by greater than normal urine output, rather than urgency and difficulty urinating or loss of bladder control. Verifying the problem, therefore, is extremely important.
After collecting a detailed history, the veterinarian may wish to observe the pet's urination, so that he or she can assess normalcy and completeness of emptying. The volume and quality of the urine produced is of paramount importance, since the urine's specific gravity directly reflects the concentration of the urine and, indirectly, the volume of urine produced. If the urine sample is very dilute, it will have a low specific gravity, indicating that excessive urine production is probable. However, if the pet produces urine that is particularly well-concentrated, then excessive urine production is not likely.
A urine specimen collected in a sterile fashion, especially by needle procedure or cystocentesis, is frequently used to complement the information provided by a voided specimen. The presence of abnormal cells or protein levels in the urine may suggest urinary infection as the cause of the change in urination habits, rather than too much urine.
Another important step in getting to the bottom of this problem is the owner's measurement of the patient's average daily water consumption. Most dogs and cats will consume 20 to 70ml/kg (1kg = 2.2 lbs) in a 24-hour period -- this figure takes into consideration both free water consumed and dietary water, which is higher in canned foods. Pet owners will be asked to measure carefully the pet's water consumption for three to four consecutive days, and present an average. This can be a challenging task if there are multiple animals sharing a bowl, or if the pet has access to a pool or pond. It is also important to make toilets and other fountains off limits during the test time.
Of course, if these tests reveal no evidence of elevated water intake or no suggestion of increased volume of urine produced, then the problem should be re-defined as something other than PU/PD.
Upon verifying that PU/PD is the problem, the veterinarian will need to determine whether it's thirst (polydipsia) or urination (polydipsia) is the primary problem. Primary polyuria is more common in dogs and cats, and is commonly associated with problems in the kidneys' urine concentrating mechanism. Diseases such as kidney failure, diabetes mellitus, hyperadrenocorticism (Cushing's Disease) and hyperthyroidism are commonly presented with these signs. Any history of medication use is reviewed, especially if corticosteroids or anticonvulsants have been recently prescribed, as these medications are likely to produce PU/PD.
The systemic balance between water intake and water output is controlled largely by the action of the antidiuretic hormone (ADH) on the kidneys. In kidney failure, the kidneys become less responsive to the normal hormonal effects of ADH and they are further challenged by excessive waste products in the bloodstream; both of these problems can contribute to primary polyuria. Certain systemic bacterial infections, especially those associated with uterine or kidney disease, may inhibit the action of ADH at the kidney, as may corticosteroid hormones, either produced naturally or given as medication. The end result is that the dog or cat urinates too much, and drinks excessive water to avoid becoming dehydrated.
Similarly, diabetic pets produce massive quantities of dilute urine because of the presence of sugar in the urine that drags water along with it. The diabetic pet drinks to keep up with the massive urine output. In all these pets, withholding water could be disastrous, because the high urine output would continue, leading to dehydration if water loss is not met by water intake.
Liver failure and low protein diets may each contribute to polyuria through secondary influences on the kidney's water-concentrating mechanisms. Diuretic medications such as furosemide or spironolactone are administered to alter the water balance of the body. Dogs or cats with congestive heart failure or fluid retention in the abdomen are treated routinely with diuretics to reduce the body's water load.
Less commonly, pets will have primary polydipsia, or excessive thirst. Hyperthyroidism is a very common problem in aging cats that is frequently associated with primary polydipsia. In the geriatric cat, increased thirst and urination can have multiple causes, including kidney failure, hyperthyroidism and possibly diabetes mellitus, as well. Successful treatment of hyperthyroidism may not, then, resolve PU/PD in affected cats -- in fact, it may permit the apparent worsening or unmasking of kidney failure when some of the stimulus to drink is removed.
Compulsive water consumption is occasionally driven by disruptions in the thirst center of the brain's hypothalamus, subsequent to trauma, tumor or inflammatory disease. Insufficient production of ADH in the hypothalamus, termed central diabetes insipidus, is another rare condition that causes PU/PD. Psychogenic polydipsia may be a behavioral phenomenon, especially in young, excitable large breed dogs, where no organic lesion is discovered. Dogs in pain or distress may be drinking excessively as well.
Eliminating the problem of PU/PD will require an understanding of its origin or cause. Some conditions are easier to tackle than others. Only after the veterinarian is able to confidently exclude all medical problems should water restriction be implemented. If patients are drinking to meet physiologic needs, withholding water can be life-threatening. Fortunately, polyuria and polydipsia rarely cause serious medical consequences provided patients are able to consume the quantities of water required and eliminate normally. This provides the owner and veterinarian time for an orderly approach to the problem of PU/PD, once it is verified and proves to be sustained. Your veterinarian remains your best resource to help sort out the puzzle of polyuria and polydipsia. With good luck and an orderly approach, he or she may be able to save your carpeting!
Written by Celeste Clements, DVM
Permission for use of article came from VetCentric.com