Psychogenic polydipsia(PP) is a syndrome resulting in a patient drinking inappropriately large amounts of fluid. In the case of dogs and cats their fluid intake is usually limited to water.
Poly is a Latin prefix meaning “many.” Dipsia is a Latin verb meaning “to drink.” Therefore, the polydipsic patient drinks often, or in large quantities, resulting in a 24-hour intake being higher than normal.
Of course, if intake is excessive, output, in the form of urine, will also be excessive, resulting in polyuria. Together they form a condition called polydipsia/polyuria, or pu/pd.
There is a very, very long list of medical abnormalities that can result in polydipsia. Diabetes mellitus,
Diabetes insipidus, Cushing’s Disease, renal failure, hyperthyroidism, liver disease, pyometra and many more.
Today, however, we are going to discuss a cause of pu/pd that is all in the patient’s head. As the name indicates, psychogenic polydipsia results from a thought process in a dog or cat’s psyche, or mind. Something stimulates the patient to want to drink and continue drinking instead of stopping when his thirst is satisfied. Such patients may be “excitable,” “wound too tightly,” or have a nervous personality.
In order for kidneys to work properly (in any species), the renal medulla (medulla is a Latin term meaning “middle”), which contains many structures, must have a solute gradient. To grossly oversimplify the solute gradient, think of a water bath with chemicals in a jar. The chemicals are least concentrated in the top of the jar, with concentration increasing toward the bottom. In order for the structures in the middle of the kidneys to work properly, they must be bathed in this mixture that is appropriately graduated.
In the patient with psychogenic polydipsia, the huge volume of water imbibed causes a constant effort to remove excess fluid from the body so that the bloodstream will stay in proper balance. As the kidneys work overtime to excrete the overabundance as urine, some of the solute in the solute gradient gets removed, too. As the exuberant drinking continues, eventually almost all of the solute is gone and the kidneys cease to have the ability to concentrate urine. This endpoint is called solute washout.
Fortunately, the kidneys know how to fix solute washout all on their own. However, there is an important step that we must perform: limit water intake. In a one-pet household, this is easy. Your pet’s doctor tells you a healthy amount of water for your pet to drink, and you ration it out through the day. Obviously, you can’t put out the entire day’s allowance of water first thing in the morning, or your dog will drink all of it at once, then be dehydrated for the remainder of the day. Allow a third in the morning, a third at lunchtime and the final third when you come home from work. If no one is home during the day you can provide two aliquots, but that’s not as good for your pet.
Alternatively, you might rig a timed pump for his water bowl, dispensing an hourly quantity of water.
Recovery from solute washout is not immediate, but the pet with psychogenic polydipsia will usually improve within a few weeks.
Options are limited if you have more than one pet. If you supply enough water for both, the PP dog will drink it all, leaving the other pet to dehydrate. If you put out an unlimited amount of water, the PP dog will be back to drinking excessively the first day.
Some clients manage. Muffie, pictured above, lives with three other dogs. She drinks, she urinates, and she maintains her housetraining despite the incredible volume of water intake and output. She thrives in spite of the potential for electrolyte imbalance, a tribute to our bodies’ amazing ability to tolerate abuse. Even laboratory testing shows no abnormalities, other than a very, very low specific gravity.
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See you tomorrow, Dr. Randolph.
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