by Perry McCarney

Created on: January 16, 2009   Last Updated: December 25, 2009

Our cats are susceptible to two varieties of feline diabetes. Diabetes insipidus is quite rare but can occur in any cat of any age. The far more common diabetes mellitus is similar to human diabetes mellitus type II. It is therefore most common in middle-aged to older cats, with an increased likelihood in overweight cats, particularly those that are excessively overweight or obese. It's thought that toms may be more prone to diabetes mellitus than queens.

Diabetes Insipidus

Central or hypophyseal diabetes insipidus (CDI) is due to the reduced manufacture of antidiuretic hormone (ADH) caused by damage to the hypothalamus, which is located below the brain. The damage may be caused by a neoplasm (cancer), cysts, an inflammatory granuloma (clump of monocyte or macrophage white blood cells) possibly resulting from an infection, or internal hemorrhaging (bleeding) resulting from a head trauma (injury).

Nephrogenic diabetes insipidus (NDI) results from the tubules (small tubes) in the kidneys failing to respond appropriately to normal and increasing levels of ADH in the blood. NDI may result from a blockage in the urinary tract, high calcium or low potassium levels in the blood, or from the use of some drugs, such as amphotericin B, which is an antifungal agent that is sometimes used to treat infections of yeast or fungi.

ADH is the hormone that controls the reabsorbtion of water by the kidneys during the blood filtering process that results in urine. If the cat's blood pressure is high, ADH production reduces so that more water is left in the urine, thus reducing blood volume and pressure. If it's low, more ADH is produced increasing the amount of water reabsorbed and at the same time the cat experiences thirst, so it will drink more and increase blood volume and thus pressure that way as well.

So the primary clinical sign for either type of diabetes insipidus is polyuria (increased urination) and this will occur whether the cat is drinking or not. The urine being produced will have a high water content, so will be quite pale, although getting to see this may be difficult. You might keep your cat enclosed in the bathroom with plenty of water until they are forced to urinate on the floor, thus letting you see the color. An injury to the hypothalamus may also short-circuit the thirst impulse, but if not or the cat has NDI it will also display polydipsia (an increased thirst). If the cat is not drinking, dehydration can occur very rapidly and quickly become life-threatening.

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