Optimal treatment of any persistent medical condition depends on establishing the correct diagnosis. The symptom group polyuria and polydipsia has many different potential causes, and it is important to identify the underlying cause before beginning treatment.
Diagnose and treat the cause
The cat owner may report increased thirst and urination. If the physical examination and baseline laboratory test results are normal, the owner can measure water intake at home for a few days to document the presence of polydipsia before pursuing further diagnostic tests. Polyuria and polydipsia usually do not constitute an emergency (hypercalcemia is an exception) but occasionally these symptoms arise from serious diseases that require prompt attention (e.g. diabetes mellitus). Hyperadrenocorticism
Specific diagnostic tests include adrenocorticotropin response test, low- and high-dose dexamethasone suppression tests, urine cortisol-to-creatinine ratio, abdominal ultrasound, and occasionally other specialized tests such as measurement of blood concentration of adrenocroticotropin, and elaborate imaging studies such as computerized tomography and magnetic resonance imaging.
Kidney insufficiency or failure
Diagnosis is based on serum biochemistry tests and urinalysis. Treatment is based on rehydrating the cat, trying to slow the progression of the kidney disease by dietary modification and treating complications such as hypertension and urinary tract infection.
Post-obstructive diuresis (polyuria that develops after relief of urinary obstruction)
This form of polyuria is transient but the cat must receive adequate fluid therapy to prevent dehydration during recovery.
This diagnosis is based on high blood glucose concentration and the presence of glucose, and often incompletely broken down fat products called ketones in the urine. Treatment depends on severity and may include hospitalization with intensive fluid and electrolyte therapy in conjunction with administration of short-acting insulin or outpatient management with long-acting insulin.
Diagnosis is based on measurement of serum thyroid hormone concentration and, in difficult cases, on specialized tests such as the T3 suppression test and radioisotope scanning of the thyroid gland with a substance called pertechnetate. If your veterinarian feels that a thyroid scan is required, your cat will be referred to a specialty clinic or teaching institution in your area. Treatment consists of surgery, radiation or drug therapy. Treatment with radioactive iodine ("I-131") will require referral to a speciality clinic or teaching institution in your area.
Treatment is based on correcting the underlying cause of potassium depletion. Causes may include: chronic loss of appetite; chronic muscle wasting; vomiting; diarrhea; administration of potassium-deficient fluids; potassium loss through the kidneys; alkalosis (high blood pH); administration of drugs that promote potassium loss; or some combination of these factors. Oral administration of potassium gluconate is the safest method of potassium supplementation.
High blood calcium concentration can be a medical emergency. Hypercalcemia often is a clue to underlying malignancy. Treatment with intravenous fluids, diuretics, and specific drugs may be recommended.
"Nephrogenic" diabetes insipidus
This disorder is a result of the kidney's inability to respond properly to anti-diuretic hormone, which normally facilitates water reabsorption in the kidney tubules. Usually this disorder is secondary to other problems (e.g. hypokalemia, hypercalcemia) but very rarely it can represent a congenital kidney defect (a problem present at birth). Treatment depends on the initiating cause, or symptomatic treatment may be necessary when no underlying disorder can be identified.
Central diabetes insipidus
This disorder is result of a deficiency of anti-diuretic hormone secretion from the pituitary gland at the base of the brain. It can be "idiopathic" (that is, of unknown cause), due to head trauma or due to a tumor in the pituitary gland. Water deprivation testing and response to anti-diuretic hormone administration confirm the diagnosis. A drug called DDAVP (a synthetic form of anti-diuretic hormone) is administered intra-nasally in drop form to treat central diabetes insipidus.
This disorder can be difficult to diagnose because identification of urinary tract infection by urine culture and sensitivity does not localize the infection to the kidneys. Diagnosis requires: integration of complete blood count results; urine culture and sensitivity results; contrast dye study of the kidney (so-called "intravenous pyelogram" or "excretory urogram"); ultrasound of the kidney; and possibly kidney biopsy. Treatment requires longterm administration of antibiotics.
Psychogenic polydipsia (compulsive water drinking)
This behavioral disorder is diagnosed on the basis of water deprivation testing after excluding other causes of polyuria and polydipsia. Most veterinarians perform gradual water deprivation to avoid confusion that can arise from loss of normal kidney concentrating ability that can arise simply as a result of longstanding polyuria (called "renal medullary washout" – discussed above). Treatment includes behavioral modification, gradual water restriction, and occasionally drugs to counteract obsessive-compulsive behavior.
Iatrogenic (i.e. "caused by treatment")
This cause of polyuria and polydipsia is managed by discontinuing the offending medical treatment.
Pyometra (uterine infection)
This disorder is diagnosed based on history (i.e. older intact female cat), complete blood count, and abdominal X-rays or ultrasound. Treatment involves surgery to remove the infected uterus or occasionally prostaglandin type drugs to evacuate the uterus if it is open and draining.
Diagnosed by serum biochemistry tests (including bile acids), abdominal ultrasound, and liver biopsy if necessary.
Definitive therapy of polyuria and polyuria depends on the underlying cause.