Page 251 - Problem-Based Feline Medicine

15 – THE CAT WITH POLYURIA AND POLYDIPSIA 243

Increased protein catabolism may also contribute to the ● The most frequent known causes are head
azotemia. trauma, neoplasia, hypothalamic-pituitary mal-
formations (e.g. cystic structures), or following sur-
See main reference on page 346 for details (The Thin,
gery to the hypothalamic-pituitary area.
Inappetant Cat).
● Rarely, central diabetes insipidus occurs in kittens,
suggesting a congenital form.
Differential diagnosis
Nephrogenic diabetes insipidus occurs when the
Renal failure and diabetes mellitus both cause weight renal tubules are unresponsive to vasopressin.
loss with PU/PD in aged cats. The PU/PD is more pro-
Unresponsiveness to vasopressin may result from prob-
nounced in diabetes and occurs with glycosuria. In
lems either at the receptor or with postreceptor mecha-
renal failure, appetite is usually reduced rather than
nisms, including inadequate hypertonicity of the renal
increased as in hyperthyroidism. The apathetic form of
medulla.
hyperthyroidism may be difficult to distinguish clini-
● Primary (familial) nephrogenic DI has not been
cally from renal failure but measurement of urea, crea-
reported in cats.
tinine and thyroxine usually distinguishes these
● Secondary (acquired) nephrogenic DI is com-
diseases.
mon.
– It occurs with renal failure, hyperthyroidism,
Treatment pyelonephritis, pyometra, hypercalcemia,
hypokalemia and drugs.
There are three treatment options: chronic administra-
tion of antithyroid drugs, surgical thyroidectomy,
radioactive iodine. See main reference on page 347 Clinical signs
for details (The Thin Inappetant Cat).
Polyuria and polydipsia occur ranging from mild to
severe, depending on cause, and is often present for
DIABETES INSIPIDUS* weeks to months.
Nocturia or urinary incontinence may result because
Classical signs
of the large volume of urine produced.
● Any age cat.
Weight loss may occur as a result of the underlying dis-
● Mild to marked polyuria and polydipsia,
ease, or when the water intake is huge.
often present for weeks to months.
● Nocturia or urinary incontinence may Neurologic signs may occur if DI is associated with a
occur. hypothalamic-pituitary neoplasia, e.g. stupor, disorien-
● Urine specific gravity is typically < 1.007, tation, ataxia, seizures, circling.
but in some dehydrated cats may be
1.007–1.020.
Diagnosis
Urine specific gravity is usually < 1.007, and often
Pathogenesis 1.001 or 1.002 in classical DI.
● Urine specific gravity may be 1.007–1.020 if the
Diabetes insipidus (DI) occurs in two forms, central
cat is very dehydrated, or has partial DI.
and nephrogenic.
● Partial DI frequently occurs with acquired nephro-
Central diabetes insipidus is very rare in cats, and genic DI such as renal failure, hypercalcemia,
occurs when vasopressin (antidiuretic hormone, ADH) hypokalemia, pyometra and pyelonephritis.
secretion from the hypothalamic-pituitary system is ● Urine, hematologic and serum biochemistry
inadequate. analyses must be performed to exclude causes of
● Central DI is most commonly idiopathic (i.e. no acquired nephrogenic DI. Renal failure, hyperthy-
cause identified on necropsy). roidism, pyelonephritis, pyometra, hypercalcemia,