Page 241 - Problem-Based Feline Medicine

15 – THE CAT WITH POLYURIA AND POLYDIPSIA 233

● Hypercalcemia (p 245)
Associated with renal failure, lymphoma or squamous cell carcinoma, primary hyperparathy-
roidism, cholecalciferol rodenticide, infectious disease, diabetes mellitus, hyperthyroidism, liver
disease or idiopathic. Vomiting, weight loss, inappetence and in some cats, signs associated with
calcium oxolate urolithiasis (dysuria and inappropriate urination) may be present. In some cats,
signs are those of the primary disease process, e.g. renal failure or lymphoma.
PSYCHOLOGICAL
● Psychological polydipsia
This syndrome is not yet reported in cats.
INFLAMMATION INFECTIOUS (BACTERIAL)
● Pyelonephritis
Chronic form causes chronic renal failure with weight loss, inappetence. The acute phase may be
associated with fever, lethargy and pain on palpation of the kidneys. Bacteriuria, pyuria, casts
(especially WBC casts) may be present during the active infection, and occasionally leukocytosis
occurs.
● Cystic endometrial hyperplasia/pyometra complex (p 259)
Causes nephrogenic diabetes insipidus and PU/PD; vaginal discharge, inappetence, and weight
loss.
INFECTIOUS (IMMUNE)

● Chronic renal failure (glomerulonephritis or amyloidosis) (p 235)
Causes chronic renal failure and associated signs of PU/PD, weight loss, inappetence, lethargy, and
in the later stages, vomiting.
TREATMENT
● Drug induced* (p 244)
Drugs such as diuretics, phenobarbitol, amphotericin, gentamicin, thyroxine, corticosteroids, and
megestrol acetate may be associated with PU/PD through a number of mechanisms.

INTRODUCTION ● The solute load in the renal tubule is higher than
the capacity to reabsorb it, resulting in osmotic
diuresis. This is characterized by isotonic urine
MECHANISM?
with a SG 1.007–1.030. This occurs in the follow-
Polyuria and polydipsia in cats usually occurs ing circumstances:
because of a primary inability to concentrate urine. – Glomerular filtration of an absorbable solute in
This is referred to as primary polyuria and leads to excess of the renal tubular ability to reabsorb
compensatory polydipsia. Although not reported in it, e.g. glucose in diabetes mellitus. This may
cats, the kidney may also be overloaded with water also occur when the glomerular filtration rate
from primary polydipsia, termed psychogenic poly- (GFR) is reduced, as the increased solute load on
dipsia. Mechanisms for primary polyuria are as the remaining functioning nephrons may over-
follows: whelm their absorptive capacity.