Page 255 - Problem-Based Feline Medicine

15 – THE CAT WITH POLYURIA AND POLYDIPSIA 247

and osteoclast-activating factors, which lead to bone Clinical signs
resorption.
Signs associated with hypercalcemia are com-
Hypoadrenocorticism is a very rare cause of hyper- pounded by signs of the underlying cause of hyper-
calcemia in cats (<2% of hypercalcemic cats). It is calcemia, such as malignancy, toxicity from
likely multifactorial, and in dogs is related to the sever- cholecalciferol-containing rodenticides and renal failure.
ity of hyperkalemia. Mechanisms include hyperpro-
In general there is no breed or gender predisposition,
teinemia from dehydration and increased renal
although Siamese appear predisposed to primary
resorption of calcium.
hyperparathyroidism.
Other rare associations with hypercalcemia include ● Cats with hypercalcemia have a wide range of ages
hyperthyroidism, diabetes mellitus, liver disease (1–19 years) reflecting the multitude of causes, but
(hepatic lipidosis, bilary fibrosis), and bone marrow mean age is 9 years old.
diseases (myelodysplasia, myelofibrosis). ● Renal, gastrointestinal or neuromuscular signs
occur, and in part may reflect the underlying cause.
Idiopathic hypercalcemia is common in cats, and has
been postulated to be associated with acidifying diets, Lethargy, anorexia and/or weight loss are typical of
which increase bone turnover of calcium, but hypercal- hypercalcemia, regardless of the cause.
cemia was not corrected by partial parathyroidectomy
Polyuria and polydipsia occur in up to 25% of cats
or a non-acidifying diet. Many features are similar to
with hypercalcemia, and may be associated with inap-
familial benign hypercalcemia reported in humans
propriate urination.
which is associated with a mutation in the calcium-
sensing receptor. Signs of lower urinary tract disease, including
dysuria and pollakiuria, occur in approximately 20%
Chronic over-supplementation with calcium in
of cats. In a high proportion of cats, this is associated
the diet increases the intestinal absorption of cal-
with calcium oxalate urolithiasis of the urinary blad-
cium. It also stimulates bone resorption and results
der. Renal, ureteral, urethral or urolithiasis may also
in hypercalcemia and dystrophic calcification.
occur.
Because the ability to excrete the increased filtered
load of calcium is impaired in cats with renal failure, Vomiting occurs in 20–30% of cats with hypercal-
older cats are more sensitive to excess supplementa- cemia, including cats with idiopathic hypercalcemia.
tion. Dietary over-supplementation is rarely seen
Constipation or diarrhea are infrequently reported.
because of the widespread use of balanced commer-
cial diets. Neuromuscular weakness evidenced as a reluctance to
jump, or unsteadiness with jumping is less common.
Sequalae to hypercalcemia include:
● Chronic renal failure. High levels of calcium are Shaking, tremors, seizures, stupor and coma have the
toxic to the renal tubular cells, mineralize renal potential to occur with extremely high calcium concen-
tissue and interfere with ADH action causing renal trations, and are reported in dogs with cholecalciferol
failure and polyuria/polydipsia. Hypercalcemia can toxicity. Cats tend to ingest less toxin and these signs
also lead to calcium oxalate urolithiasis of the kid- have not been reported.
ney, ureter, bladder or urethra and result in signs of
Cardiac arrhythmias may occur if serum calcium is
lower urinary tract disease (LUTD).
more than 4.5 mmol/L (18 mg/dL). Prolongation of PR
● Reduced excitability of smooth muscle results in
interval and shortening of QT interval may be evident
altered gastrointestinal function. Chronic vomiting
on ECG.
is a common sign of hypercalcemia.
● Depressed skeletal muscle contractility and Acute cholecalciferol toxicity is associated with
weakness, and altered cardiac contractility and lethargy, anorexia and polyuria/polydipsia within
arrhythmias occur with high calcium concentra- 24 h of ingestion. Vomiting may occur, but the hemateme-
tions. sis and bloody stool seen in dogs have not been reported.