Page 256 - Problem-Based Feline Medicine

248 PART 4 CAT WITH URINARY TRACT SIGNS

Toxicity is less frequently reported and signs are less hyperphosphatemia, and a history of recent exposure
severe in cats than dogs. to rodenticide. Polyuria/polydipsia, vomiting and pain
Lower levels of cholecalciferol toxicity result in on palpation of the kidneys may also be present. PTH
PU/PD, inappetence and lethargy and low-grade and PTH-rP concentrations would be expected to be
vomiting, and clinically may be indistinguishable low if the cat is not dehydrated, but have not been
from acute or chronic renal failure. reported. Later there may be evidence of mineraliza-
tion of abdominal and other soft tissues. Toxicity
Physical examination findings are dependent on the
needs to be distinguished from other causes of hyper-
cause of hypercalcemia. Lymphadenopathy, abdomi-
calcemia and hyperphosphatemia (renal failure and
nal organomegaly or dyspnea may be evident in cats
hypoadrenocorticism) on the basis of history, signs
with lymphosarcoma. Cats with squamous cell carci-
and ionized calcium (often normal or decreased in
noma-associated hypercalcemia most often have
renal failure).
tumors of the head and neck. In contrast to dogs, a pal-
pable cervical mass is present in about 40% of cats with Chronic renal failure (renal secondary hyper-
primary hyperparathyroidism. parathyroidism) is associated with normal to elevated
PTH concentrations and low to undetectable PTH-rP
assay, hyperphosphatemia, but ionized serum calcium
Diagnosis
is usually normal or decreased. In contrast, ionized
Serum calcium concentration greater than 3 mmol/L serum calcium is increased with other causes of hyper-
(12 mg/dl). calcemia.
● The serum calcium concentration does not fluctuate
Idiopathic hypercalcemia is increasingly being identi-
with age in cats as it does in dogs, where a healthy
fied in cats (mean age 5 years). Typically cats are
puppy can have higher calcium and phosphorus lev-
hypercalcemic with normal or slightly low serum phos-
els.
phorus concentration, and have normal serum
A non-lipemic fasted blood sample is required for concentrations of PTH, calcitriol and 25-hydroxyc-
measurement of serum calcium, phosphorus, urea holecalciferol. Gross and histologic morphology of the
nitrogen and creatinine concentrations to differentiate parathyroid glands is normal. Subtotal parathyroidec-
between several of the causes of hypercalcemia. tomy does not resolve the hypercalcemia.
Hypercalcemia of malignancy is a relatively com-
mon cause of hypercalcemia in cats and is most often
Differential diagnosis
secondary to lymphoma and squamous cell carcinoma,
but may be from multiple myeloma or adenocarcinoma. Clinical signs of hypercalcemia (anorexia, lethargy,
Serum phosphorus concentration is below the midpoint vomiting, weight loss) are typical of many diseases,
of the reference range, unless renal failure is present. and serum biochemistry analysis is necessary to detect
Diagnosis of neoplasia-associated hypercalcemia is hypercalcemia.
based on documenting increased PTH-related protein
If PU/PD is present in addition to anorexia, vomiting
(PTH-rP) and suppressed PTH concentration in serum,
and weight loss, chronic renal failure would be the
or finding the primary tumor and demonstrating resolu-
most likely differential diagnosis based on clinical
tion of hypercalcemia with successful tumor therapy.
signs. Most cats with chronic renal failure are not
Primary hyperparathyroidism is rare in cats. It is hypercalcemic and of those that are, ionized calcium is
associated with anorexia and lethargy, an inappropri- usually normal or low.
ately high PTH concentration relative to the hypercal-
Chronic renal failure with secondary hypercalcemia
cemia. Serum phosphorus is below the midpoint of the
is usually differentiated from other causes of hyper-
reference range unless renal failure is present, and in
calcemia causing secondary renal failure by the pres-
some cats, a palpable cervical mass is evident.
ence of anemia, small kidney size on palpation or
Cholecalciferol poisoning is associated with acute ultrasound, and normal or low ionized calcium in
depression and anorexia, marked hypercalcemia and chronic renal failure. Cats with chronic renal failure