Page 261 - Problem-Based Feline Medicine

15 – THE CAT WITH POLYURIA AND POLYDIPSIA 253

Mineralocorticoid (aldosterone) deficiency directly Polyuria and polydispia are reported in 30% of cats.
affects renal function and the body’s ionic and water
Partial adrenal deficiency is characterized by episodic,
homeostasis.
non-specific gastrointestinal signs and lethargy or
● Loss of aldosterone secretion results in impaired
depression, which occur particularly at times of stress-
renal conservation of sodium and chloride and
ful events (travel, boarding, surgery).
excretion of potassium, leading to hyponatremia,
hypochloremia and hyperkalemia. A waxing and waning course of illness is typical.
● The loss of sodium and chloride reduces the extra-
A history of previous response to steroids or fluids is
cellular fluid volume, resulting in hypovolemia,
common.
hypotension, reduced cardiac output and decreased
renal perfusion.
● Hyperkalemia has deleterious effects on myocardial
electrical activity. Diagnosis
For clinical signs to develop there must be a loss of at Diagnosis is based on clinical signs plus a
least 85–90% of the adrenal cortices. sodium:potassium ratio of < 24:1.
Disease progression varies in severity depending on Definitive tests are an ACTH stimulation test com-
the degree of stress and the adrenocortical reserve. bined with measurement of ACTH concentration.
● Synthetic ACTH (Controsyn, Organon) adminis-
An Addisonian crisis is the most severe presentation
tered at 0.125 mg/cat IM with blood samples col-
of hypoadrenocorticism. This is the result of severe
lected at 0, 30 and 60 minutes or IV with samples
hyponatremia and hyperkalemia, which are the precur-
collected at 0, 60 and 90 minutes or ACTH gel (2.2
sors for hypovolemia, prerenal azotemia and cardiac
mg/kg) IM with samples at 0, 60 and 120 minutes.
arrhythmias.
● Cortisol concentration pre- and post-ACTH < 55
nmol/L (2 μg/dl) is diagnostic.
Clinical signs ● Elevated ACTH concentration differentiates spon-
taneous primary hypoadrenocorticism from iatro-
Very rare disease in cats.
genic steroid administration, because the cause of
Most common in young to middle age 1–9 years (aver- the spontaneous disease is lack of cortisol response
age, 6 years old). to ACTH.
In general, signs are similar to those in dogs. It often Hyponatremia occurs in cats, and is usually accompa-
presents with only vague clinical signs of lethargy, nied by hypochloremia.
anorexia and weight loss. Vomiting and diarrhea are
Hyperkalemia occurs in 90% of cats, but is less
less common signs in cats, as are changes in the elec-
marked (< 7.6 mmol/L or mEq/L) than in dogs.
trocardiogram associated with hyperkalemia.
Azotemia, hyperphosphatemia and dehydration
Signs may be present for only a few days or up to 4
occur in nearly all cats.
months prior to diagnosis.
Urine specific gravity < 1.030 was present in 70% of
Lethargy or depression are frequent signs.
cats.
Anorexia and weight loss are also common.
On physical examination, most cats (>50%) are dehy-
Differential diagnosis
drated, hypothermic or depressed.
Renal failure is much more common, and also typi-
Weakness, weak femoral pulses, and slow capillary
cally presents with azotemia and urine specific gravity
refill are common although, unlike dogs, collapse and
of < 1.030, and can have similar signs. The ACTH
bradycardia are rare.
stimulation test is normal in renal failure and the cats
Vomiting may be reported. tend to be older.