Page 333 - Problem-Based Feline Medicine

17 – THE CAT WITH WEIGHT LOSS AND A GOOD APPETITE 325

consistent with hyperadrenocorticism. False nega- dependent hyperadrenocorticism, but may be seen
tives and positives occur. in cats with PDH.
● Low-dose dexamethasone suppression test – ● Measurement of endogenous ACTH – Collect
Collect baseline blood sample, give dexamethasone blood sample in EDTA, spin immediately, transfer
0.01 mg/kg IV, collect blood after 4 and 8 hours. In plasma to a plastic tube, ship overnight on ice or
normal cats serum cortisol should be < 30 nmol/L freeze for storage. Plasma ACTH is high normal or
(< 1.0 μg/dl) at 4 h and 8 h after dexamethasone. above (>15 pg/ml) with PDH, and low (<10 pg/ml)
Lack of suppression is seen in most cats (95%) with with adrenal tumors.
hyperadrenocorticism, and some cats with non- ● Radiography, ultrasonography and, where avail-
adrenal illness. able, CT or MRI. Use to determine adrenal size
● Urine cortisol to creatinine ratio (UC/CR) – and shape. The presence of adrenal mineraliza-
Collect urine sample, centrifuge and submit super- tion should not be over-interpreted as it occurs in
natant. A normal ratio almost always rules out ~30% of normal cats. Unilateral adrenal enlarge-
hyperadrenocorticism. Unfortunately, an increased ment is typical of an adrenal tumor. While bilateral
ratio is commonly caused by non-adrenal illness. enlargement usually indicates PDH, it can occa-
The test is more reliable if the sample is collected at sionally result from bilateral adrenal tumors.
home. Hepatomegaly is found in ~75% of all cats with
hyperadrenocorticism. CT and MRI can be used to
Additional tests may be used to try to differentiate
image the pituitary gland as well as the adrenal
pituitary-dependent hyperadrenocorticism (PDH)
glands.
from adrenal neoplasia. These include:
● High-dose dexamethasone suppression test –
Performed as low-dose dexamethasone suppression Differential diagnoses
test but give 0.1 mg/kg. Lack of suppression at 8 h
Differential diagnoses include most of the other causes
is seen in most cats (80%) with hyperadrenocorti-
of weight loss with a good appetite. However, since
cism. Suppression at 4 h but not at 8 h is consistent
most cats with hyperadrenocorticism develop polyuria,
with PDH. False negatives may occur in mild cases
polydipsia and diabetes, other causes of diabetes,
of hyperadrenocorticism.
acromegaly, hyperthyroidism and renal insuffi-
● Ultra-high-dose dexamethasone suppression test –
ciency are the most important differentials.
Performed as low-dose dexamethasone suppression
test but give 1.0 mg/kg. Suppression at 4 h or 8 h to
< 30 nmol/l (< 1.0 μg/dl) or <50% of baseline is Treatment
consistent with PDH, but lack of suppression may
While there are a number of different treatment
be seen with PDH and adrenal tumors.
options, there have been few good studies into their use
● Combination test – Collect blood sample, give 1.0
in cats.
mg/kg dexamethasone IV, collect blood after 4 h,
then immediately perform ACTH stimulation test Medical therapies have generally given poor results,
as above. Interpretation is as for ACTH stimulation and safe dosages have not been established. They
test and ultra-high-dose dexamethasone suppres- may be given pre-surgically to reduce the operative
sion test (taking ultra-high-dose dexamethasone risks.
suppression test result as result at 4 h). ● Trilostane has produced promising results in a very
● ‘At home’ protocol – Collect urine on the morn- small number of cases and warrants further investi-
ing of Days 1 and 2; give two oral doses of dexam- gation, particularly given that side effects have not
ethasone at 8 hour intervals at 4 pm and 12 pm; been significant.
then collect a third urine sample on the morning of ● Mitotane gave poor results in early trials, and it has
Day 3. All three samples are assessed for UC/CR. been suggested that higher doses and/or longer
The mean of the first two UC/CR = basal value courses may be needed.
and acts as a screening test. Suppression < 50% ● Ketoconazole has given mixed results and consid-
basal on Day 3 is not seen in cats with adrenal- erable toxicity.