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 25-28 September, 2018 | Singapore
with HAC more commonly present with weight
loss, while weight gain is common in acromegaly. Alopecia is typically bilaterally symmetrical, may involve the thoracic, ventral abdominal, flank and limb regions and is patchy or generalized. Failure of hair regrowth after clipping is common. Secondary skin and nailbed infections are common as well
as opportunistic bacterial and fungal) infections including urinary, respiratory tract and oral cavity infections.
Haematology & Biochemistry
Changes on CBC are non-specific such as a stress leukogram and mild anaemia. On serum biochem- istry hyperglycaemia (85%), hypercholesterolaemia (35%), mild to moderate increases in ALT (30%) and/ or urea (30%) are the most frequent findings. Since cats have no glucocorticoid-induced isoenzyme of ALP, elevations of ALP (17%) only occur secondary to diabetes. Total thyroxine is normal or decreased (sick euthyroid syndrome). Cats with diabetes have glucosuria, and most maintain urine concentrating ability and have USG > 1.020.
Urine cortisol to creatinine ratio (UCCR)
Protocol: Two home-collected morning urine sam- ples on consecutive days. The UCCR has high sensitivity but low specificity for diagnosis of HAC in cats. It is used as a rule-out screening test due to the high predictive value of a negative result. UCCR results do not vary with age, gender, neuter status or breed, but hyperthyroid cats have significantly higher values.
Low dose dexamethasone suppression test (LDDST)
Protocol: 0.1 mg/kg dexamethasone EV, serum corti- sol measurements at 0, 4 and 8 h
In healthy animals, hypothalamic secretion of corticotropin-releasing hormone is suppressed for at least 24 h after dexamethasone administration, thereby suppressing pituitary ACTH secretion and adrenal cortisol secretion. Using this protocol, 4 and 8 h serum cortisol levels in healthy cats will be sup- pressed to <~40 nmol/L. Cats with HAC are resistant to pituitary suppression and have an 8 h cortisol above the reference range. Overall, the LDSST in cats has high sensitivity and moderate specificity
for the diagnosis. Cats with well or poorly controlled diabetes mellitus, without HAC, have comparable LDDST results to healthy cats.
Adrenocorticotropic (ACTH) stimulation test Protocol: 5μg/kg or 125μg/cat of co-syntropin
(synthetic ACTH) IV, serum cortisol measurements at 0 and 1 h. Healthy cats do not show cortisol level increases above the reference range. However, as few as one third of cats with HAC show positive test results. Thus, with its poor sensitivity and only mod- erate specificity, the ACTH stimulation test should not be used as an initial diagnostic screening test.
Discrimination between PDH and ADH
High dose dexamethasone suppression test (HDDST)
Protocol: 1mg/kg dexamethasone IV and serum cortisol measurements at 0, 4 and 8 h. Suppres- sion of >50% of baseline cortisol at 4 or 8 hours is suggestive of PDH but only occurs in approximately 40-50% of PDH cats.
UCCR with high dose oral dexamethasone sup- pression for diagnosis and discrimination Protocol: Home collection of two morning urine samples on consecutive days followed on day two by administration of 0.1 mg/kg oral dexamethasone at 8 am, 4 pm an midnight then collection of a third urine sample the next morning (day 3). If the UCCR of the first two urine samples (averaged) is within reference range then HAC is excluded, while an elevated result is consistent with HAC. Suppres- sion occurs if the UCCR of the third urine sample is <50% of baseline and this result is consistent with PDH. Less than 50% suppression means that differentiation between ADH and PDH cannot be determined7.
Endogenous ACTH measurement
Plasma endogenous ACTH levels are expected to be increased in cats with PDH and decreased in cats with ADH. Because endogenous ACTH values in affected cats may fall within the reference range, this test cannot be used as a screening test for HAC.
Diagnostic imaging
Protocol: Ultrasonography and bilateral measure- ments of adrenal length and height of cranial and caudal poles. Most cats with PDH have bilaterally symmetrical adrenal gland enlargement. However, in some adrenal size falls within reference ranges or adrenomegaly is unilateral. Adrenal calcification can be an incidental finding on abdominal radiographs in healthy cats. Cats with ADH have a unilateral adrenal mass or adrenomegaly. The uninvolved ad- renal is atrophied or may be of normal size. Bilateral adrenocortical adenomas and bilateral tumours of different functional type (e.g. phaeochromocytoma) occur occasionally. The adrenal glands of hyperthy-

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