Page 123 - Clinical Small Animal Internal Medicine

11 Hypoadrenocorticism in Dogs and Cats 91

related to hypersecretion of parathyroid hormone. was administered (0.05 mg/kg q12h) for four days, and
VetBooks.ir Hypercalcemia is also present in some of these cats. urine was collected to measure the urine aldosterone to
creatinine ratio (UACR) prior to the first dose, and the
Urine specific gravity is variable at the time of PHA diag-
nosis, ranging from 1.010 to 1.040 (mean 1.029).
Concurrent diseases reported in cats with PHA include morning after the last evening dose of fludrocortisone.
All of the non‐PHA cats had >50% suppression of the
hyperthyroidism, diabetes mellitus, and hyperprogester- UACR, while only 3/9 of the PHA cats had >50% sup-
onism. Thus, additional testing is prudent if a patient with pression of the pretest UACR. This test has its limita-
suspected PHA has clinical signs that cannot be explained. tions, including the availability of urine aldosterone
Since PHA caused by adrenocortical tumors and adre- measurement, but may be useful in PHA suspects with
nal hyperplasia has different treatment recommenda- PAC within reference range.
tions, abdominal and thoracic imaging is recommended.
Thoracic radiographs can help identify pulmonary Therapy
metastases. Abdominal ultrasonography (US), computed
tomography (CT), and magnetic resonance imaging Initial treatment of PHA is aimed at controlling hyper-
(MRI) can be used to visualize the adrenal glands and tension and hypokalemia and medical stabilization is
potential extension of a tumor into the caudal vena cava. recommended prior to adrenalectomy for adrenal
Reported ranges for unilateral adrenocortical tumors tumors. Spironolactone is a competitive aldosterone
range from 1–3.5 × 1–2.5 cm on US. The contralateral receptor antagonist that helps control both hyperten-
adrenal may not be seen, or may appear normal. CT and/ sion and hypokalemia. The starting dose is 2 mg/kg
or MRI is often used preoperatively to assess invasion of q12h but this dose may be increased to 4 mg/kg q12h.
the caudal vena cava. In cats with bilateral adrenal hyper- Spironolactone has been reported to cause facial der-
plasia, adrenal glands may be thickened, partially miner- matitis in Maine Coon cats treated for hypertrophic
alized, or normal upon US examination. Unfortunately, cardiomyopathy, but this has not been reported in cats
imaging is not always definitive. Pulmonary metastases with PHA. Amlodipine, a calcium channel blocker, is
and caval invasion may be missed, bilateral disease may given at 0.625–1.25 mg/cat q12–24h, to help control
be present when unilateral disease is suspected, and an hypertension. Potassium gluconate is administered at a
identified adrenal mass may be nonfunctional or produc- dose of 2–6 mEq PO q12h to alleviate hypokalemia.
ing something other than aldosterone, such as progester- While adjusting medication doses, blood pressure and
one, cortisol, or catecholamines. potassium concentration should be measured weekly.
The gold standard for diagnosis of PHA is the Myopathy is expected to resolve, although normoka-
aldosterone:plasma renin activity ratio, since aldoster- lemia may not be achieved. Hypertension usually
one concentration should be increased with concurrent resolves with appropriate therapy, but the vision loss is
decrease in plasma renin activity (PRA), resulting in an almost always permanent.
increased ratio. However, measurement of PRA is diffi- Patients with idiopathic adrenal hyperplasia should be
cult and inconsistently commercially available, limiting treated medically. Following medical stabilization, adre-
the utility of the ratio. nalectomy is ideal for patients with unilateral adrenocor-
The plasma aldosterone concentration (PAC) is the tical neoplasia. However, surgery is associated with a
most widely available test for confirmation of hyperaldo- high mortality rate (30% in one study), particularly if the
steronism. It is increased in all reported cases of PHA vena cava is affected. Additionally, some owners have
due to adrenocortical carcinomas or adenomas, but may financial limitations that prohibit surgery, and some cats
only be mildly increased or within reference range in have concurrent conditions or metastasis. If the owner
cats with adrenocortical hyperplasia. Additionally, an elects not to pursue surgical therapy, medical manage-
increased PAC does not differentiate between primary ment can be pursued long term.
and secondary hyperaldosteronism. Measurement of the The most common complication associated with
PAC:PRA ratio is useful in cases in which PAC is within adrenalectomy is hemorrhage; in one study, 4/10 cases
reference range, and when clinical information does not experienced intraoperative or perioperative hemor-
differentiate between primary and secondary hyperaldo- rhage. One patient was stabilized with autotransfusion
steronism (e.g., adrenal glands are of normal size and/or and another laparotomy, but the other three patients
azotemia is present). were euthanized following failed attempts at surgical
Adrenocorticotropic hormone stimulation testing is hemostasis.
not usually necessary for the diagnosis of PHA. However, Postsurgical monitoring includes blood pressure
suppression testing is used to diagnose PHA in people. and potassium monitoring, at least daily for 2–3 days.
In a small study in cats, an oral fludrocortisone suppres- Amlodipine and spironolactone are discontinued post-
sion test helped to differentiate some cases of PHA from operatively, and potassium supplementation is tapered
other causes of arterial hypertension. Fludrocortisone until the potassium concentration normalizes.