In cats, aldosterone-secreting tumors represent the most identified adrenal tumor and are the most recognized cause of hyperaldosteronism. Another less well-defined syndrome of hyperaldosteronism in the cat involves bilateral micronodular hyperplasia of the zona glomerulosa of the adrenal cortex which has been associated with renal disease.

The predominant effects of mineralocorticoid excess are related to retention of sodium and water with increased renal excretion of potassium. These derangements lead to systemic arterial hypertension and potassium depletion. Hypertension is associated with retinal hemorrhage, loss of vision due to retinal detachment, and end-organ damage. Hypokalemia contributes to generalized muscle weakness and can be accompanied by altered gastrointestinal motility and skeletal weakness. When severe, hypokalemia may result in cervical ventroflexion, plantigrade stance, or even flaccid paralysis which can contribute to respiratory compromise.

Measurement of baseline aldosterone concentration (20002) is typically sufficient for identification of hyperaldosteronism. Serum or EDTA plasma can be submitted for analysis. In normal cats, the concentration of aldosterone in the body is directly influenced by the renin-angiotensin system and potassium concentration, and indirectly via adrenocorticotropic hormone (ACTH), natriuretic peptides and various neurotransmitters. The renin-angiotensin aldosterone system (RAAS) regulates blood volume, blood pressure, and sodium levels. The interpretation of the aldosterone result must consider the signalment, clinical presentation and additional laboratory test results, with emphasis on the status of electrolyte homeostasis (particularly sodium and potassium), blood pressure, and renal function. In cats with aldosterone-secreting adrenal tumors, baseline aldosterone concentrations are often greater than 1000 pmol/L.

Hyperadrenocorticism, or hypercortisolism, is an infrequent diagnosis in cats. In the majority of cases reported, feline hypercortisolism is associated with the presence of an adrenocorticotropic hormone (ACTH)-secreting tumor of the pituitary gland. The vast majority of these are benign adenomas. Excess adrenal stimulation by ACTH results in bilateral adrenal hyperplasia and excess cortisol secretion. Less frequently, cases of feline hypercortisolism are reported due to functional adrenocortical tumors autonomously secreting cortisol.

Hyperadrenocorticism is a disease of middle-aged to older cats. Clinical signs of hypercortisolism in cats are often nonspecific and may include weakness, abdominal distension, muscle atrophy and dermatologic signs including alopecia and fragile skin. Cats with concurrent diabetes mellitus often have polyuria, polydipsia, and polyphagia although these signs may reflect their diabetic state more than hypercortisolism. Weight loss, lethargy and gastrointestinal signs are possible but less commonly described.

The required sample for measurement of cortisol is serum. The low dose dexamethasone suppression test (LDDST) is the dynamic test of choice for diagnosis of hyperadrenocorticism in cats. It is important to note that the protocol for cats utilizes an intravenous dose of 0.1 mg/kg dexamethasone (higher than that used in the LDDST for dogs).

Once a diagnosis of hyperadrenocorticism has been confirmed, measurement of endogenous ACTH may provide additional insight if the origin of hyperadrenocorticism has not been elucidated by other diagnostics. Measurement for endogenous ACTH (20006) requires EDTA plasma. Please see special handling recommendations in the test catalog when preparing and shipping samples for endogenous ACTH. Cats with adrenal-dependent hyperadrenocorticism would be expected to have a low to undetectable concentration of endogenous ACTH.

Multiple hormone abnormalities have been identified in a subset of cats with adrenal tumors. Measurement of baseline progesterone (20037) or testosterone (20038) may be considered in some cases depending on the clinical presentation. Serum is the required sample type for measurement of progesterone and testosterone.

Primary hypoadrenocorticism is rare in cats. Clinical signs are variable, and a waxing and waning clinical course with partial response to supportive therapies may be noted.

The ACTH stimulation test is the dynamic test of choice for diagnosis of hypoadrenocorticism in cats. The required sample for measurement of cortisol is serum.

Cats with hypoadrenocorticism should have low baseline cortisol with lack of response to ACTH stimulation. If the patient has been receiving steroid therapy, concurrent measurement of baseline and post ACTH stimulation concentrations of aldosterone may be helpful. Identification of an increased concentration of endogenous ACTH in an untreated patient diagnosed with hypoadrenocorticism would support a diagnosis of primary hypoadrenocorticism. Measurement for endogenous ACTH (20006) requires EDTA plasma. Please see the special handling recommendations in the test catalog when preparing and shipping samples for endogenous ACTH.