Feline hyperaldosteronism: Recognition and diagnosis - Veterinary Medicine
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Feline hyperaldosteronism: Recognition and diagnosis
Have a cat presenting with hypertension? Hypokalemia? Here's why you should add this disorder to your differential diagnosis list.


VETERINARY MEDICINE


CLINICAL SIGNS AND PHYSICAL EXAMINATION AND CLINICOPATHOLOGIC FINDINGS

Feline hyperaldosteronism does not appear to have a sex or breed predilection, but affected cats are typically geriatric,4-6,10-13,16,17 with a single case report describing a 5-year-old cat.14

Clinical signs

Clinical signs are typically associated with potassium depletion and systemic arterial hypertension. Owners may report signs of episodic or acute muscle weakness including the inability to jump on and off surroundings, plantigrade stance of the hindlimbs, inability to raise the head (cervical ventroflexion), and lateral recumbency or collapse. Presenting complaints may also include concerns of sudden blindness, mydriasis, and hyphema.

Physical examination findings

The main physical examination abnormalities reported in cases of confirmed or suspected primary hyperaldosteronism include elevated arterial blood pressure; ocular signs consistent with hypertension such as tortuous retinal vessels and hemorrhage, retinal edema, and retinal detachment; and hypokalemic polymyopathy.4-6,10-12,14,16,18,19 Keep in mind that not all cats with hyperaldosteronism will present with classic signs associated with hypokalemia or hypertension and, in fact, could present with just one of these abnormalities or have a completely normal initial physical examination. Other reported findings that are less specific in nature include polyuria, polydipsia, enuresis, weight loss, palpable abdominal masses, polyphagia, and a heart murmur with or without an irregular cardiac rhythm.4-6,10-12,14,16,18,19

Clinicopathologic findings

Typical serum chemistry profile abnormalities in cats with hyperaldosteronism include moderate to severe hypokalemia and normal to mildly increased sodium concentrations. The water reabsorption that occurs secondary to sodium retention will dilute plasma sodium concentrations and is likely the reason that this electrolyte is rarely elevated.10-12,14,16,17 Serum creatine kinase concentrations are also usually markedly elevated in cats with hypokalemic polymyopathy.12 In one study of 13 cats with primary hyperaldosteronism, potassium concentration at presentation was a mean of 2.5 mEq/L (reference range = 4 to 5.5 mEq/L), sodium concentration ranged from 148 to 168 mEq/L (reference range = 140 to 160 mEq/L), severe elevations in creatine kinase were present with a mean of 6,837 IU/L (reference range = < 120 IU/L) and 12 of 13 were hypertensive (≥ 170 mm Hg).12

The effects of aldosterone also cause a markedly increased fractional excretion of potassium in the urine. Evidence of renal disease can also occur in cats with hyperaldosteronism including isosthenuria and elevated serum creatinine and blood urea nitrogen concentrations.6,10,12 Cats that are initially presented with normal renal function, or mild azotemia, may experience progression of renal disease since hyperaldosteronism may lead to glomerular sclerosis, tubular atrophy, hyaline arteriolar sclerosis, and interstitial fibrosis.6

INDICATIONS FOR DIAGNOSTIC INVESTIGATION


Table 1
Any cat presenting with clinical findings of systemic arterial hypertension, hypokalemia, or mild azotemia should be considered for further evaluation of potential primary hyperaldosteronism. A thorough history and physical examination, complete blood count, serum chemistry profile, total T4 measurement, urinalysis, and indirect blood pressure measurement performed according to the American College of Veterinary Internal Medicine consensus statement20 will help rule out most other causes of hypokalemia and hypertension (Tables 1 & 2).


Table 2
If, based on the initial clinical examination and laboratory findings, primary hyperaldosteronism is considered a differential diagnosis, screening for abnormal regulation of aldosterone should be performed. If regulation is considered abnormal, the investigation should ideally continue to include diagnostic imaging to help determine potential treatment courses for the individual patient.


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Source: VETERINARY MEDICINE,
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