Conn's Syndrome (Feline Hyperaldosteronism) 

©American Association of Feline Practitioners. http://www.aafponline.org/past_ce_bigsky.htm#Conn's Syndrome: Hyperaldosteronism

Classical signs associated with Conn's syndrome are weakness (due to hypokalemia), cervical ventroflexion, inappetence, weight loss, polyuria and polydipsia and onset of blindness (due to hypertension).

Conn’s syndrome is a rare condition in the cat and is caused by a unilateral neoplasm of the adrenal cortex that produces excess mineralocorticoids. Cats present with systemic hypertension, muscle weakness from hypokalemia, and polyuria. Aldosterone-secreting adrenal tumours causing primary hyperaldosteronism (Conn's Syndrome) are rare in the cat. Excessive secretion of aldosterone causes sodium retention and potassium depletion. The classic clinical manifestations of primary hyperaldosteronism are lethargy, weakness, mild hypernatremia, severe hypokalemia (usually < 3.0 mEq/L), and systemic hypertension. The contra lateral adrenal gland should be normal in size and shape on abdominal ultrasound. Documenting increased plasma aldosterone concentrations prior to and after ACTH administration is used to confirm the diagnosis. Treatment is removal of the adrenal tumour.

Clinical signs

Affected cats are typically old, ranging from 10-20 years. Clinical signs are mainly of hypokalemia including muscle weakness, ventroflexion of the neck, inappetence and weight loss, or of hypertension and include blindness from hypertensive retinopathy. Other signs include ataxia, abdominal enlargement and polyuria and/or polydipsia with two of five reported feline cases also having diabetes mellitus.

Diagnosis

Serum creatinine kinase activity is increased reflecting hypokalemic myopathy. Urine specific gravity is usually dilute (>1.040).

A presumptive diagnosis is based on finding persistent hypokalemia despite supplementing with high doses of potassium and intractable hypertension in an elderly cat. The finding of an adrenal mass and increased aldosterone concentrations help confirm the diagnosis.

Differential diagnosis

Phaeochromocytoma (tumour of adrenal medulla which produces excessive amounts of adrenalin and noradrenalin) may also cause hypertension in an elderly cat and be associated with an adrenal mass.

Other causes of hypertension including renal disease and hyperthyroidism.

Treatment

1) Potassium gluconate solution, tablets or powders

2) Amlodipine (calcium channel blocker) given at 0.625 - 1.25 mg/cat PO q 24h.

3) Trilostane - has been used in humans, but not as yet in cats.

Long term resolution involves surgical removal of the tumour.