By John Berg
A 9-year-old spayed female domestic short-haired cat presents with a two-week history of progressive lethargy.
The owners relate that she occasionally seems to have trouble rising and often seems to have difficulty raising her head. They also report that the cat sometimes seems slightly disoriented lately, and when you check her vision, she appears to be blind and has markedly dilated pupils. You obtain a CBC and chemistry profile.
When the bloodwork comes back the next day, the CBC is normal; however, the chemistry profile shows a potassium range of 2.4 with no other significant abnormalities. Suspecting that you know what the problem is, you call the owners and ask them to return for a blood pressure measurement. The result is 190 mmHg.
Question: What is the most likely diagnosis given the history, physical exam findings and bloodwork results, and blood pressure?
Answer: Hyperaldosteronism caused by an aldosterone-secreting adrenal tumor.
Question: What are the major functions of aldosterone?
Answer: The main function of aldosterone is to sustain extracellular fluid volume and blood pressure through renal reabsorption of sodium and excretion of potassium. If blood pressure falls, the kidneys sense this and release renin, which converts angiotensinogen to angiotensin I. Angiotensin-converting enzyme (ACE) produced in the lung capillaries converts angiotensin I to angiotensin II, which causes vasoconstriction, increasing blood pressure. Angiotensin II also stimulates the adrenal glands to produce aldosterone, which increases renal sodium reabsorption. Water follows, also increasing blood pressure.
Classic clinical signs in cats with hyperaldosteronism are lethargy and ventroflexion of the neck caused by muscular weakness secondary to hypokalemia. Marked elevation in blood pressure may result in retinal detachment and blindness.
Question: What is the preferred treatment for aldosterone-secreting tumors in cats?
Answer: Medical management with potassium supplementation, antihypertensive drugs such as amlodipine, and the aldosterone antagonist spironolactone can relieve clinical signs and give reasonable survival times. However, unless the cat is geriatric or has significant concurrent diseases, adrenalectomy is the preferred treatment because it eliminates clinical signs and results in prolonged survival times (median of 1297 days in one report). The risk of surgery is increased substantially if ultrasound or CT show tumor invasion into the vena cava. A finding of bilateral adrenal masses also increases surgical risk. Fortunately, most cats have benign tumors or malignant tumors with low metastatic potential.
Dr. John Berg is a professor of soft-tissue surgery at Cummings School of Veterinary Medicine at Tufts University. He is a diplomate of the American College of Veterinary Surgeons and an honorary member of the Society of Veterinary Surgical Oncology. He also serves as editor-in-chief of the Tufts newsletters Catnip and Your Dog.