Cat Health: Are Hyperthyroidism and Chronic Kidney Disease Connected?

Dr. Jane Matheys, a veterinarian, guest blogs for pet insurance provider, Pets Best.

On the Pets Best Insurance Facebook page, Bonnie asked a question about cat health. She asks, “Are hyperthyroidism and chronic kidney disease linked in a causative manner, or are they just associated as many older cats develop both?”

Geriatric cats are prone to both hyperthyroidism and chronic kidney disease, so it’s not surprising that these conditions frequently coexist. The prevalence of concurrent kidney disease in cats with hyperthyroidism is estimated to be about 30-35%^{1, 2}. For a long time it has been unknown whether a true cause and effect relationship existed between the two, or if they are simply common in the geriatric feline independently. Recent research is slowly helping to make this less of a mystery, and it’s now known that thyroid function can definitely influence kidney function. Hyperthyroidism results from an overproduction of thyroid hormones from a tumor (usually benign) in the thyroid gland. An elevation in thyroid hormones increases the metabolic rate of the body which puts stress on all the major organs in the body. Previous studies have shown that hyperthyroidism can mask chronic kidney disease.

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Sign Up Now! Cardiac output can increase dramatically with hyperthyroidism. If kidney disease is already present, the increased blood flow to the kidneys helps them work better and improves their function. When the hyperthyroidism is treated, these effects are lost, which can result in the apparent worsening of the kidney function or development of kidney disease. It is important to remember that in these cases treating the hyperthyroidism does not cause the chronic kidney disease in these cats.  The kidney disease was already present before treatment but was masked by the effect of the hyperthyroidism on the cardiovascular system. Recent research provides evidence that untreated hyperthyroidism itself contributes to the development or progression of chronic kidney disease in cats. Studies suggest that hyperthyroidism can initially cause reversible kidney dysfunction which may become irreversible with time as chronic kidney disease progresses. Leaving a hyperthyroid cat untreated or poorly regulated with anti-thyroid medication may be detrimental to long-term kidney function. Treating and curing hyperthyroidism may help to both reverse kidney damage and preserve remaining kidney function. Curious about cat insurance? Pets Best Insurance can reimburse you off of your veterinary bills, from 70%-100% with no upper age limits on your cats. -- 1. Syme HM.  Cardiovascular and renal manifestations of hyperthyroidism.  Veterinary Clinics of North America: Small Animal Practice 2007;37:723-743. 2. Langston, CE, Reine NJ.  Hyperthyroidism and the Kidney.  Clinical Techniques in Small Animal Practice 2006; 21:17-21