Cat Health: Are Hyperthyroidism and Chronic Kidney Disease Connected?

A senior cat suffering from hyperthyroidism and kidney disease.

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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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.

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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


  • Lindsay D

    Our 5 year old cat had a tumor (which after removed was found to be benign) in his mouth toward the back and on the side of his tongue. Our vet said it was food allergies, so he got a steroid shot and has been only eating hypoallergenic food for 6 months. Now (only 1 month after seeing vet and no signs of tumors) we discovered he again has a large growth in his mouth near the back and on the opposite side of his tongue as the last time. Is this really a symptom of food allergies, could it be like the tumor related to hyperthyroidism? Any thoughts? I’m assuming this would be a pre existing condition, but is there a way to prevent because removal and all is over $1000. Is our vet misdiagnosing?

  • Dr. Jane Matheys

    Hi Lindsay-I’m sorry to hear that your cat is having problems. It’s difficult to address your concerns without knowing the exact diagnosis of the mass. I can say that oral tumors are not related to hyperthyroidism. It sounds like the tumor may be an inflammatory response to some underlying allergy other than a food allergy. If so, anti-inflammatory medications may be needed on a long-term basis to prevent recurrence. Discuss these possibilities with your veterianarian. Good luck with your cat’s treatment.

  • Evelyn Barrett

    I have a female cat about who is about16 months old. I got her when she was 4 months and she was not litter box trained; she wet my bed several days. I isolated her into a small room for approx. 3 months. She learned to use the litter box. Now she is dropping her feces on the rug in the cat room. I have 3 litter boxes and 2 cats. She started at the door area on the rug in the cat room, then stopped; she went on the wood floor behind the treadmill, now she is doing it on the rug. What can I do to get her to use the litter box? I keep the kitties out of my bedroom only.

    • Dr. Jane Matheys

      Hello Evelyn-The first place to start with your cat’s elimination problem is to have a thorough physical exam by your veterinarian to rule out any medical problems that could be causing the inappropriate defecation. If she checks out medically, then the doctor can help determine what behavior issues may be present. Make sure there are no hoods on the litter boxes, and do not use plastic liners. Cats do more “digging” when they defecate, so litter substrate is very important. Most cats like the softness of unscented clumping litter, but you may have to give her several litter options to “choose” from to see if she has preferences. Also try different locations of the litterboxes to see if she has a preference there, too. The general rule of thumb for number of litter boxes is number of cats plus one, so you’re good in that regards. Keep them scrupulously clean-scoop 2-3 times daily and dump the entire box monthlyand wash with soap and water only. If these suggestions do not correct the behavior, contact your veterinarian for further help before it becomes a chronic problem.

  • Sheila

    Hi – My cat has CKD and Hyperthyroidism. She just had the radio iodine therapy and was retested a couple days ago (1 month after treatment occurred). Her hyperthyroid increased unfortunately to T4-5.1, Creatinin:2.5mg. T3 (56), BUN (47), Ft4(pmol) decreased. Her Phospherous is 4.5. She’ll be retested again in a month but I’m trying to figure out what to feed her for her Kidneys. I heard K/D is ok (low protein and low phosherous) but based on research cats in early stage CKD should have a higher protein intake. Do you have any recommendations about which foods to feed her?



  • Dr. Jane Matheys

    Sheila-It’s not uncommon for cats to get a mild elevation in the BUN and creatinine after radioactive iodine therapy. Fortunately, it is generally mild, as in your cat’s case, and remains stable for a long time. Your cat has mild elevations of her BUN and creatinine, indicating she’s in the ealier stage of chronic kidney disease(CKD). You are correct that you don’t want to start restricting the proteins levels of her food too early or her body may start taking the necessary protein from her muscle tissue leading to muscle mass loss. If her potassium and phosphorus levels are normal, I recomend a quality high-protein, low-carbohydrate canned food to help increase the water flow through her kidneys. Then follow the progression of the CKD and make diet changes as needed.


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