Beyond Feline Diabetes

Sometimes when I talk to other veterinary people, either doctors or nurses, I get the impression that they fall into one of two categories: people who love diagnosing and managing feline endocrine cases, and people who would rather undergo an invasive medical procedure.

Demystifying Common Feline Endocrinopathies

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Left untreated, cats suffering from hyperaldosteronism are at risk for renal damage, ocular damage, and stroke.

Sometimes when I talk to other veterinary people, either doctors or nurses, I get the impression that they fall into one of two categories: people who love diagnosing and managing feline endocrine cases, and people who would rather undergo an invasive medical procedure.

What is it about these cases that makes them so scary? In my mind, it’s probably the same stuff that makes them so interesting—there are no two cats that are alike, and there are no two feline endocrine cases that are alike. Anyone who works with cats knows not only do they refuse to follow the textbook, they take that book, shred it, and line their litter boxes with it.

Let’s talk about how to make some of the more common feline endocrinopathies a little easier to tackle.

Diabetes Mellitus

The 2018 AAHA Diabetes Management Guidelines for Dogs and Cats are a fantastic resource and have recently been updated. One of the most important messages of the guidelines is that you don’t necessarily need to be obsessed with chasing perfection in your diabetic cat patients. Perfection is great, and what a unicorn if you can hit it! Between cost limitations, client compliance, and patient compliance, though, we rarely get things exactly right.

Chronic diabetic cat cases are a great way to empower veterinary staff to educate clients and help them more effectively regulate their kitties. Moving away from in-hospital blood glucose curves has made things much less stressful on diabetic felines, but it also can make for more frequent and intense communication demands from clients. Continuous glucose monitors (CGMs) have probably been the biggest game-changer for diabetic cats and dogs. In addition to being a helpful way to monitor blood glucose trends, the discussions about the information CGMs provide can be a way to further bond clients to your practice team. Cat owners can scan and download glucose level trends and send that information along with notes about water intake and urine output, and trained staff members can have a telemedicine appointment to help guide the treatment plan. Regular laboratory and physical exam monitoring is clearly still important, but adding the extra level of communication and home monitoring is good for everyone involved—most of all, the diabetic cat.

Hyperthyroidism

Hyperthyroidism is the most common endocrinopathy in older cats. Historically, hyperthyroid cats presented with what we now call the “classic” clinical signs: increased appetite, weight loss, increased activity, and tachycardia. A lot of things have changed since the veterinary profession started diagnosing thyroid disease in cats, not the least of which is routine lab screening for our patients. This routine screening has allowed us to diagnose whole different populations of cats with thyroid disease, identifying them earlier and frequently before secondary damage to other organs can occur. Often these early diagnosed cats are younger, many of them younger than 10 years old. This presents us as a profession with a unique opportunity to aggressively tackle this curable disease, avoiding the significant side effects that can happen with longstanding, untreated hyperthyroidism.

Pearls of Wisdom

GettyImages-1173426119_[Converted].png• Owners know their pets better than we do, and listening when they believe something is wrong can save a pet’s life.

• Cost of I131 treatment may actually be less expensive in the long run for younger hyperthyroid cats, and maintaining a good relationship with a pet may be priceless for the owner.

• Starting methimazole prior to I131 treatment is not mandatory for most hyperthyroid cats.

• Don’t skip taking blood pressures! Figure out a way for your team to be successful.

• Allowing hypothyroidism to persist after thyroid treatment will accelerate chronic kidney disease.

The American Association of Feline Practitioners (AAFP) has a great set of guidelines for the diagnosis of hyperthyroidism. They have categorized cats with varying clinical signs and made it a little simpler to make decisions about cats without clinical signs or cats with clinical signs but incongruent lab values. The more we continue to do routine screening, the more subclinical hyperthyroid cats we will be able to identify. The most important takeaway from these guidelines is that cats with persistently high T4 levels, no matter what their presentation, need to be treated. Check out the guidelines at www.catvets.com.

TSH testing was not discussed in the AAFP guidelines. Although we think of this test more when we’re dealing with hypothyroid dogs, the thyroid-stimulating hormone (TSH) test can be useful for cats with early hyperthyroidism. Early hyperthyroid disease usually refers to cats who have minimal clinical symptoms, if any, and have a total T4 of under 4.5. In these cases, a TSH level will help show how much suppression of the normal thyroid tissue has occurred. This will be an important factor in deciding how these cases will be treated. If the TSH level is still measurable, there is a risk of damaging normal thyroid tissue when treating with radioactive iodine. Treatment with I131 should be postponed until the TSH is not measurable in borderline cats.

As mentioned before, all hyperthyroid cats need to be treated. Gone are the days of leaving the cat “a little hyperthyroid.” With few exceptions, the treatment of choice is radioactive iodine, especially now that we are diagnosing cats much sooner than we have in the past. An important update in hyperthyroidism management is that cats do not necessarily need to be treated with methimazole prior to receiving radioactive iodine. This is going to be a big change for many veterinarians, as we are all conscious of the possibility of concurrent chronic kidney disease being hidden by hyperthyroidism. Regardless of how the thyroid disease is managed, if there is also kidney disease, it will be exposed.

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Discussing hyperthyroid treatment, similar to discussing diabetic  management, is a key opportunity for nurses and staff to talk about concerns and roadblocks to treatment.

There is benefit to eliminating the constant whole body changes that the hyperthyroid state creates. When methimazole is chosen as the treatment option, over time, as the hyperplastic thyroid continues to grow, the cat will gradually become less regulated. As that happens, the thyrotoxic effects on the heart and kidney continue. By eliminating the hyperthyroid state completely, those hormone fluctuations can also be eliminated and the veterinary staff can focus on managing any other conditions without the constant interference of the thyroid.

Radioactive iodine treatment is a difficult choice for some owners because of cost, time away from home, age of the cat, and a general lack of understanding of how the treatment works. But those considerations only come into play if we are actually discussing this treatment. An important thing to remember as doctors and nurses is that we have to present all treatment options for a problem and stop making decisions for our clients. We are all guilty of bias sometimes, especially when it comes to financial judgments. We all love seeing our clients pull up in fancy cars, right? But are they always the ones who choose the ideal treatment plan?

Discussing hyperthyroid treatment, similar to discussing diabetic management, is a key opportunity for nurses and staff to talk about concerns and roadblocks to treatment. Cats are notoriously hard to medicate, and clients are sometimes willing to do more than we realize when they know that their relationship with their pets can be maintained by curing a disease with a single injection. Cost, distance, time away from home—these are all things that we may presume our clients don’t want to do, and we have to remember to keep our biases out of their decisions. Clearly not everyone has easy access to this treatment, but the sentiment is the same. Educate your clients, let your team members continue that education, and allow the cat owner to make the best decision they can.

Hypothyroidism

Hypothyroidism in cats can occur as a primary congenital problem, or most commonly as a secondary sequela to treatment for hyperthyroidism. Congenital hypothyroidism should be suspected in kittens who are slow to grow or present with constipation, lethargy, or just being a little dull. Diagnosis is usually straightforward, with low total thyroxine levels and elevated thyroid-stimulating hormone levels being diagnostic. Supplementation with levothyroxine is effective and lifelong.

Naturally occurring hypothyroidism in an adult cat is extremely rare, and a decreased T4 level is most commonly secondary to nonthyroidal illness. If an adult cat has a below-normal T4 level and has not been treated for hyperthyroidism, the cat should be screened for concurrent systemic disease. Improvement of the primary problem should allow the thyroid levels to normalize.

Iatrogenic hypothyroidism can be caused by overadministration of methimazole, thyroidectomy, or I131 therapy. The target T4 range for well-controlled hyperthyroid cats is between 1.0 and 2.5 ug/dL. Methimazole administration should be adjusted to reach this zone. After thyroidectomy or I131 administration, the T4 should normalize within three months. If the T4 remains lower than 0.8 after three months, supplementation with levothyroxine is indicated. Allowing hypothyroidism to persist will accelerate chronic kidney disease. It is not acceptable to allow the T4 to remain below normal.

Hyperaldosteronism

If you haven’t diagnosed a cat with hyperaldosteronism, odds are you’ve missed it. This disease can be subtle in presentation, and because cats are such challenging patients, it can be very easy to miss if you’re not paying close attention.

Excess aldosterone secretion is typically caused by either an adenoma or a carcinoma of the adrenal gland. Aldosterone is responsible for the regulation of potassium and sodium and contributes to water balance. Simplifying, the presence of excessive aldosterone creates a situation in which potassium is overly excreted and sodium is retained, leading to increased intracellular fluid and increased blood pressure.

The hallmarks of hyperaldosteronism are hypokalemia and systemic hypertension. Although most laboratories show a normal potassium level down to 3.6 or 3.7 mg/dL, anything under 4.0 mg/dL suggests whole-body depletion of potassium. Cats with hyperaldosteronism will usually be middle-aged to older cats, and low potassium may be noted on routine lab screening. With advanced hyperaldosteronism, the potassium may be lower than 3 mg/dL.

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Short appointment times, uncooperative patients, lack of staff technical skills, and false elevations because of stress and anxiety can all be factors for not having accurate, routine blood pressure measurements on feline patients.

Blood pressure screening should be done at least annually in middle-aged to older cats. In reality, this can be challenging. Short appointment times, uncooperative patients, lack of staff technical skills, and false elevations because of stress and anxiety can all be factors for not having accurate, routine blood pressure measurements on feline patients. Performing a retinal examination on all feline patients is quick and relatively easy. With practice, identifying tortuous retinal vessels and small retinal hemorrhages associated with longstanding hypertension becomes easier and is tremendously helpful in identifying true hypertensive cats. A retinal exam is not meant to be a substitution for actual blood pressure measurement.

Clinical signs of longstanding hyperaldosteronism include severe muscle weakness, ataxia, blindness, and retinal detachment. Earlier in the disease course, however, concerns from owners may be nonspecific. Affected cats may be somewhat lethargic or withdrawn because of the hypertension. People with hypertension frequently have headaches; being lethargic or withdrawn may be how our feline patients demonstrate the same symptom. The cats may be reluctant to jump up because of the declining potassium levels and subsequent muscle weakness.

As veterinary professionals, keeping an open mind about all of the differentials for vague symptoms is imperative. Owners know their pets better than we do, and listening when they believe something is wrong can save a pet’s life. The early signs of hyperaldosteronism could easily be attributed to other diseases or just to normal age changes. Most cats with early hyperaldosteronism do not show polyuria or polydipsia. This is important because hypertension and hypokalemia are frequent consequences of chronic kidney disease. Cats with refractory hypertension and hypokalemia should be additionally screened with plasma aldosterone concentration, which will provide a diagnosis in the majority of cases. Abdominal ultrasonography can identify an adrenal mass.

Left untreated, cats suffering from hyperaldosteronism are at risk for renal damage, ocular damage, and stroke. When possible, surgery is the treatment of choice for hyperaldosteronism. If surgery is not an option, either because the mass is unresectable or the owner chooses not to pursue, medical management can be effective. Medical management requires controlling the hypertension, supplementing potassium aggressively, and using spironolactone (an aldosterone receptor blocker) to help reduce the loss of potassium.

Primary Hyperparathyroidism

Primary hyperparathyroidism is a disease that we usually think about in our canine patients a whole lot more than our feline ones. It definitely isn’t as common as in dogs, but it is something to consider in cats.

Clinical signs of primary hyperparathyroidism are fairly nonspecific, with vomiting, lethargy, and decreased appetite being most common. Cats are more likely to have a palpable cervical mass than dogs, which may be mistaken for an enlarged thyroid gland. Hypercalcemia is present on routine lab testing and should be interpreted on fasted samples. Renal parameters may or may not be abnormal, but with renal secondary hyperparathyroidism, renal parameters will always be abnormal. Idiopathic hypercalcemia is the most common cause for elevated calcium in cats, but a complete workup for any calcium abnormality will include an ionized calcium level and a parathyroid hormone (PTH) concentration. Elevated ionized calcium, elevated PTH concentration, and a palpable cervical mass are consistent with a parathyroid mass and primary hyperparathyroidism. Treatment of choice is surgical removal of the mass, and the success rate for surgery is good.

Just like anything else in feline medicine, having patience dealing with the various endocrinopathies can make things go much more smoothly. Successful diagnosing and treating cats frequently requires more client communication, more creativity, humility, and perseverance.

Don’t panic, go one step at a time, and don’t be afraid to ask for help. 

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Renee Rucinsky, DVM, DABVP (Feline), is a graduate of the University of Missouri College of Veterinary Medicine and has been a board certified feline specialist for over 20 years.  In addition to routine feline wellness care, her hospital, at Mid Atlantic Cat Hospital and Mid Atlantic Feline Thyroid Center in Queenstown, Maryland, has become a busy referral center for complicated feline internal medicine cases, especially for diabetic cats.  Although kittens are great, Rucinsky is most drawn to geriatric care, endocrinology, and managing complex comorbidities in her feline patients.  When not working, you can find her out for a trail run or on her mountain bike, out on the paddle board, or sipping craft beers at a local brewery.

Photo credits: Sergeeva/iStock via Getty Images Plus; Slavica/E+ via Getty Images; Andrii-Oliinyk/iStock via Getty Images Plus; herraez/iStock via Getty Images Plus

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