Feline Hyperthyroidism: Debunking 5 Common Myths
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Hyperthyroidism is a common endocrinopathy in cats, with its prevalence climbing since it was initially reported in the literature in 1979.1,2 This disease can impact multiple organ systems and can be fatal if not treated.3 Thankfully, over time, understanding of feline hyperthyroidism has evolved, as have the available treatment options.3 Below are 5 myths commonly encountered with this condition and information to dispel those myths.
Myth 1: When a Cat Is Hyperthyroid, Clinical Signs Will Always Be Apparent to Either the Owner or the Veterinarian.
It might be easy for an owner to assume that their pet is disease-free if there have been no appreciable changes at home; however, routine health screening is critical for the detection of disease in apparently healthy patients.4 A 2024 study analyzed health screening results for 259 apparently healthy mature (7-10 years of age) and senior (>10 years of age) cats, meaning that owners had reportedly not observed any behavior changes, clinical signs, or alterations in body condition in their cat. A thorough history, physical examination, blood work, and urinalysis were performed. At the baseline visit, 21% of cats were diagnosed with a disorder, with 4.6% of the evaluated population being hyperthyroid.4 This study underscores the importance of routine health screening, including testing for hyperthyroidism in mature and senior cats, and provides useful information to share with owners of older cats if they are on the fence about routine health screening.4
Further, not all cases of feline hyperthyroidism will be apparent to the veterinarian on initial examination. The textbook presentation for feline hyperthyroidism is an active cat with weight loss in the face of an increased appetite.1 Presentation can also include polyuria/polydipsia, increased vocalization, agitation and other behavioral changes, tachypnea, tachycardia, vomiting, diarrhea, and/or an unkempt haircoat. Apathy, inappetence, and lethargy can also sometimes be seen.1 An examination may reveal a palpably enlarged thyroid gland, murmur, or arrhythmia.1 However, hyperthyroid cats can also be subclinical (elevated thyroxine [T4] with some physical examination findings suggestive of hyperthyroidism but no overt clinical signs reported by the owner) or clinically normal.1,3 The AAFP guidelines provide recommendations for when to re-evaluate cats that do not follow a classic presentation.1
Myth 2: A T4 Level in the Reference Range Rules Out Hyperthyroidism.
A diagnosis of hyperthyroidism is most commonly made based on the presence of clinical signs and an elevated T4.5 However, a T4 in the reference range does not necessarily rule out the condition.3,5 In hyperthyroid cats with moderate to severe concurrent conditions such as renal disease, diabetes mellitus, systemic neoplasia, primary hepatic disease, and/or other chronic systemic illnesses, serum T4 may be lower in the normal range, potentially masking hyperthyroidism.3,6 In addition, T4 levels can decline with age and also fluctuate day to day.3 When a cat has clinical signs and findings consistent with hyperthyroidism but total T4 is in the reference range, measuring free T4 by equilibrium dialysis or thyroid-stimulating hormone is indicated to diagnose hyperthyroidism.6
Myth 3: When It Comes to Medical Management of Hyperthyroidism, Options Are Limited to Pills & Compounded Formulations.
Although there was a time when medical management with methimazole was limited to tablets and compounded formulations, an FDA-approved oral solution, Felanorm® (methimazole) Oral Solution, is now available. Felanorm Oral Solution is honey-flavored, which can mask the inherent bitterness of methimazole, to help with acceptance of administration and has been recognized by the International Society of Feline Medicine with their “Easy to Give”™ certification.7,a The oral formulation also offers the practical ability of precise dose titration using the provided syringe, allowing clinicians to make fine adjustments as needed to achieve and maintain euthyroidism in individual patients. Further, oral administration can help reduce the potential health and safety risks associated with exposure to the transdermal gels,8 as well as the hurdles of pilling a cat.
Myth 4: Clients Will Let Their Veterinarian Know if They Are Having Challenges Medicating Their Cat.
It is tempting to assume that an owner will call if they are having trouble medicating their cat at home; however, in one study, only 41.8% of cat owners contacted their veterinarian to discuss their challenges, despite many reporting that medicating their cat had changed their relationship with their pet.9 In this study, cat owners rated tablets as harder to give than liquids overall, and more than half chose liquids as their preferred treatment formulation. Administration challenges can potentially damage the human–animal bond, and having an open dialogue regarding the owner’s experience and the range of formulation options may help with compliance and protect the human-animal bond.9
Myth 5: For Cats on Methimazole, Recheck T4 Levels Need to Be Properly Timed Postadministration.
Proper follow-up for some endocrine conditions requires monitoring tests be performed within a particular window after medication is received (3 weeks after starting therapy or sooner if signs persist); however, T4 levels can be checked at any time of day for hyperthyroid cats receiving medical management with methimazole, allowing for recheck visits to be scheduled at a time that works best for the owner’s schedule.3
Conclusion
Initial presentation of feline hyperthyroidism can vary, and diagnosis can range from straightforward to more complicated. Educating clients on the benefits of screening, the range of clinical presentations, and the growing number of treatment options may help improve overall patient care. A key factor in successful long-term management is ensuring owners are comfortable medicating their cat. Felanorm Oral Solution offers a convenient, titratable, oral option that eliminates the stress of daily pilling for both the pet and pet owner.
IMPORTANT SAFETY INFORMATION
Felanorm® (methimazole) Oral Solution: As with all methimazole products, wear protective single use, impermeable (e.g., latex or nitrile) gloves when administering the solution. The most commonly reported side effects in cats are anorexia, vomiting, head/facial pruritus or edema, depression/lethargy, weight loss, anemia, elevated liver enzymes, skin lesions, elevated BUN, diarrhea, and thrombocytopenia. In some reported cases, the patients recovered after adverse reactions were recognized, the drug was withdrawn, and veterinary care was applied. Methimazole has anti-vitamin K activity and may induce bleeding diathesis without evidence of thrombocytopenia. Not for use in pregnant or lactating queens. Not for use in cats with primary renal or hepatic failure, autoimmune disease, or with hematological disorders (see the full prescribing information for additional details). For full prescribing information, contact VIRBAC at 1-800-338-3659 or click here.
a ISFM Easy-to-Give award 2017 (Note: Thyronorm® is the UK version of Felanorm; exact same formulation).
