Radioiodine treatment in hyperthyroid cats: insights into the characteristics of owners and their cats,and owner motivation and perceptions

Abstract

Objectives

Radioiodine (¹³¹I) therapy is the most appropriate treatment option for many hyperthyroid cats, as it is minimally invasive and often curative. Nevertheless, ¹³¹I treatment is not always pursued by owners. Hence, it is important to obtain more insight into owner satisfaction during and after ¹³¹I treatment, and their decision-making process. In this study, we describe the characteristics of owners and their hyperthyroid cats referred for ¹³¹I therapy, and determine owners’ motivation and how they experienced the ¹³¹I treatment of their cat.

Methods

A survey was sent to owners whose cats underwent ¹³¹I therapy (n = 1071) between 2010 and 2017 at Ghent University. The survey contained 35 questions with tick-box or free-text answer options concerning family situation, pet insurance, previous therapy, comorbidities, motivation for ¹³¹I therapy and owner perception of this treatment.

Results

In total, 438 owners completed 94% or more of the questionnaire. Over half of the cats (55%) had received previous medical, dietary or surgical treatment. Motivations for changing the initial therapy to ¹³¹I therapy included difficulties in administering medication (31%), insufficient improvement in clinical signs (23%), side effects (16%) and following the referring veterinarian’s advice (16%). Almost a fifth of owners (18%) were not informed about the existence of ¹³¹I therapy by their veterinarian and found information on ¹³¹I treatment online or through friends. Hospitalising their cat was very distressing for 17% of owners. Most owners (92%) were satisfied with the treatment. Reasons for dissatisfaction were insufficient communication, iatrogenic hypothyroidism, persistent hyperthyroidism and comorbidities post-treatment.

Conclusions and relevance

Our study stresses the importance of communication regarding the possible outcome of ¹³¹I treatment, the importance of managing underlying comorbidities before treatment and anticipating the stress of owners during their cat’s hospitalisation period. The results of this study could help in improving client communication when advising on ¹³¹I treatment.

Keywords

Hyperthyroidism survey owner motivation owner perception

Introduction

Feline hyperthyroidism (FHT) is the most common endocrine disorder in elderly cats, with an estimated prevalence of up to 10% in cats over the age of 10 years.¹

Different treatment options include oral or transdermal thyroid inhibitors (eg, methimazole), an iodine-restricted diet, thyroidectomy or radioiodine (¹³¹I) therapy. These options vary greatly in cost, possible complications and success rate.^2–4 Long-term medical management can lead to a progressive increase of tumour size and the development of malignancy.^5–7 Dietary therapy is not curative and has a lower success rate in controlling FHT.^{8–10 ¹³¹}I therapy and thyroidectomy are the only potentially curative options.^2,3 Thyroidectomy is invasive, requires general anaesthesia and does not treat ectopic thyroid tissue.² ¹³¹I treatment is considered the gold standard treatment for many cats.^11,12 It has a high curative rate (>95%), treats all abnormal thyroid tissue (including ectopic thyroid tissue), is minimally invasive and general anaesthesia is not required.^2,3

Previous studies show a significant improvement in the quality of life (QoL) of both ¹³¹I-treated cats and their owners, although this relates to the treatment outcome whereby owners of cured cats give higher QoL scores.^{2,13 ¹³¹}I therapy eliminates the burden of daily medication or exclusively feeding an iodine-restricted diet for the vast majority of cats.^2,14

The objectives of this study were to determine owner motivation for ¹³¹I treatment for their hyperthyroid cat and to understand their perception of ¹³¹I treatment.

Materials and methods

The owners of cats that underwent ¹³¹I therapy between January 2010 and December 2017 at Ghent University were contacted by email, SMS or post. An online questionnaire consisting of 35 questions with tick-box or free-text answer options was compiled using the online survey tool SurveyMonkey (see supplementary material). The survey contained questions concerning family situation, pet insurance, previous treatments, comorbidities, motivation and owner experience of ¹³¹I treatment. The survey required approximately 10–15 mins to complete. Owners could choose whether to complete the questionnaire in English or Dutch. Two reminders were sent with a 2–3 week interval. Data were merged into a Microsoft Excel spreadsheet for further analysis. Descriptive statistics were performed on the data in Microsoft Excel.

Results

A total of 1071 owners were contacted: 680 by email, 457 by SMS and three by post. Of these owners, 41.6% (n = 446) responded by filling out the questionnaire. Only surveys with 94.0% or more of the questions completed (n = 438) were used for this study.

Owners

Respondents were aged <20 years (1.6%), 21–40 years (30.0%), 41–60 years (57.0%), 61–80 years (10.7%) and >80 years (0.7%). More than half of the owners (51.6%) were from the Netherlands, 40.9% of owners were from Belgium and 5.0% were from Germany. Other countries each accounted for <1%. Owners who did not have children accounted for 40.8% of respondents; 37.6% of owners had older children (⩾11 years) and 21.6% had young children (⩽10 years). There were five (1.1%) households where there was a pregnant woman residing.

Cats

The cats’ ages at the time of diagnosis of FHT are shown in Table 1. Female cats (54.3%) were over-represented. Of the cats, 70.5% lived both indoors and outdoors; 28.3% of cats lived exclusively indoors and 1.1% lived exclusively outdoors. Fifteen owners (3.4%) had medical insurance for their pets.

Table 1

Age of 438 cats at the time of diagnosis of hyperthyroidism

Age (years)	n (%)
3–6	9 (2.1)
7–10	98 (22.4)
11–14	280 (63.9)
⩾15	51 (11.6)

The most concerning clinical sign of FHT was weight loss (269 owners; 61.4%), restlessness (40 owners; 9.1%) and polyuria and polydipsia (PU/PD; 34 owners [7.8%]). Rapid condition loss was of greatest concern for 31 owners (7.1%); 23 owners (5.3%) were troubled by their cat’s gastrointestinal signs and five owners (1.1%) by their cat’s aggression. No clinical signs were noticed (incidental diagnosis during senior screening) in 10 cats (2.3%).

Over half of the patients (61.6%) had no known comorbidities prior to ¹³¹I therapy, according to the owners. The most common comorbidities mentioned by owners were cardiac disease (8.7%) and chronic kidney disease (CKD; 8.2%). Additional comorbidities specified by owners included feline lower urinary tract disease, diabetes mellitus, dermatological disorders, unspecified gastrointestinal signs, dental disease, feline immunodeficiency virus, pancreatitis, respiratory disease, orthopaedic disease, otitis, conjunctivitis and megacolon.

Therapy

Figure 1 shows how owners first received information on ¹³¹I therapy for their cat. Table 2 shows the time between diagnosis of FHT and ¹³¹I therapy. Three cats were treated >5 years after the diagnosis of FHT.

Figure 1

Source of information where owners first learned about ¹³¹I therapy

Table 2

Time between the diagnosis of feline hyperthyroidism and ¹³¹I therapy in 437 cats

Interval	n (%)
<2 months	207 (47.4)
2–6 months	135 (30.9)
6–12 months	49 (11.2)
1–2 years	28 (6.4)
>2 years	18 (4.1)

In 54.6% of cats, one or multiple other treatment options were attempted before opting for ¹³¹I therapy, while 45.4% of cats received no other treatment for FHT prior to ¹³¹I therapy. Of the cats that received prior treatment, 214 (77.0%) were administered thyroid inhibitors, 58 (20.9%) received an iodine-restricted diet and six (2.1%) had undergone thyroidectomy. In some cats a combination of multiple treatments was attempted.

The reasons for changing the initial treatment to ¹³¹I therapy included difficulties administering medication (31.2%), lack of improvement of clinical signs with the previous treatment (24.0%), the advice of the referring veterinarian (16.7%) and the presence of too many or severe side effects (16.2%). Medicinal side effects included dermatological reactions and pancytopenia caused by thyroid inhibitors. Nine cats (4.1%) did not like the iodine-restricted diet, causing the owner to change the therapy. Five owners (2.3%) experienced the administration of medication as too time consuming. Finally, three owners (1.4%) stopped the initial treatment owing to the long-term financial costs associated with medical treatment with thyroid inhibitors.

Considering all owners, the main motivation for choosing ¹³¹I therapy was to improve the health of their cat (56.6%). A fifth of owners (20.6%) opted for ¹³¹I therapy ‘out of love for their cat’. Some owners could not or did not want to administer daily medication (10.8%) and 6.9% stated that previous treatment did not show satisfactory results. The long-term financial benefits inspired two owners (0.5%) and another two owners (0.5%) felt they were under social pressure to choose ¹³¹I therapy. Other reasons for choosing ¹³¹I therapy applied to 4.1% of owners.

At Ghent University, patients were checked in on Monday and discharged on Friday (at the earliest). Figure 2 depicts how owners perceived the obligatory hospitalisation period.

Figure 2

How owners perceived the obligatory hospitalisation period where they were not able to visit their cat

In total, 412 cats (94.1%) received one ¹³¹I treatment. Twenty cats (4.6%) needed two treatments, four (0.9%) needed three treatments and two (0.5%) needed more than three treatments, according to their owners.

Owners noted an improvement in clinical signs of FHT within 1 month (46.4%), within 1–6 months (34.4%) and within 6 months to 1 year (1.8%). Symptoms persisted in 7.6% of cases. The other owners could not remember when their cats’ clinical signs improved.

In the first 6 months after ¹³¹I therapy, 51.2% of owners did not notice clinical signs related to possible comorbidities or complications of ¹³¹I therapy. Other owners mentioned CKD (9.8%), iatrogenic hypothyroidism (5.6%), cardiac disease (2.3%), constipation (2.1%), obesity (3.5%), vomiting (5.0%), lethargy (5.2%) and miscellaneous signs (15.2%).

At the time of survey completion, 44.7% of cats were still alive. Within 6 months after ¹³¹I therapy, 10.3% of cats had died; 16.2% of cats had died between 6 months and 2 years after ¹³¹I therapy and 28.7% had died between 2 and 5 years after ¹³¹I therapy. With regard to cause of death, owners mentioned neoplasia, renal disease, heart failure, old age/euthanasia, stroke, trauma, hepatopathy and miscellaneous causes (intoxication, feline infectious peritonitis, pancytopenia, feline asthma). Three cats died or were euthanased owing to a relapse of FHT.

Altogether, 388 participants (88.6%) would recommend ¹³¹I therapy. Nine owners (2.1%) were neutral and 41 (9.4%) would not recommend the treatment. Overall, owners were very satisfied (n = 321; 73.5%) or satisfied (n = 84; 19.2%) with the service provided at Ghent University, 4.8% (n = 21) were neutral and 2.5% (n = 11) were dissatisfied. Reasons for dissatisfaction or not recommending treatment included insufficient information on iatrogenic hypothyroidism, unmasking of CKD post-treatment, stress during the consultation (especially if many students were present), long waiting times, a lack of cat friendliness in the waiting room, insufficient communication during hospitalisation, a lack of active follow-up and the development of other diseases post-treatment.

Suggestions to improve the service included improved communication during the hospitalisation period, photo or video updates, improving the cat friendliness of the waiting room and consultations, more intensive follow-up, more information on possible complications and a reduced price. Almost all owners (98.4%) agreed with the statement that they received clear and understandable information on ¹³¹I therapy before treatment, and 89.0% agreed that they received adequate home care instructions at discharge.

Discussion

¹³¹I treatment is often considered the gold standard therapy for FHT. Insight into the client population and owner motivation and perception is valuable in supporting owners in their decision-making process and improving the care of ¹³¹I-treated hyperthyroid cats.

Owners aged 41–60 years were represented more than any other age group. This is comparable to the age group in which individuals start earning higher salaries.¹⁵ Thus, a possible explanation may be the fact that owners in this age group can potentially afford a higher-cost treatment more easily. The cost of ¹³¹I therapy during the period in which the cats in this survey were treated was approximately €750, including hospitalisation.

A mere 3% of owners had medical insurance for their pets. Veterinary medical insurance is a relatively new phenomenon in Belgium and the Netherlands. In the UK, up to 55% of cats referred for ¹³¹I therapy are insured.¹³ In a study performed in the UK owners of uninsured cats were less likely to pursue ¹³¹I therapy, despite ranking cost as a factor with a low impact on their decision to pursue ¹³¹I therapy.¹³ In our study, owners considered cost as a factor that had a low impact on their decision. Of course, we included only owners who had pursued ¹³¹I therapy, which probably resulted in a selection bias. Social desirability may also have had an influence on owners. In the free-comment section, several owners suggested lowering the price of ¹³¹I therapy to make it more affordable. With the appearance of more pet insurance companies and increasing owner awareness of pet insurance, medical costs will probably be less of a limiting factor in the future.

Pregnant women were present in 1% of all households and young children were present in 22% of households. Radioprotective measures were explained during consultations, on websites and in information brochures. It was stated that, if the owner was pregnant or had young children, they must keep the cat separate for 2 weeks or leave the cat in the ¹³¹I facility at an additional cost.

The majority of cats were diagnosed with FHT at between 11 and 14 years of age. Only 25% of cats were younger than 10 years of age. This compares to the findings of Watson et al, where 30% of cats diagnosed with FHT were aged 10 years or younger.¹⁶ In our population, only 12% were 15 years of age or older. Other studies stated that the owners of cats aged ⩾15 years were less likely to pursue ¹³¹I therapy, and owners who opted for antithyroid medication commonly gave old age as a reason for opting for medical treatment.^13,14

Watson et al indicated that as many as 24% of cats were incidentally diagnosed with hyperthyroidism.¹⁶ In our study, 10 owners (2%) did not notice clinical signs of FHT in their cats. These cats were diagnosed with FHT during a routine check-up. It is likely that many hyperthyroid cats remain undiagnosed until obvious clinical signs such as weight loss appear. More subtle clinical signs such as PU/PD may remain unnoticed by owners; in our survey only 8% of owners noted PU/PD in their cat. Our results, together with previous research from our group, emphasise the importance of regular health checks, including thyroid function testing, for elderly cats.¹⁷ Early diagnosis and subsequent treatment of FHT prevents severe clinical signs (eg, weight loss and thyrotoxic cardiomyopathy).¹⁶

Over 60% of cats had no known comorbidities according to the owners, even though >75% of patients were older than 10 years at the time of ¹³¹I therapy. Owners of cats with concurrent diseases are possibly less likely to pursue ¹³¹I therapy. Also, veterinarians may consider these cats as poor candidates for ¹³¹I therapy and are possibly less likely to refer them. Comorbid diseases were probably undiagnosed in some cats since 10% of cats died within 6 months after ¹³¹I therapy. A few cats in our study had neoplasia, which was diagnosed only after ¹³¹I therapy, and these owners regretted having pursued ¹³¹I therapy. Puig et al found that 18% of cats that appeared to be good candidates for ¹³¹I therapy based on history and clinical examination had concurrent non-renal diseases such as inflammatory bowel disease or alimentary lymphoma.¹⁸ These owners all decided not to continue with ¹³¹I therapy. Another study found that as many as 30% of cats referred for ¹³¹I therapy had major comorbid disease that could influence treatment decisions.¹⁹ At Ghent University, the medical files of all cats are screened by a veterinarian before an appointment is scheduled. If there are any indications for comorbidities, the cats are first seen by the endocrinology service. Our current initial screening is based on history, physical examination and blood examination. Medical imaging is pursued only if there are medical indications. In a study where abdominal ultrasonography was routinely performed on all cats referred for ¹³¹I therapy, ultrasonographic abnormalities were found in 36% of cats. However, ¹³¹I therapy was subsequently not pursued in only 2% of cats.²⁰

Our research emphasised that the vast majority of owners were referred by their primary care veterinarian, and only 18% of owners learned about ¹³¹I therapy by other means such as online sources or friends. Online sources included social media and websites. However, this information might not always be scientifically correct. In our survey, only owners who had chosen ¹³¹I therapy for their cat participated. We can assume that more owners are unaware of this treatment option. In the UK, a survey showed that 53% of owners of hyperthyroid cats treated in first-opinion practices were unaware of ¹³¹I therapy.¹³ Another UK survey showed that 30% of owners of hyperthyroid cats were offered only antithyroid medication as a treatment option.¹⁴ This could indicate a current knowledge gap among general practitioners. Another possible reason is that veterinarians are not familiar enough with referral for ¹³¹I therapy and are hesitant to discuss this option with owners. In Australia, veterinarians preferred ¹³¹I therapy, but despite this preference few patients were referred due to perceived cost and underestimation of the success rate of ¹³¹I treatment by the veterinarians.²¹ This might be similar among Belgian and Dutch veterinarians.

The main motivation for owners to opt for ¹³¹I therapy was to improve their cat’s health. Reasons for changing a prior treatment to ¹³¹I therapy included, among others, difficulties in administering medication (31%). This is in line with previous research: in a study that compared oral and transdermal thyroid inhibitors, 35% of owners were struggling to administer oral tablets.²² Difficulty medicating their cat was the main reason to pursue ¹³¹I therapy for 44% of owners in the survey of Boland et al.¹³

The required hospitalisation period was stressful for many owners, despite a much shorter hospitalisation period (5 days) than in the UK (2 weeks) at the time the cats were treated. The emotional impact of this period of separation on owners should not be underestimated. Of the owners who did not recommend ¹³¹I therapy, several mentioned that they would not want to hospitalise their cat again. Several owners made suggestions to improve communication during the hospitalisation period. A veterinary nurse now gives daily updates to owners by email or telephone. Also, the hospitalisation period has now been decreased to 4 days. Other owner suggestions were implemented at our clinic to improve the experience of owners and their cats, such as a separate waiting room and consultation room for cats.

Six percent of cats treated with ¹³¹I in our study needed more than one ¹³¹I treatment. It should be assumed that the actual number may be higher since many owners do not consider a second treatment if it is needed. Multiple treatments may be necessary, especially in patients with thyroid carcinomas or patients with very large thyroid glands. A thyroid adenoma can transform into a thyroid carcinoma.^5–7 Multiple treatments can also be needed if a cat develops new thyroid adenomas or if the first treatment fails.²³

The reported incidence of iatrogenic hypothyroidism ranges between 5% and 30%, depending on the ¹³¹I dose protocol.^2,24,25 Most studies describe an incidence of <9%.^2,24,26 Iatrogenic hypothyroidism causes a decline in renal function, which can lead to azotaemia post-treatment and a decreased survival time.²⁷ In 6% of cats in our study, owners mentioned the development of iatrogenic hypothyroidism within 6 months post-treatment. This is a good result and in line with the current literature on the use of lower ¹³¹I doses to avoid iatrogenic hypothyroidism.^24,26,28 However, the real incidence of iatrogenic hypothyroidism is probably underestimated due to recall bias or lack of follow-up. There could also be an overestimation if thyroid hormones were monitored too early and the cat had transient hypothyroidism.

Six owners felt that the risk of iatrogenic hypothyroidism was minimised during pretreatment discussions. Understandably, some participants chose ¹³¹I therapy because they did not want to administer daily medication. After the ¹³¹I treatment, they still ended up in a position where they had to administer daily medicine for iatrogenic hypothyroidism. Although this was inconvenient for the owner, the thyroid tumour was treated with ¹³¹I therapy, which prevents possible transformation to a carcinoma.⁵

This study has several limitations. In several cases there was a long time between ¹³¹I therapy and the survey. To have a sufficient response, the questionnaires were sent to owners of cats that were treated between 2010 and 2017, which probably resulted in recall bias.

There were limitations of question design. Some categories for the time interval from diagnosis to ¹³¹I therapy and improvement in clinical signs overlapped.

There was no active follow-up besides medical advice in the clinical report and via email to the referring veterinarian. The results of the further examinations, such as bloodwork, could not be verified. The presumed thyroid status, comorbidities and cause of death were based on the owner’s information.

Conclusions

The results of this study can aid client communication. Veterinary awareness of ¹³¹I therapy can be improved. Overall owner satisfaction was good, but could be improved by clear communication on the potential outcomes of ¹³¹I treatment and possible comorbidities. Adequate communication during hospitalisation is essential to alleviate the stress of the owners.

Supplemental Material

sj-docx-1-jfm-10.1177_1098612X221150191 – Supplemental material for Radioiodine treatment in hyperthyroid cats: insights into the characteristics of owners and their cats, and owner motivation and perceptions

Supplemental material, sj-docx-1-jfm-10.1177_1098612X221150191 for Radioiodine treatment in hyperthyroid cats: insights into the characteristics of owners and their cats, and owner motivation and perceptions by Charlotte De Voogt, Lianie Williams, Lisa Stammeleer, Kathelijne Peremans, Eva Vandermeulen, Dominique Paepe and Sylvie Daminet in Journal of Feline Medicine and Surgery

Footnotes

Accepted: 21 December 2022

Author note

The results of this study were presented as an abstract at the Deutsche Veterinärmedizinische Gesellschaft (DVG) congress 2022 (online).

Supplementary material

The following file is available online:

Questionnaire: radioiodine treatment in hyperthyroid cats.

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Ethical approval

The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS.

Informed consent

This work did not involve the use of animals (including cadavers) and therefore informed consent was not required. No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.

ORCID iD

Charlotte De Voogt

Lisa Stammeleer

Eva Vandermeulen

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Supplementary Material

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