Feline hyperthyroidism (FH) is described as being the most common endocrinopathy seen in cats, and one of the most frequently diagnosed conditions in small animal practice (Mooney, 2002).
In order to provide the highest levels of patient care, it is essential that registered veterinary nurses (RVNs) have a deep understanding of the condition, including clinical signs, methods of diagnosis and treatment options available. Whether looking to provide long-term management or to facilitate curative treatment, effective owner communication is an important factor to consider.
The RVN plays a vital role in discussing care of patients with owners. It is important that RVNs are able to deliver current, accurate information so owners can feel confident and supported when making decisions regarding the care of their pet. The aim should be to help owners to understand benefits, potential complications and longer term considerations of treatments available. Communication is an important core skill, playing a vital part in ensuring owner satisfaction and continuing practice success (McDermott et al, 2015). Other advantages of good communication between practitioner and owner are recognised as improving the health care received by the pet, increasing job satisfaction, facilitating reductions in practice complaints while increasing overall customer satisfaction (Barton, 2010).
FH commonly affects middle to old aged cats and is rarely seen in cats younger than 10 years (Peterson, 2006). FH is a multisystemic disorder resulting from excessive circulation of total tetraiodothyronine (T4) and total triiodothyronine (T3) within the blood. It affects male and female cats equally and is seen in all breeds (Peterson, 2012), although considered rare in pure breeds (Figure 1), especially Siamese and Himalayans (Wakeling et al, 2009).
Clinical signs
Common clinical signs comprise weight loss, polyphagia, polydipsia, polyuria, vomiting, diarrhoea and irritability. Due to the potential for concurrent systemic disease it is not uncommon to see patients present with decreased appetite, depression and weakness (Peterson, 2006). Other recognised signs include tachycardia, increased activity, restlessness, poor coat condition and intolerance to heat (ISFM, 2017). A heart murmur and gallop rhythm may also be detected on cardiac auscultation (PETMD, 2017).
The initial role of the RVN is promoting awareness and helping owners to recognise illness or abnormalities in the behaviour and general demeanour of their cat. Some owners may perceive the signs associated with FH as normal changes related to old age and RVNs can assist in raising awareness of the condition and reducing this occurrence. Geriatric pet clinics (ran by RVNs) can be excellent in providing early detection of FH. As discussed by Spencer (cited in Barton, 2010) owners are often more relaxed when speaking to RVNs due to perceptions that they use language that is easier for them to understand. Owner discussion may result in owners mentioning changes in their cat's routine, such as amount of food consumed or differences in temperament. This can happen sooner than an owner recognising a specific problem and actively seeking veterinary advice.
Physical examination
Physical examination is closely linked to clinical signs. Weight loss or signs of cachexia should be duly noted. Auscultation of the heart and routine pulse taking will detect tachycardia in patients and signs of hypertension and diarrhoea should also be observed. The presence of goitre can also be detected on physical examination and RVNs should feel confident that they have the skills to perform this.
The thyroid gland is located in the neck area, adjacent to the trachea and distal to the larynx. The gland is bilateral, vascular and one of the largest endocrine glands. There are two recognised methods for palpating the gland and both should be undertaken during examination (Peterson, 2013). All hyperthyroid cats will have a thyroid nodule, unilaterally or bilaterally, although not palpable in all cats, additionally some euthyroid cats will have a palpable goitre (Peterson, 2013).
The initial technique involves examining the cat with their neck slightly extended and the head tilting backwards. The thumb and index finger are passed gently over both sides of the trachea. It is important to start at the laryngeal area and move down towards the thoracic inlet.
The second technique, often referred to as the Norsworthy technique, requires the RVN/clinician to be positioned directly behind the cat with the head raised and turned 45° to the right or left (away from the side being examined). The index or middle finger is placed in the groove formed by the trachea and sternothyroid muscle (just below the larynx), and fingers are moved downwards within the groove towards the thoracic inlet (Peterson, 2013).
The thyroid gland may not be palpable in all cases of FH as it is possible for the affected lobes to descend into the thoracic cavity due to their loose attachment to the trachea, or for ectopic hyperfunctional thyroid tissue (EHTT) to be present (Peterson, 2013).
Diagnosis
While it is important to remember than RVNs cannot diagnose, full understanding of the diagnostic process can improve owner communication.
Once suspected, the condition needs to be formally diagnosed. Effective diagnosis combines physical examination of the cat alongside history and current signalment. Routine biochemistry, complete haematology and urinalysis should be undertaken, enabling detection of concurrent disease as many conditions can mimic the symptoms of FH (Peterson, 2013). Specific thyroid function testing should always be completed (Peterson, 2006).
When considering diagnosis of FH, it is worth remembering the condition may lead to other abnormalities including changes in the muscular wall of the heart, leading to heart failure if left untreated. Investigations into cardiac disease should be carried out where necessary. Many hyperthyroid cats present as hypertensive and blood pressure measurements should be obtained at diagnosis and as part of on-going care. Concurrent chronic kidney disease is a common complication of FH due to the age of affected patients (ISFM, 2017).
Blood testing
Specific testing involves investigating T4 levels (often referred to as total T4) within the blood. This is one of the hormones released by the thyroid gland and appears elevated in over 90% of cases (Peterson, 2013). Most T4 and T3 hormones circulate in blood bound to protein, and are affected by the amount of protein in the blood that is available to bind to the hormone. Measurement of serum T3 levels provide less advantageous results as these appear to not elevate in a third of hyperthyroid cats (Taylor et al, 1989; Peterson, 2013).
Free T4 (FT4) is the small percentage of T4 that is free and not bound to protein, it is the active form of thyroxine and not affected by protein levels. This is important to remember when assessing patients for concurrent renal disease as an increase in blood urea nitrogen (BUN) and creatinine, indicative of renal disease, may not become apparent until T4 levels normalise. Although FT4 is considered more sensitive in enabling diagnosis of hyperthyroidism, available tests convey an increased incidence of false positives in euthyroid cats and false negatives in cats with concurrent disease processes (Peterson, 2013).
Serum T4 can be suppressed if the cat is suffering from other significant disease processes. It is important to remember to re-test T4 levels once the patient has been treated for other disease processes effectively. Thyroid levels often increase following successful treatment of concurrent disease.
There are many T4 assays available for use although none are 100% sensitive. All of the commonly used assays have their individual limitations and there is currently no perfect test that can simply confirm or exclude thyroid disease (Peterson, 2013). Table 1 details the main points in regards to the various assays.
| Assay Type | Advantages | Disadvantages |
|---|---|---|
| Radioimmunoassays (RIA) | Most accurate — considered to be the gold standard | Reduced availability due to regulations on the use of radioactivity Costly |
| Chemiluminescent enzyme immunoassays (CEIAs) | Similar accuracy to RIA method More widely used as does not involve radioactive isotopes | Not as accurate as RIA |
| Point of care enzyme-linked immunosorbent assays (ELISA) | Allows for in-house testing Cost efficient | Unreliable as consistently over estimate T4 levels |
| Enzyme immunoassays (EIA) | Can be run alongside routine biochemistry allowing for speedy results Cost efficient | Often results in under estimation of T4 |
| Human assays | Not validated for use in cats or dogs Lack of sensitivity in measuring lower T4 concentrations (not suitable for cats) |
Thyroid scintigraphy
Considered the gold standard in diagnosis of FH (Peterson, 2013), this is an area where specific RVN knowledge may be lacking. Scintigraphy is a nuclear medicine procedure, whereby the patient receives an intravenous injection of a radionuclide (Technetium 99) that is concentrated by thyroid tissue. It is a highly useful diagnostic tool and it is essential for nurses to feel confident in advising owners why and how it could be beneficial to their pet. Thyroid scintigraphy produces a visual display of functional thyroid tissue, including EHTT, often present in the neck, thoracic inlet and thorax.
One of the main benefits of scintigraphy is the ability to achieve an early diagnosis due to the visualisation of functional thyroid tissue (Figure 2). This can be seen on scans before laboratory tests provide results that are consistently abnormal. With the use of scintigraphy, the severity of thyroid disease can be determined and hyperthyroidism in euthyroid cats that have false-positive T4 elevations excluded (Peterson, 2013).
Owners should be aware that this expensive diagnostic tool is not widely available and requires their cat to be hospitalised for 24–48 hours. In addition, the potential differentiation between thyroid carcinoma and benign thyroid disease is unreliable when performing scintigraphy (Harvey et al, 2009) and discussions explaining the implications of this should take place prior to scanning.
The importance of scintigraphy prior to treatment was emphasised in a study by Harvey et al (2009), which revealed that many cats diagnosed with FH had areas of EHTT. This area was present in cats that had yet to receive treatment and in many that had already undergone surgical thyroidectomy. Ectopic thyroid tissue presents a real complication for patients and scintigraphy is required for identification, allowing implementation of the best treatment regimen.
Treatment
Spontaneous remission of hyperthyroidism does not occur and due to the adverse effects on the body, treatment is a necessity. Following diagnosis and initial discussion with the veterinary surgeon, it may be acceptable for an experienced and subject confident RVN to discuss these various options.
Owners should be aware of the differences between treatments that aim to manage the disease and those that may prove curative. Oral and transdermal treatments plus the use of iodine-restricted diets fall into the management category whereas surgical thyroidectomy and radioactive iodine (RAI) treatment may prove curative (Bodey, 2015).
By using scintigraphy as part of the diagnostic regimen, veterinary professionals are able to offer better advice to owners on the best method of treatment for the individual pet. Scintigraphy can enable the veterinary practitioner to feel confident in whether surgical thyroidectomy or RAI would prove curative.
Good communication with owners can enhance the care of patients, leading to improved relationships between owners and practice (Hedberg, 2016). In translation, if owners fully understand the diagnostic process and procedures available to gain an exact diagnosis, they can make informed decisions and have greater understanding regarding the possibility of complications following treatment. RVN involvement in this area is paramount in helping owners understand the options available to them, the benefits and risks of each treatment and the impact on the life of both cat and owner.
Nurse consultations have become a valued aspect of veterinary practice and many owners feel more at ease asking an RVN questions than a veterinary surgeon (Bowden, cited in Barton, 2010). Once a thorough yet relaxed conversation in regards to treatment has taken place, the owner can have time to digest the information and return to the veterinary surgeon to discuss their thoughts.
Medical management
The most commonly used drugs in the treatment of feline hyperthyroidism are methimazole (oral/transdermal) and carbimazole (oral) (Frénais et al, 2009). The benefits for their use are multiple, including reducing T4 levels prior to surgical thyroidectomy, which can improve the safety of anaesthesia. Medical treatment is reversible which is useful should underlying renal insufficiency be detected following onset of treatment and normalisation of T4 levels (Trepanier, 2006).
While medical management is considered most affordable by owners, it is the responsibility of practice staff to ensure that effective communication has taken place with the owner and they understand that this is a treatment and not curative, so medical management requires life-long commitment and cost. Owners should be aware that despite initial high costs for other forms of treatment, long-term costs associated with medical management may actually be greater especially when the necessity for repeat thyroid and biochemistry blood analysis is considered. Owners should also be made aware that in some cases of medical management, benign tumours continue to grow and the risk of malignancy increases (Peterson, 2012).
Methimazole ideally requires twice daily dosing as it has been proven to be less effective if administered once daily (Trepanier, 2006). Carbimazole (controlled release) offers owners the opportunity for once daily dosing and is therefore believed to increase owner compliance, however renal parameters have been shown to deteriorate in many cats when receiving controlled release carbimazole (Frénais et al, 2009). It may be concluded that methimazole is the preferred drug for medical management due to efficacy and lower incidence of side effects (Trepanier, 2006). The success rates of medical management may be directly affected by the owner's ability to pill the patient. RVNs are highly skilled in this area and should be encouraged to demonstrate effective administration of oral medications to the client.
Diet
There are still many conflicting views in regards to dietary management of FH. It has been suggested by many that diet plays a definite role in the aetiology of the disease (Wakeling et al, 2009; Edinboro et al, 2010; Peterson, 2012), attributed to levels of iodine supplementation found in commercial cat foods.
Thyroid hormones affect the entire body, causing issues with multiple organs and body systems (concurrent renal, hepatic and gastrointestinal issues are common in hyperthyroid cats). It is therefore essential that diets fed are able to meet a multitude of needs and not prove detrimental to other body systems.
Weight loss and muscle wastage are common clinical signs of FH and increased protein catabolism can lead to negative nitrogen balance, resulting in the body consuming its own muscle tissue as a substitute protein source (Peterson, 2011). It is essential that affected cats receive a good source of dietary protein, enabling rebuilding of muscle mass.
It may be concluded that the ideal diet for FH is one of high dietary protein (of high biological value) and low dietary carbohydrate. Many over the counter foods fulfil these needs and it may not be necessary to change diet if needs are being sufficiently met. Ideal diets contain 50–60% protein, 5–10% carbohydrates and 30–50% fat (Peterson, 2011). Owners can assess the suitability of a diet by observing the nutritional analysis detailed on the packaging.
Feeding of restricted iodine diets has been shown to normalise and maintain T4 levels in most cats, however clinical signs (tachycardia and weight loss) often did not improve, so good clinical control was not achieved (Hui et al, 2015).
Restricted iodine diets leave the entire body in a state of iodine deficiency and currently there are no long-term studies into potential long-term effects of this (AAFP, 2016). There is evidence that dietary iodine is involved in maintenance of healthy immune systems and adrenal function, as well as having antioxidant properties. As with medical management, owners should be aware that these diets do not address the cause of the disease and benign thyroid tumours can continue to grow, increasing risk of malignancy (Peterson, 2011).
Surgical thyroidectomy
A surgical thyroidectomy involves the removal of all, or part of the thyroid gland. Benefits of surgery are numerous and include visualisation of the thyroid tumour (adenoma versus carcinoma) and in many cases surgery can prove curative. Renal function and hypocalcaemia should be monitored closely postoperatively (Birchard, 2006).
Before deciding on the surgical option it is of paramount importance that owners are aware of the advantages and potential complications. As previously mentioned, the possibility of EHTT should be discussed with the use of scintigraphy as a diagnostic aid. Successful communication in these situations can facilitate improved compliance to therapeutic and management plans (McDermott et al, 2015). If owners decide on surgery without scintigraphic evaluation first, they should be aware this may not result in long-term success, should EHTT be present. Effective owner communication such as this can hugely reduce the negative impact that unsuccessful surgery may have if owners have perceived this option as offering a definite cure.
Patients undergoing surgical thyroidectomy should receive treatment prior to surgery so euthyroidism can be established and the anaesthetic profile of the patient improved (Birchard, 2006).
Radioactive iodine (RAI)
Largely regarded as the gold standard in treatment of FH, RAI offers safe and effective treatment and increases success in cats with bilateral thyroid involvement, EHTT and thyroid carcinoma. This method of treatment removes the need for long-term medical management and risks associated with anaesthesia and surgery (Peterson, 2006).
After receiving RAI therapy 95% of cats are expected to be euthyroid after 3 months although improved clinical signs can be evident much sooner. 5% of cats may remain hyperthyroid although this is often attributed to the presence of carcinomas or in rare cases where extremely high T4 values are recorded prior to treatment. Relapse following successful treatment is extremely rare (<5% of cats) and approximately 2.1% of cats will develop long-term hypothyroidism, treatable with daily thyroxine supplementation (Peterson, 2006).
The need for patient isolation is often concerning for owners, but with careful unit design and appropriate enrichment these issues can be addressed and concerns minimalised (Figures 3 and 4).
Benefits of treatment may be considered to out-weigh negative aspects of short-term owner–cat separation. Current statistics on success rates and all potential complications must be discussed fully with owners so informed decisions can be made.
Discussing the options
With so many treatment options available the importance of effective owner communication is again highlighted. Communicating with owners is the only way to ascertain both theirs and their pet's emotional and physical needs (Hedberg, 2016). Treatments plans depend on many factors and there is no standard protocol that can be used. Considerations include the cat's temperament, owner's ability and/or commitment to daily medicating, cost and availability of treatment. From a clinical viewpoint the presence of EHTT and/or concurrent disease processes should influence treatment plans.
Hedberg (2016) discusses the 7 Cs of communication and the importance of each can be linked to owner discussions regarding FH (Table 2).
| Content | Advise the owner on available treatments |
| Context | Information should be relevant to the individual patient |
| Concentrate | Take time to focus on what the client is telling you and ensure the conversation is in a quiet area without interruption |
| Courtesy | Speaking in a pleasant open manner and treating client's decisions and thoughts with respect |
| Consistency | Ensuring the information given to clients is consistent, regardless of which staff member is delivering it. If you are unsure about a particular topic, it may be best to refer the client to someone else |
| Compassion | Be sympathetic to the owner's needs and concerns |
| Conclusion | Practice the art of communication and seek advice where needed |
Communicating with owners allows effective management of outpatient care. By improving communication, improved communication is often seen from the owner (Hedberg, 2016). This ensures better compliance with treatment regimens, and greater customer satisfaction due to a reduction in anxiety and stress (Hedberg, 2016).
Conclusion
Communication is a vital part of helping owners to understand FH as a condition and how it may affect their cat. Owners should be aware of the diagnostic process and the importance of detecting concurrent disease and/or EHTT. Treatment options should be openly discussed and owners assisted in making decisions they are happy with and feel fully informed to make. Potential complications that can arise following treatment should be deliberated prior to commencement, not after issues arise. By ensuring owners are informed and supported RVNs can increase owner satisfaction and compliance and improve the quality of care their patients receive.