Ideally, when testing for any disease, it is best to choose a test which is both highly specific and highly sensitive. In practical terms, a test with high sensitivity is good at finding animals with the disease and therefore will produce few false negative results. A test with high specificity gives a positive result in animals that really do have the disease, therefore will produce few false positives.

However, no test for Cushing’s has both high sensitivity and high specificity – all are a compromise between the two. This means the diagnostic tests we have for canine hypercortisolism often have to be used in combination, in order to be confident in the diagnosis.

(Please note - the percentage values provided for sensitivity and specificity below should be considered approximate and are representative of multiple investigative studies on this topic. The author refers the reader to the 2019 Bennaim et al review for further information)

ACTH Stimulation Test (ACTHST)

High specificity (90%), moderate sensitivity (85% PDH and 50% ADH)
False positives are less common. False negatives are fairly common.

Low-Dose Dexamethasone Suppression Test (LDDST)

Moderate specificity (70%), high sensitivity (95%).
False positives are fairly common. False negatives are less common.

Urine Cortisol: Creatinine Ratio (UCCR)

Poor specificity (20%), high sensitivity (97%).
False positives are common. False negatives are less common.

When interpreting any of these tests, it is worth considering the positive and negative predictive value. Positive predictive value (PPV) is the fraction of dogs with a positive test that truly have Cushing’s. Negative predictive value (NPV) is the fraction of dogs with a negative test that are truly free of the condition.

The positive and negative predictive values take both the test and the population being tested into account. If you use a test in two populations with different disease prevalence, the predictive values will be different. Therefore the PPV and the NPV vary depend on how frequently you test.

• If we were to test almost every patient we see (a population with a low prevalence - 5%)

In this scenario, if we use the LDDST we can be 100% sure a negative result is truly negative. However only 16% of positive results will actually have Cushing’s.

• If we were more critical about the patients we test (a population with a high prevelance - 90%)

In this scenario, if we use the LDDST, 62% of negative results will truly be negative and 97% of positive results will have Cushing’s.

Conclusion

The 2012 ACVIM Consensus Statement panel (Behrend et al. 2013) considers the low-dose dexamethasone suppression test (LDDST) as the screening test of choice unless iatrogenic Cushing’s is suspected. Because of the ACTH stimulation test’s lower sensitivity its diagnostic usefulness as a screening test for natural occurring Cushing’s syndrome is inferior to the LDDST'.

However, it is also important to take other factors into account when selecting a diagnostic test, including test availability, cost and concurrent disease present in the patient. It is equally important to improve the potential outcome of the test by ensuring there is a high index of suspicion of disease before confirmatory testing is undertaken.

Please note that the following is a sample protocol created based on literature (Behrend et al, 2013). The exact protocol may vary according to the specific external laboratory, therefore you should check with your regular laboratory before carrying out the test​

1. Collect a basal blood sample*​
2. Inject 0.01 mg/kg i/v of Dexamethasone**​
3. Collect two further blood samples:
   1. 3 - 4 hours later (the consensus statement recommends 4 hours but this will be dependent on the specific laboratory protocol) and
   2. 8 hours later
4. Label sample times clearly on the tubes and request cortisol

Label sample times clearly on the tubes and request cortisol measurement ​​

*Sample type: Suitable sample types at most laboratories include separated heparinised plasma or serum, or centrifuged serum gel tubes​
​
**Note: You should ensure that the dexamethasone product used is licensed for intravenous use

The low-dose dexamethasone suppression test measures the resistance of the pituitary-adrenal axis to suppression by dexamethasone and is interpreted in 2 stages:

• Firstly, the presence or absence of Cushing’s syndrome is determined by examining the 8 hour result. An 8 hour cortisol value greater than 40 nmol/l is generally considered to represent a ‘positive’ result
• Typically in a dog with ADH, the adrenal tumour secretes cortisol autonomously and ACTH production is already suppressed, thus cortisol production is not suppressed in response to dexamethasone administration.

• The second step only applies in the positive cases and checks for evidence of cortisol suppression. In up to 60% of PDH cases, there will be marked suppression of cortisol (to <50% of the baseline value) at either 3 hours or 8 hours providing a way to differentiate between the two types of hypercortisolism.

Please note that the following is a sample protocol created based on literature (Behrend et al, 2013). The exact protocol may vary according to the specific external laboratory, therefore you should check with your regular laboratory before carrying out the test​​

1. Collect a basal blood sample (1-2 ml). Label tube as ‘pre ACTH’​
2. Immediately inject 5 µg/kg synthetic ACTH i.v. or i.m. (Cosacthen)​
3. Collect a second blood sample* (1-2 ml) one-hour post synthetic ACTH (Cosacthen) injection. Label tube as ‘post ACTH’​
4. Submit tubes and request form to the laboratory​​

*Sample type: Suitable sample types at most laboratories include separated heparinised plasma or serum, or centrifuged serum gel tubes

The ACTH stimulation test will identify approximately 85% of cases of pituitary-dependent hypercortisolism.

Dogs with PDH have bilaterally enlarged adrenal glands. With the greater adrenocortical mass, an exaggerated response to ACTH can be expected

The ACTHST will also identify >50% of cases of adrenal-dependent hypercortisolism, as most dogs with ADH will also demonstrate an exaggerated response to ACTH.

However, in some dogs, especially with ADH, there may be atrophy of the normal adrenal tissue and/or the tumour may be insensitive to ACTH. In these cases, as is demonstrated by this video, we can see a ‘flat-line, mid-range’ cortisol response. This explains why the ACTHST is less sensitive for ADH than PDH.

As the sensitivity of the test is less than ideal, especially for dogs with ADH, a diagnosis of Cushing’s should not be ruled out on the basis of a normal ACTH stimulation test result if there is sufficient clinical suspicion.

The ACTH stimulation test will identify approximately 85% of cases of PDH and >50% of cases of ADH.
Therefore the sensitivity of the test is less than ideal, especially in ADH, and some dogs that actually do have hypercortisolism will have normal ACTH stimulation test results. Therefore a diagnosis of Cushing’s should not be ruled out on the basis of a normal ACTH stimulation test result if there is sufficient clinical suspicion.

In these circumstances it is recommended that a LDDST be undertaken in order to try to determine a correct diagnosis. Alternatively, if the clinical signs allow, the patient can be monitored clinically and the ACTHST repeated in 4-6 weeks’ time.

The ACTHST is the only diagnostic test which allows us to differentiate between iatrogenic and spontaneously occurring Cushing’s syndrome. Chronic administration of exogenous glucocorticoid containing treatments, including oral and injectable glucocorticoid medications, topical ear drops and skin preparations, will cause suppression of the hypothalamic, pituitary adrenal axis. This, in turn, will produce a subnormal response to the ACTHST.

The following video illustrates this:

It is vitally important that every monitoring appointment for Vetoryl treated patients uses clinical observations alongside biochemical assessment to decide on the next action for the patient.

Dechra provide a number of tools to aid in the clinical assessment of the patient including the Cushing’s Clinical Score and the CushQOL questionnaire. More information on these can be found in the FAQ section ‘Consultation Support’ below.

If, after clinical assessment, the dog is deemed to be ‘unwell’ (e.g. vomiting/diarrhoea, abdominal pain, off their food), Vetoryl must be stopped, serum electrolytes analysed and an ACTH stimulation test performed using Cosacthen®. The results of the ACTH stimulation test can then help you decide if the dog is unwell due to iatrogenic hypocortisolism (pre- and post-ACTH cortisol <40 nmol/l) or due to another reason (post-ACTH cortisol >40 nmol/l). 

Where any dog becomes unwell whilst receiving any veterinary medicinal product, it is important to report the event to the local body responsible for veterinary pharmacovigilance, even if you are confident the adverse event is not linked to administration of the medicine itself. You can do this directly to your local authority, or alternatively you can provide us with the case details so that we may record the case and forward to local authorities on your behalf. Please use the contact us section of this site. 

For dogs which are not considered clinically unwell, either the ACTH stimulation test or pre-Vetoryl Cortisol (PVC) can be used to monitor cortisol long term. Further information can be found within the treatment & monitoring section of the site.

Since the Pre-Vetoryl Cortisol test does not feature on the Vetoryl Summary of Product Characteristics, informed owner consent for ‘off-label’ monitoring should be obtained.

There is no evidence to suggest that Vetoryl is hepatotoxic

Alkaline phosphatase (ALKP) and alanine aminotransferase (ALT) levels should decrease in dogs on Vetoryl treatment, but may not return to the reference range. In Dechra’s 6 month clinical trial ALT concentrations had decreased significantly by 9-12 days and by 6 months 92% of dogs had levels within the normal range. ALKP concentrations decreased significantly by 4 weeks but at 6 months 58% of dogs still had levels greater than the reference range. 

If liver enzymes are increasing in a dog on Vetoryl treatment this could be due to:

-    Inadequate control of hypercortisolism for the entire 24 hour period 

-    Progression of primary hepatic disease possibly as a result of ‘unmasking’ of an underlying inflammatory hepatopathy due to a reduction in endogenous corticosteroid levels. Vetoryl is contraindicated in primary hepatic disease.

-    Concurrent administration of other medications that may cause an increase in liver enzymes

Further investigations into these possibilities should be undertaken in order to determine the cause of hepatic enzyme increase.

Where any dog experiences an unwanted or unexpected event whilst receiving any veterinary medicinal product, it is important to report the event to the local body responsible for veterinary pharmacovigilance, even if you are confident the adverse event is not linked to administration of the medicine itself. You can do this directly to your local authority, or alternatively you can provide us with the case details so that we may record the case and forward to local authorities on your behalf. Please use the contact us section of this site. 

There is no evidence to suggest that Vetoryl is nephrotoxic.

Urea and creatinine levels can be slightly below the reference range at the time of diagnosis of Cushing’s due to continual urinary loss as a result of glucocorticoid-induced diuresis (cortisol is thought to interfere with antidiuretic hormone (ADH) release or effect, causing polyuria and polydipsia). Therefore, when treatment with Vetoryl is started, urea and creatinine? levels may increase slightly but should remain within the reference range in a dog with normal renal function.

An increase in serum urea and creatinine above the reference range may be pre-renal, renal or post-renal. Determination of the origin of the azotaemia will allow the best next steps for the patient to be identified.  

Vetoryl can potentially induce an iatrogenic hypoadrenocorticism, which induces a pre-renal increase in urea and creatinine due to hypovolaemia. Expected changes to electrolytes include hyperkalaemia and hyponatraemia. Urine specific gravity in these cases may be high.

An azotaemia unaccompanied by hyperkalaemia is more likely to be a primary renal azotaemia. In these cases urine specific gravity should be isosthenuric (1.008-1.012). The Vetoryl datasheet states: “Subclinical renal dysfunction may be unmasked by treatment with the product” and this occurs due a reduction in glucocorticoid-induced diuresis. It is not uncommon for dogs to have both Cushing’s and renal dysfunction. This may simply reflect the fact that both diseases are more common in older dogs. In addition, systemic hypertension occurs in a large percentage of dogs with hypercortisolism. Hypertension may lead to glomerular damage and glomerulosclerosis.

It should be noted that Vetoryl is contra-indicated in dogs with renal insufficiency.

The reason for this is that extrapolation from studies in other species suggest that trilostane is likely to be renally excreted in dogs. Renal insufficiency may impair the excretion of trilostane, leading to increased serum concentrations of trilostane and its active metabolites, which could precipitate adrenal over-suppression.

Further investigations into these possibilities should be undertaken in order to determine the cause of azotaemia. 

Where any dog experiences an unwanted or unexpected event whilst receiving any veterinary medicinal product, it is important to report the event to the local body responsible for veterinary pharmacovigilance, even if you are confident the adverse event is not linked to administration of the medicine itself. You can do this directly to your local authority, or alternatively you can provide us with the case details so that we may record the case and forward to local authorities on your behalf. Please use the contact us section of this site. 

Potassium levels may increase slightly in dogs on Vetoryl treatment, but should remain within reference range. 
 
Some dogs on Vetoryl treatment can have a mild, isolated rise in potassium – the reason for this is uncertain. Therefore, if the dog is clinically well, has normal sodium levels, normal cortisol levels, and the potassium is only mildly elevated then this would not be a cause for undue concern, though clearly it is important to continue to regularly monitor the animal.  

Clinical symptoms of hyperkalaemia are often not displayed unless plasma potassium exceeds 7.5 mEq/L (Maggiore, 2017). However, substantial variation occurs because factors such as the plasma calcium concentration and acid base status can modify the toxicity of hyperkalaemia. Clinical signs that are directly referable to hyperkalaemia include varying degrees of muscular weakness and disturbances in cardiac conduction.

In a study by Wenger (et al 2004) of dogs with PDH treated with trilostane, elevations in potassium concentrations were observed up to a maximum level of 6.2 mmol/l. Using this study as a reference, a persistent hyperkalaemia above this value could therefore raise suspicion of underlying disease which may require further investigation.

If an animal has a persistent hyperkalaemia, and the hyperkalaemia is at a level where there could be adverse consequences, aldosterone levels can be checked pre- and post-ACTH. However, note that in the Wenger (et al 2004) study, there was no correlation between potassium and aldosterone concentrations detected at any of the follow-up evaluations. It would be very rare for an animal to have a normal cortisol level but a low aldosterone level.

- If an animal is hyperkalaemic and the cortisol (+/- aldosterone) monitoring level is low, this may indicate adrenal oversupression, and Vetoryl should be stopped for 7 days. 

- If an animal is hyperkalaemic, the cortisol measurement is normal but the post-ACTH aldosterone level is low, then the Vetoryl dose can be reduced. However, this may result in unacceptable clinical signs of Cushing’s if cortisol levels are inadequately controlled. An alternative treatment for Cushing’s could be considered.

- If an animal is hyperkalaemic and the cortisol and aldosterone measurements are normal, then this could be an idiosyncratic reaction to Vetoryl. If the hyperkalaemia is persistent and is at a level that is causing clinical concern, then Vetoryl should be stopped. An alternative treatment for the Cushing’s should be considered.

There can be other reasons for elevations in potassium, including sampling errors, increased intake of potassium or decreased clearance. Consideration should also be given to this when assessing  hyperkalaemia in these patients.

Where any dog experiences an unwanted or unexpected event whilst receiving any veterinary medicinal product, it is important to report the event to the local body responsible for veterinary pharmacovigilance, even if you are confident the adverse event is not linked to administration of the medicine itself. You can do this directly to your local authority, or alternatively you can provide us with the case details so that we may record the case and forward to local authorities on your behalf. Please use the contact us section of this site. 

Prior to consultation:

• Owners should be encouraged to keep good records at home.  An easy way to ensure this is to direct owner’s to our dedicated website https://www.canine-cushings.co.uk/ where they are able to download a logbook. 
• The consultation itself should be arranged at the time of, or up to 2 hours after, the dog’s normal Vetoryl dosing time (i.e. If the dog is normally dosed at 8 am, the consultation should be arranged between 8 am and 10 am – but the blood sample must be collected before that day’s dose has been administered).
• NB – If a patient is receiving Vetoryl twice daily, and is being monitored prior to the evening dose, then this is the dose that should not have been administered before sampling. The morning dose can be given as per the patient’s regular routine.

During the consultation:

• Questions regarding the clinical signs of Cushing’s should be asked alongside questions which are designed to highlight signs of oversupression or concurrent disease.

For more information please see the FAQ ‘What is the Cushing’s Clinical Score?’ and ‘What is the CushQoL-pet?" in FAQ section - Consultation Support.

• 1 to 2 ml of blood should be collected in a heparin or serum tube for measurement of cortisol.
• We recommend that this sample is sent to an external laboratory participating in an external quality assurance scheme (e.g. ESVE- or SCE- programmes) and preferably that uses a Siemens IMMULITE® – or a method that has been validated against this machine. 

After the consultation:

• Using all information collected, the clinical status of the patient should be determined. The patient will fall into one of three categories, and this determines result interpretation.
  • Clinically well but with signs of Cushing’s
  • Clinically well without signs of Cushing’s
  • Clinically unwell
• We advise that you then use the following flowchart to aid in interpretation of the results:

Since the Pre-Vetoryl Cortisol test does not feature on the Vetoryl Summary of Product Characteristics, informed owner consent for ‘off-label’ monitoring should be obtained.

In this situation, the PVC Flowchart recommends to:

• Re-evaluate case (reassess history and consider Pre-Vetoryl ACTH stimulation test. Contact Dechra Technical Services for further information) AND/OR
• Consider lower dose (use combinations of capsule sizes to decrease the once or twice daily dose)

In this context, ‘re-evaluate case’ means carefully questioning the owner and examining the dog to see if there are any signs consistent with adrenal over-suppression. Questions around lethargy, inappetence and vomiting should be specifically asked to ensure there are no subtle signs of iatrogenic hypocortisolism which the owner has not volunteered. If the owner has kept good home records this process will be much easier. 

If the dog does genuinely appear to be well, then a Pre-Vetoryl ACTH stimulation test can be run. 

If the post-ACTH cortisol is normal (40-200 nmol/l) then the Vetoryl dose could be left unchanged, as these results indicate that (at least at the pre-capsule time) the dog has sufficient adrenal reserve to respond to stressful situations. 

However, a post-ACTH cortisol at the low end of this 40-200 nmol/l range at 24 hours post-capsule, and certainly any dog with a post stimulatory cortisol of <40 nmol/l, would be potentially concerning as it would indicate minimal adrenal recovery at the time the next dose is due. A dose reduction could be a sensible option to reduce the risk of adrenal over-suppression.

In this situation, the PVC Flowchart recommends to:

• Re-evaluate case (contact Dechra Technical Services if further support is required) AND/OR
• Consider dividing the current dose equally between morning and evening doses. If already dosing twice daily then consider a small dose increase (use combinations of capsule sizes to increase the twice daily dose)

In this context, ‘re-evaluate case’ means carefully questioning the owner and examining the dog to see if there are any signs consistent with Cushing’s syndrome. Questions around thirst, urination and appetite should be specifically asked to ensure there are no subtle signs of Cushing’s which the owner has not volunteered. If the owner has kept good home records this process will be much easier. It is worth bearing in mind that it would be unusual for a dog to have persistently elevated circulating cortisol without showing signs associated with this.

Another explanation for an elevated PVC without symptoms of Cushing’s is that the patient was particularly stressed or anxious at the time the sample was taken. 

Once you are happy that the result is a true indication of elevated circulating cortisol, then the recommended next step would be to move to BID dosing. This should be achieved by increasing the total daily dose by up to 50% and dividing into equal morning and evening doses. If the patient is already receiving Vetoryl twice daily, the recommendation would be to make a small increase to the total daily dose. In either case you should re-evaluate the patient after 28 days.

At 4 - 6 hours post-capsule, the aim should be to achieve a post-ACTH cortisol value of >40 nmol/l and <200 nmol/l.

However, it is important to remember that biochemical control should always be matched with clinical control.  It may be the case that a dog is showing no clinical signs of Cushing’s syndrome but has a slightly higher post-ACTH cortisol value (<250 nmol/l).

In this situation, a dose increase would not be required if the clinical signs were well controlled. Therefore, cortisol values should always be interpreted alongside the clinical picture.

Although a post stimulatory cortisol of >200 nmol/l  is higher than we would ultimately like the cortisol to be for a dog on Vetoryl therapy, we do not generally advise a dose increase at 10 days.

Experience suggests that there is likely to be a further reduction in the post-ACTH cortisol at the 28 day test, even if the dose is not increased. Also, we do not want cortisol levels to fall too rapidly. If they do, the animal may suffer from cortisol withdrawal syndrome. Signs of cortisol withdrawal syndrome include weakness, lethargy, anorexia, vomiting and diarrhoea. It should be distinguished from hypoadrenocorticism (Addison’s disease) by an ACTH stimulation test and evaluation of serum electrolytes.

The action to be taken would be dependent on both the clinical signs the dog is displaying and the value of the post stimulatory cortisol. 

Good history taking is essential to determine exactly when the clinical signs are being displayed. This can give an indication as to whether the overall dose of Vetoryl is too low, or whether the effect of Vetoryl is not persisting for the entire 24 hour dosing period.

Where the post stimulatory cortisol is > 120 nmol/l and the preference is to maintain once daily dosing a small increase in the overall dose could be considered. 

Alternatively consideration could be given to moving to twice daily dosing. This can be achieved by taking the total daily dose and dividing equally into morning and evening doses. 

Where a patient is clinically well but there is no response to an ACTH stimulation test our recommendation would be to stop Vetoryl treatment for at least 7 days.

Once the clinical signs of Cushing’s return, Vetoryl can be restarted at a lower dose. The patient should then be rechecked after 10 days (as per SPC recommendations). 

Alternatively, consideration could be given to measuring pre-Vetoryl cortisol (PVC). If the PVC is between 40 and 138 +/- 15% nmol/l then the current dose could be maintained.

Assessment of serum cortisol concentrations alone is unreliable for the monitoring of Cushing’s, therefore paying particular attention to the clinical signs is vital to achieving treatment success. 

To do this, excellent owner communication is vital to truly understand how a dog is doing on Vetoryl. Motivating an owner to take control of their dog’s condition right from the point of diagnosis is of benefit to everyone involved in the dog’s care. Explaining the need for good record keeping at home and providing the tools to enable consistent and effective monitoring can help get owners on board.

As such, Dechra has worked alongside the Royal Veterinary College, London to create the ‘Cushing’s Clinical Score’. This comprises of a series of questions, to be completed by the owner, which can provide you with the information you need in order to determine the true clinical status of your patient. 

The questions cover four factors:

1. Drinking and urination
2. Appetite
3. Demeanour
4. Appearance 

In addition to covering clinical information, the aim is that by using one standardised form throughout the practice, the same questions are asked in the same way for every monitoring consult – ensuring consistency for the patient and owner and improving consult efficiency. 

Click here to download a copy of the Cushing’s Clinical Score to use in your practice.

Click here to hear Professor Stijn Niessen’s overview of the Cushing’s Clinical Score.  

Once an owner has completed the Cushing’s Clinical Score form, a numerical value for the clinical status of the patient will be gained. Lower values indicate better clinical control.

When interpreting the Cushing’s Clinical Score, there isn’t a ‘cut off’ value, or a set score change, which indicates action is required. This is because the score shouldn’t be interpreted as a one off number- but should be monitored over time, in the individual patient.

Each dog will have their own starting score which we would take as their baseline. With treatment we would expect this to reduce (ideally down to 0), and providing the score is reducing or remaining at a constant low level (at which you and owner are happy that the maximum possible clinical improvement has been made) then the dog is doing well.

If, however, the score slowly starts to increase over time, or there is a sudden increase during a routine check-up, this would then warrant further investigation and possible dose adjustment. 

The overall aim of treatment with Vetoryl is to improve the quality-of-life of dogs and, as a result, their owners. Recent research highlighted that it is not just the clinical signs of Cushing’s that impacts on a dog’s quality-of-life. Consideration of specific treatment needs for individual patients as well as their owners are important to optimise the quality-of-life for dogs with Cushing’s.

The scientifically validated CushQoL-pet (Schofield et al, 2019) is a questionnaire which has been developed for completion by pet owners to help assess quality-of-life within your monitoring consultations. It is recommended to complete this at least every three months to facilitate communication and to work with the owner to decide the next steps of their dog’s management.

Click here to download the CushQoL-pet questionnaire for use in your Vetoryl monitoring consultations. 

The possibility of interactions between Vetoryl and other veterinary medicinal products has not been specifically studied. Given that hyperadrenocorticism tends to occur in older dogs, many will be receiving concurrent medication. In clinical studies, no interactions were observed.

Although there is no overt contraindication for use of Vetoryl alongside potassium sparing diuretics, the Vetoryl SPC does state that: The risk of hyperkalaemia developing should be considered if trilostane is used in conjunction with potassium-sparing diuretics. This is because both drugs have an anti-aldosterone effect. 

Vetoryl inhibits aldosterone production by competitive inhibition of the enzyme 3 beta-hydroxysteroid dehydrogenase in the adrenal cortex. Potassium-sparing diuretics competitively inhibit the action of aldosterone, preventing sodium resorption and promoting potassium retention in the distal tubules of the nephrons in the kidney.

Therefore a risk vs benefit analysis for the individual patient should be carried out before commencing concurrent therapy.