32 | How to easily and confidently treat and nurse dogs with Cushing's disease

PodcastEndocrine
Written By Laura Jones

Cushing’s disease is one of the most common endocrine diseases we see in dogs.

 

We sometimes even see it in cats, and nurses are heavily involved in investigating and treating these patients. So what is Cushing’s disease, and how do we treat and care for these patients? Let’s find out…

What is Cushing’s disease?

Cushing’s disease, or hyperadrenocorticism, is characterised by the hypersecretion of cortisol from the adrenal glands.

There are two causes of hyperadrenocorticism: pituitary-dependent or adrenal-dependent.

Let’s start with Pituitary-dependent Disease.

Pituitary-dependent hyperadrenocorticism, aka PDH, is the most common form of Cushing’s disease, accounting for around 80-85% of cases. 

These patients have a functional benign tumour on their pituitary gland secreting excessive ACTH.

The ACTH continually released from the tumour cells stimulates both adrenal glands to release cortisol. As the tumour continues to release ACTH, it bypasses the negative feedback system - the body’s usual way of shutting off ACTH release to maintain a normal cortisol level.

As a result, both adrenal glands continue to be overstimulated and release cortisol, and both glands increase in size.

What about adrenal-dependent disease?

Patients with adrenal-dependent hyperadrenocorticism have a functional adrenal tumour on one of the adrenal glands. This tumour secretes cortisol, causing circulating cortisol levels to rise.

The increased cortisol levels will activate the negative feedback system on the hypothalamic-pituitary-adrenal axis, shutting off the release of ACTH from the pituitary gland to try and keep cortisol levels normal.

However, this means that the normal adrenal gland without the tumour receives no stimulation since it still needs ACTH, so this gland begins to atrophy.

The result is a patient who has one adrenal gland with a tumour and one small adrenal gland.

Which patients get Cushing’s disease?

Hyperadrenocorticism is primarily seen in dogs. It’s also seen in cats, though very, very rarely. It’s usually seen more commonly in middle-aged to older dogs, and poodles, dachshunds, terrier breeds and Boxers are predisposed.

Functional adrenal tumours are more commonly seen in female dogs than in male dogs.

What signs do we see in a Cushingoid patient?

The signs we see in patients with Cushing’s disease are associated with glucocorticoid excess. They include:

  • PU/PD and polyphagia

  • Weight gain

  • Pot-bellied appearance

  • Excessive panting

  • Bilateral, symmetrical hair loss on trunk

  • +/- calcinosis cutis (less common)

  • +/- facial paralysis (less common)

  • Fragile skin (especially in cats)

So you suspect your patient has Cushing’s. How are they diagnosed?

Hyperadrenocorticism is usually diagnosed using a combination of bloodwork, urine analysis and endocrine function testing. Occasionally, we may also perform diagnostic imaging - for example, a head CT to look for a functional pituitary tumour or an abdominal ultrasound to look for an adrenal tumour.

Let’s start by looking at biochemistry and haematology…

On biochemistry, ALKP/ALP (alkaline phosphatase) increases are commonly seen. Mild fasting hyperglycaemia (in 5-10% of dogs; 80% of cats) can also be seen, and on haematology, a stress leukogram (neutrophilia, monocytosis, lymphopenia and eosinopenia) may be seen due to the excessive steroid levels.

And then there’s urine analysis

Urine analysis reveals a low USG of <1.020 in most patients. Around 5-10% of cases also have glucosuria, and around 50% of cases also have proteinuria.

Urinary tract infections are also more common in patients with Cushing’s disease, due to the immunosuppressive effects of excessive steroid levels -> however, most patients do not have clinical signs of a UTI.

How do we actually diagnose Cushing’s disease?

There are 3 tests typically used to rule Cushing’s disease in or out. They are the urine cortisol: creatinine ratio (UCCR), the ACTH stimulation test, and the low-dose dexamethasone suppression test (LDDST).

Let’s look at the urine cortisol: creatinine ratio 

The UCCR is a rapid, non-invasive screening test. It’s a highly sensitive test, meaning it rules out the disease, but it’s not very specific, so it can’t definitively rule it in.

A high UCCR does not confirm a diagnosis of hyperadrenocorticism. It instead indicates further diagnostic tests are required, such as an ACTH stimulation test or low-dose dex suppression test.

What about the ACTH stimulation test?

The ACTH stim test evaluates the adrenal gland’s function in response to synthetic ACTH administration. It’s used most commonly to differentiate between iatrogenic and spontaneous disease.

The test is performed by measuring baseline cortisol levels and administering synthetic ACTH before repeating the sample an hour later.

An exaggerated response to ACTH is seen in patients with Cushing’s disease. However, in challenging-to-diagnose cases, we often perform an LDDST.

What is the low-dose dexamethasone suppression test?

An LDDST evaluates the negative feedback loop of the hypothalamus -> pituitary gland -> adrenal gland axis.

It’s performed by collecting a baseline serum cortisol sample, injecting a low dose of dexamethasone IV, and then repeating those samples 4 and 8 hours post-injection.

In dogs that don’t have Cushing’s disease, dexamethasone activates the negative feedback loop, suppressing cortisol levels and causing a lower result. However, in dogs with Cushing’s, dexamethasone cannot suppress the cortisol released, so levels remain elevated.

What other tests might we perform?

Once you’ve diagnosed your patient with Cushing’s disease, additional tests might be required to confirm the location of the disease - i.e., whether it is pituitary or adrenal-dependent disease. These tests include an abdominal ultrasound to look for an adrenal mass, a CT or MRI of the head to look for a pituitary mass, or endogenous ACTH levels to see how much ACTH the patient is producing.

So that’s your patient diagnosed. How will we treat them?

The treatment option we select depends on the type of adrenal disease present.

Patients with pituitary-dependent disease require medical treatment with trilostane (Vetoryl). This drug selectively inhibits the synthesis of adrenal cortex hormones. Treatment is measured with either repeat ACTH stimulation tests or pre-pill cortisol testing.

ACTH Stimulation Tests

ACTH stimulation tests are performed to monitor response to treatment in exactly the same way they are during diagnosis. They must be performed 4-6 hours after the medication is given.

Pre-Pill Cortisol Testing

Pre-pill cortisol testing is a newer method of assessing response to treatment with trilostane. It’s a suitable option for clinically well patients who are calm - if they’re significantly stressed or unwell on the morning of sampling, the test can’t be performed.

The test is performed by measuring cortisol levels immediately before administration of trilostane.

What about patients with adrenal-dependent disease?

In patients with adrenal-dependent hyperadrenocorticism, surgical management is usually the treatment of choice.

In cats with Cushing’s disease, medical treatment is often challenging and less successful, and generally, adrenalectomy is performed.

So how do we nurse these patients?

Normally, our cushingoid patients aren’t in the hospital for long. They’re usually in having diagnostics, but otherwise, they tend to be clinically well and don’t generally require inpatient supportive care.

However, there are a few things to be aware of when nursing these patients.

Firstly, they often have thin and fragile skin, meaning we need to be careful with things like clipping, and application of tape and dressings.

They can also get muscle stiffness and weakness due to a complication called Cushing’s myopathy, so mobility support is really important for these patients.

Like any chronic disease, client education is also important. Our goals of long-term nursing care are to maintain or improve quality of life whilst minimising clinical signs and adverse effects of medication or the patient’s disease.

Regular reassessment, updated history collection and clinical scoring are indicated to measure the patient’s response to treatment. Cushing’s clinical scoring sheets can be used, which I’ll link to in the description below this episode.

When chatting to your cushingoid pet parents, or seeing these pets for a pre-pill cortisol sample, ask them about their pet’s:

  • Appetite

  • Thirst

  • Urination

  • Defecation

  • Panting

  • Frequency and timing of last medications

  • Behavioural or other health changes

And pass that information on to your vet, alongside the results of the diagnostics you’ve performed.

The importance of having a dedicated nurse involved in the ongoing care of these patients should not be overlooked. That way, you can get to know the patient and their family, help pick up on subtle changes early, and ultimately improve treatment compliance and quality of life.

So there you have it - an overview of how we diagnose, treat and care for patients with Cushing’s disease. 

Though they might not be hospitalised for long, we still make a huge difference in the care of these patients - and things like careful handling, minimising stress during sampling, and long-term client education and support are important areas of nursing care. 

We see these patients very commonly in practice, and if you’re not already involved in the ongoing care of these patients - now’s the time to start! It’ll make a huge difference to your patients and clients and provide you with more job satisfaction, too.

Did you enjoy this episode? If so, I’d love to hear what you thought - screenshot it and tag me on Instagram (@vetinternalmedicinenursing) so I can give you a shout-out and share it with a colleague who’d find it helpful!

Thanks for learning with me this week, and I’ll see you next time!

References and Further Reading

Laura Jones
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