Sparky is a 10-year-old Maltese-Cross who looks a lot cheekier than he is. He's a bit of a nervous soul, but a great patient - never complaining and very patient with all the fuss and the numerous vet visits. His predicament kicked off in January when his owner reported that he had been ravenous and drinking a lot of water. He also appeared to be developing what looked like a pot-belly.
From the vet side of the examination table, this reads like a textbook case! This must be Cushing’s Disease (Hyperadrenocorticism).
The Disease - Hyperadrenocorticism
Cushing’s Disease is a syndrome seen in middle-aged to older dogs whereby a tumour either on the pituitary gland in the brain or on the adrenal gland itself leads to an over-production of cortisol. 85% of dogs have the pituitary-dependent cause. In some cases, the pituitary tumours can get so big that dogs can start showing neurological signs associated with a brain tumour!
Sparky’s initial blood chemistry test (8 January) gave us some clues that strongly hinted at Cushing’s:
Values to note:
● High liver enzymes
● High cholesterol
A urine sample was also collected and showed that his urine was very dilute: 1.008 (normal should be above 1.030).
Dilute urine often accompanies increased drinking, though can be present with a multitude of other disease processes, including UTIs (urinary tract infections). Up to half of Cushingoid dogs can have a UTI, including subclinical infections that do not show up on routine urinalyses in clinic.
We needed to perform a test to confirm our suspicions. Sparky had an ACTH stimulation test performed in the clinic. ACTH (Adrenocorticotropic hormone) is the signal hormone released by the pituitary gland in the brain that stimulates the adrenal glands to produce cortisol.
Sparky nailed his test (18 January) showing a massive cortisol spike consistent with Cushing’s disease:
Sparky had an ultrasound of his abdomen performed to check for tumours in his abdomen which would suggest the rarer diagnosis of a tumour on his adrenal gland. This is important to investigate in case surgical removal of a tumour is an option. None was seen in Sparky.
Medical management was started with once daily Vetoryl (Trilostane) capsules.
More testing…more Vetoryl
More than half of dogs with pituitary-dependent tumours will require a dose change… little did we know how many Sparky would require.
A follow-up blood test (30 January) revealed promising news: Sparky’s cortisol levels were within the normal range!
Then we started to lose control!
27 February: high cortisol levels. We increased the Vetoryl dose.
More cortisol testing and more dose changes followed.
We increased the dose another 3 times and were still not able to get Sparky’s levels back into the normal range.
Things started getting weird
Having reached the point where the Vetoryl dose was nearing the upper limit of the acceptable dose range, we started to re-examine the case. Yes, we were making progress, but why was he still not normalising? He was still ravenous and drinking excessively.
As we said earlier, nearly half our Cushing’s patients have a concurrent UTI. We decided to put Sparky on an antibiotic trial to rule out a possible bladder infection. And yet, his owner reported no change in his symptoms.
So, we took a long shot and ran a thyroid test:
Values to note:
● Low T4
● High TSH
The test came back with a low T4 (thyroxine, the active thyroid hormone) and a concomitant high TSH (Thyroid Stimulating Hormone - the negative feedback control hormone produced in the pituitary gland). A confirmatory test!
Most of our hypo (low) thyroid cases are confined to large breed dogs. As seen in Cushing’s, these dogs will usually have thin hair coats as well as poor coat quality. It is very unusual to see in a small dog and even more rare in a dog with concurrent Cushing’s disease.
We added Leventa to his list of daily medications to supplement his thyroid levels.
Where to from here?
Sparky is due back any day for more blood tests. We are eager to see if his symptoms have abated, his cortisol has dropped to normal levels and his thyroid has returned to normal.
Fingers crossed that Sparky gets his spark back soon!
If you notice your older dog is starting to slow down and show some of the above signs, please call the clinic to schedule a consultation.