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It’s Just His Age
An article about Cushing’s Disease

Mambo is a ‘cuddly’ 11 year old black Labrador. He has had a few problems through his life and is getting a little stiff now after a very active life. I saw him recently for his annual vaccination and was shocked at the sight of him.

I hadn’t seen him for a few months and as such the change in his appearance was more obvious to me than to his owner. I commented on the changes and his owner said that, yes, she supposed he had changed recently. She reported that he had also slowed down a fair amount but they had put all these subtle changes down to his increasing age.

The changes in his physical appearance could easily have been mistaken for age too and we find this a common occurrence with this particular condition, it comes on so slowly that many owners just believe it to be old- age. He had become pot- bellied and looked bloated and saggy. His hair was thinning too but he wasn’t itchy. He generally appeared what I would call ‘a bit moth- eaten’. He stood panting in front of me and seemed to have aged about 5 years since I had last seen him. On questioning his owners also reported that he had been drinking a fair amount more than usual. His appetite was also very good but in an elderly Labrador this was nothing unusual!

I had very strong suspicions about what might be causing all these things and this was one of the rare times that a ‘text- book’ case came in and presented itself to me. The condition I was almost certain of is called ‘Cushing’s disease’. This is the term that is used to refer to the same condition in humans and is named after the man who first recognised and diagnosed the syndrome. In veterinary medicine we call it by its rather more scientific name of ‘hyperadrenocorticism’ or HAC for short! The break down of the word simply means an over production of steroids by the adrenal glands.

When most people hear the words ‘steroids’ they imagine the body- building steroids we hear so much about in the press. These are anabolic steroids and are quite different to the corticosteroids that are over- produced in HAC. Corticosteroids are essential for life and have a very wide range of functions in the body from helping with certain types of metabolism to dealing with physical and mental stress. They are very important indeed. The opposite condition in which there is a failure to produce them can lead to life- threatening illness and is much more potentially serious than HAC.

In some older dogs the adrenal gland starts to produce way too much of these steroids. Sometimes this is because the adrenal itself becomes enlarged more cells mean more steroids. On other occasions it is because a gland in the brain starts to produce too much of another hormone that falsely tells the adrenals to produce more. Either way, the results are the same.

Anyone who has had high doses of steroids for one reason or another will tell you their effects and they are exactly the same in animals. Your appetite and thirst are stimulated and this makes you drink crave water and food. The steroids suppress your immune system and you can become vulnerable to infections. They weaken muscles and this causes the abdomen wall to become weak and saggy giving animals the pot- bellied appearance. They also affect hair- growth and in animals this usually appears as symmetrical hair- loss down the flanks. In some cases they will also get deposits of calcium in the skin which makes the skin feel gritty. In advanced cases you can get quite nasty skin- infections where the skin has become thin, broken and infected.

Although not particularly life- threatening in the short- term, this condition if left unchecked for a long period of time can cause very serious problems and liver damage.

I needed to be absolutely sure of my diagnosis because the treatment for the disease is extremely specific and it is very dangerous to try to reduce the production of steroids in a healthy dog. As I said before, not enough of these precious things is very dangerous indeed and you don’t want to create this situation with drugs.

I needed to have Mambo in for the day with an empty stomach (much to his disgust!) so I booked him in for the following day for the test. The idea is that you take a blood sample as a baseline to measure the amount of steroids in it. This is usually high but is not enough to be diagnostic alone because some dogs with HAC may be normal at certain times. As soon as we have the blood we injected a very low dose of steroids into the blood stream according to his weight. We then take blood samples after 4 hours and 8 hours.

This is called a low- dose dexamethasone suppression test. It sounds very fancy and complicated but the theory is fairly simple. In a normal dog when you give steroids from outside the body there is a feed- back mechanism. The body registers that there is an unexpected rise in the amount of steroid in the blood stream and tells the body to produce less of its own to compensate for this and keep everything as it should be. In a dog with HAC this cannot happen and the levels of steroids that you measure later are much higher than they should be because the suppression has not happened.

We sent the samples away for testing and gave Mambo a much- appreciated and very belated breakfast and sent him home. We had the results faxed back the next day and it was little surprise that our suspicions were confirmed.

We ordered the drug we needed in for the following day and calculated the dose Mambo needed. You do need to monitor them to start with to ensure you’re not overdoing things but thankfully now we have a much safer drug available than previously and side effects are much less common.

In a few weeks time Mambo should be feeling much more normal, although I doubt that appetite will change much!

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