PPID stands for Pars Pituitary Intermedia Dysfunction. It is the correct veterinary term for what is commonly referred to as equine Cushing’s disease. Over the last few decades, our understanding of PPID has progressed substantially. However, there are still aspects that we have yet to fully understand. Ongoing worldwide research on the topic is trying to fill in the gaps so that we can diagnose PPID earlier and manage it more effectively.
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What happens in PPID?
Time for a bit of biology! The brain is a complex structure with many working parts which all have to communicate with each other correctly in order for the body to function as it should. There is a region called the hypothalamus which can be thought of as a control centre. The hypothalamus regulates many essential processes including endocrine (hormone) function, it sends signals to its neighbour, the pituitary gland, which then releases the hormones that set in motion these pathways.
The hypothalamus also has nerves that connect it to the pituitary gland. These nerves release a substance called dopamine which acts to prevent the pituitary gland from being over-active. Basically, they keep the gland in check.
In horses that have PPID these nerves are damaged meaning that the pituitary gland isn’t inhibited by dopamine. It’s a gradual process thought to be caused by age-related damage to the nerves, which leads to overactivity of the pituitary gland and excess production of the hormones it secretes.
How do I know if my horse or pony has PPID?
As mentioned, PPID is believed to be brought about by age-related change. This is why it’s commonly seen in older or geriatric horses, generally above 15 years. Many horse owners are aware of the typical curly-coated appearance of affected horses and it’s a good sign to look out for. What’s actually going on is that abnormal pituitary gland function causes dysregulation (loss of control) of the normal seasonal hair growth patterns, as a result the hairs are being held on to instead of being shed appropriately.
The disease can also cause subtle signs such as weight gain or fat accumulation, often appreciated as a cresty neck, and muscle weakness which can create a pot-bellied appearance. Many horses will be more thirsty than normal and urinate more frequently, they may be more susceptible to skin infections, intestinal parasites or dental disease, and occasionally some will have neurological signs or changes in behaviour.
Importantly, equines with PPID will often have laminitis
Recent evidence has shown that in PPID there is often a long phase where laminitis is present but not causing a problem to the horse, although it may be suspected from divergent lines on the hooves. As it is the one sign of PPID that can have a serious impact on the horse or pony’s quality of life it’s important to look out for early warning signs of laminitis. Laminitis is a whole other topic in itself, but the laminitis seen with PPID and equine metabolic syndrome (EMS) is a bit different to that seen with pasture or stress related induced laminitis. Catching PPID before bouts of painful laminitis occur can help prevent the often chronic relentless cycles of laminitis that can occur from other causes.
If you see the signs of PPID then it’s a good idea to get your vet out to do a check up, or it may be that they recommend testing for the disease at a routine check or dental appointment based on your horse’s appearance or history.
Testing for PPID
The first line of testing is often an ACTH (adrenocorticotrophin hormone) test through a blood sample. This may be done with or without a full haematology and biochemistry panel to check your horse’s general state of health. ACTH is one of the hormones secreted by the pituitary gland. In PPID horses and ponies, it is present at blood concentrations higher than normal because of the dysregulated activity of the gland.
However, as mentioned the disease is gradual in onset so sometimes horses that have early PPID won’t have levels above normal. Either repeat testing in the future, or additional tests are needed to confirm the disease. This is also an important topic of current research.
How is PPID treated?
The mainstay of treatment is a drug called pergolide which is given by mouth each day. Often a higher dose is given initially to control the signs, which can take several months. Sometimes it can be reduced, but lifelong treatment will be needed. Good management of horses and ponies with PPID includes clipping the excess hair to prevent sweating and daily grooming to keep the horse clean. Gentle regular exercise is also beneficial in those that do not show signs of laminitis.
If the horse already presents with signs of laminitis this will require appropriate control depending on the degree. This often means remedial shoeing or trimming. An appropriate diet is also important, with limited or no access to pasture and careful stable management with clean thick bedding. Additionally, it is a good idea to have these horses and ponies with PPID checked for EMS. This can produce some similar signs such as laminitis and weight gain, and unchecked EMS can prevent good control of laminitis in equines with PPID.
What does PPID mean for my horse?
Horses and ponies with uncomplicated PPID generally have a good prognosis. With appropriate treatment and management, signs should improve. Repeat ACTH testing after starting therapy should show a reduction in blood concentration.
We are slowly becoming more aware of the true number of horses and ponies affected by PPID. But it remains an underdiagnosed condition, largely because it’s easy to put the signs down to normal age-related changes. Often veterinary care isn’t sought until signs are severe or laminitis has developed. These are often the more difficult cases to manage.
It’s important to be in tune with your older horse and recognise that although he might be showing some changes because of his age, it might be that PPID is behind them. If you have any doubts then discuss with your vet at his next scheduled check-up or book him for peace of mind.
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