Formerly known as equine Cushing’s disease, pituitary pars intermedia dysfunction (PPID) is now the fifth most commonly recognised syndrome by horse owners in the UK, which has been helped by improved awareness and better diagnostic testing.
PPID affects the pituitary gland, which is located at the base of the brain, and is normally regulated by a substance called dopamine and produces a variety of hormones. In horses with PPID, the pituitary gland doesn’t produce enough dopamine. This means that the gland is unregulated and produces too many hormones, and the signs of PPID are associated with these elevated hormone levels.
Who is at risk?
PPID is associated with ageing – compared with a 10-year-old horse, a horse of 15–20 years is three times more likely to have PPID and a horse of 20–25 is six times more likely. It has been seen in horses under 10 years old, but this is rare. All breeds and types of equines can develop PPID.
Look out for the signs
The onset of PPID is gradual, and the early signs are often difficult to spot and are commonly attributed to old age, but you may start to recognise one or more of the classic signs, which include…
- an abnormal coat, ranging from mild changes in shedding or colour during the early stages through to a curly, overgrown coat in the later stages
- abnormal fat distribution, including fat pads around the eyes
- loss of muscle condition, with a pot belly and wasted topline
- excessive, patchy sweating
- increased drinking and urination
- lethargy and depression
- poor performance
- recurrent infections, such as hoof abscesses and sinusitis
PPID isn’t curable, but it’s treatable and can be managed. There’s only one veterinary medicine licensed for the treatment of the signs associated with PPID, called pergolide. This drug helps to normalise hormone secretion from the pituitary gland into the bloodstream.
Because the treatment affects hormone production, there’s usually a short lag between beginning treatment and seeing an improvement in the signs. It’s usually 6–12 weeks before you can see a difference and coat changes often take the longest to improve, as these only become apparent when your horse next sheds his coat.
Unfortunately, although pergolide will improve the signs of PPID by normalising your horse’s hormone levels, it won’t stop the progression of the disease. This means that he may go on to develop new or recurrent signs of PPID and this is usually an indication that the dose needs adjusting. The rate of progression is poorly understood and it varies widely between horses who are affected. Your vet will start your horse on the lowest possible dose, then monitor his progress.
After treatment has started, your vet will take another blood test to measure your horse’s response to treatment. Typically this is performed every 4–6 weeks until the levels of ACTH in his bloodstream normalise. This gives the best indication that an improvement in signs will follow. If the blood test shows that
the ACTH levels are still elevated, your vet may recommend altering the dose.
Once your horse’s ACTH levels have normalised and the PPID is under control, it’s recommended that blood tests to monitor ACTH levels should be carried out at least twice a year to ensure the current dose of pergolide is correct. Checking your horse’s ACTH levels every six months means that your vet can pick up any early indicators of PPID progression in your horse and take action to regain control of the disease.
It’s recommended that one monitoring blood test is performed in August or September, because the pituitary gland is more active in horses during the autumn months and it’s thought that there’s an increased risk of developing signs during this period. A second routine test should then be performed in spring.
As well as blood testing, it’s important to be vigilant and monitor your horse closely for any changes in his signs or developments of new ones. Laminitis is potentially the most damaging of all of the signs that may develop as a result of PPID. Bouts of laminitis can occur intermittently and without warning, so it’s very important that risk factors for laminitis, such as PPID and weight gain, are controlled. As well as managing your horse carefully day to day, regular monitoring of his ACTH levels and adjusting treatment appropriately will reduce the risk of laminitis.
A team effort between you and your vet is the best way to monitor your horse, and ensure that his PPID is kept under control and that he leads a happy and normal life.
Find out more about PPID and how best to manage it in the September issue of Horse&Rider, on sale 27 July 2017.