What is PPID and how is it treated in horses?

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

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.