What is Cushing's Disease?

What causes Cushing’s Disease?

Cushing's disease, also known as Pituitary Pars Intermedia Dysfunction (PPID), is a complex hormonal disorder that affects horses of all ages. This disease results from dysfunction between the hypothalamus and the pituitary gland. In a healthy horse, the hypothalamus, located at the base of the brain, is in constant communication with the pituitary gland, as it is responsible for regulating the number of hormones produced by the pituitary gland. When a horse develops Cushing’s Disease, this communication is lost, and the pituitary gland begins overproducing adrenocorticotropic hormones (ACTH). The presence of this hormone then leads to the excessive production of cortisol, also known as the “stress hormone.” Excessive amounts of cortisol can result in weakened immunity to infection, insulin resistance, deterioration of muscle, and laminitis.

Symptoms of Cushing’s Disease 

Although it sounds complicated scientifically, many symptoms can lead a horse owner to suspect Cushing’s in their horse. Cushing’s is a progressive disorder, so symptoms may appear early on or as the disease progresses. 

The following symptoms are commonly associated with Cushing’s Disease:

• Lethargy
• Inability to shed coat, increased coat length, or patchy shedding of coat
• Laminitis
• Ligament and tendon inflammation
• Increase in water consumption and urination
• Accumulation of fat in abnormal areas
• Excessive sweating 
• Infertility 
• Recurrent corneal (eye) ulcers

Diagnosing Cushing’s Disease

If you suspect any of these symptoms in your horse, it may be a good idea to seek attention from a veterinarian. Your vet will perform a physical exam and examine your horse’s medical history. To diagnose Cushing’s Disease, your vet may draw blood from your horse and run a series of tests. This may include checking your horse’s baseline plasma cortisol and ACTH concentrations; this requires a simple blood sample that is reviewed by the lab.

A more complex test is the Thyrotropin Releasing Hormone (TRH) Stimulation Test. This test requires a simple blood sample and a second sample after your horse is injected with the thyrotropin hormone. Other tests, which are less commonly used, include Overnight Dexamethasone Suppression Testing and Magnetic Resonance Imaging (MRI). The type of test is typically decided by the vet and based on the symptoms your horse presents.

Treatment and Management of Cushing’s Disease

When a horse is diagnosed with Cushing’s, the first line of treatment is typically Prascend, generically known as pergolide tablets. Prascend is an FDA-approved medication that mimics the action of dopamine to regulate the production of hormones from the pituitary gland. Although this medication does not cure Cushing’s, it can significantly improve the quality of life for a horse with the disease. Once a horse begins to take Prascent, it should be monitored closely by a vet. Blood tests can be repeated to check the internal effects of the mediation. 

Along with taking Prascend, horse owners should pay special attention to their horse’s routine care. The following are particularly important for horses with Cushing’s: 

• Routine hoof care
• Routine dental care
• Routine parasite control
• Low sugar diet while maintaining ideal body weight

As well as Cushing’s medication and routine care, some horse owners turn to additional supplements that further ease their horse’s painful symptoms. Here at Equine, our products are safe for horses with Cushing’s Disease. Products such as Comfort Quik, used to increase joint health and mobility, and Horse Heiro, used to make horses more comfortable and help them get back on grass pasture, can be used (in addition to Cushing’s medication) to improve your horse’s quality of life.