EQUINE CUSHING’S DISEASE MAEGAN GOSSETT

WHAT IS EQUINE CUSHING’S DISEASE?  Equine Cushing’s Disease or Equine Pituitary Pars Intermedia Dysfunction is where there are problems with certain glands in the brain that release hormones.  Because of the knowledge we have now of Equine Cushing’s Disease, it is now referred to as Equine Pituitary Pars Intermedia Dysfunction or PPID.  It is called PPID because it is said that a gland in the brain, the pituitary pars intermedia, is the source of the problem.  The problem can be hypertrophy (excessive growth in size of cells), hyperplasia (excessive growth in size due to cell production), and microadenoma (small tumor) or macroadenoma (large tumor).

CAN YOUR HORSE GET PPID?  Any horse can acquire this disease, horses older than 15 years are more prone.  With more knowledge in equine veterinary medicine, there are more older horses in this generation than there ever has been. With a bigger information base and horse owner understanding, awareness is heightened on taking care of the older horse and diseases related to age.  It is not contagious!  This disease is a metabolic disease, the body does this on it’s own.

CLINICAL SIGNS: WHAT TO LOOK FOR  Most common clinical signs your horse would show is:  Hirsutism  Laminitis  Muscle atrophy  Fat accumulation  Polydipsia  Polyuria  Lethargy

HIRSUTISM  Hirsutism is an abnormally long, curly hair coat year round.  This is the most common clinical sign of this disease.

LAMINITIS  Laminitis is a scary word in the equine industry, and a horse that has PPID can get laminitis.  Laminitis is secondary to this disease and is reported in 24%-82% of cases that are diagnosed.  What is Laminitis?  It simply means, inflammation of the lamina or the tissue inside of the hoof wall.  When the lamina gets inflamed or mad, it starts to detach itself from the hoof wall.  The detachment aids in the rotation of the coffin bone, as well as, the sinking of the coffin bone.  While the coffin bone is detaching, the flexor tendon is continuously pulling on the coffin bone. This tendon helps with the flexion of the coffin bone when the horse walks.

EQUINE FOOT: NORMAL AND LAMINITIC The picture on the left shows how a normal equine foot should be, and the picture on the right shows of what laminitis does to the foot mechanically.

EQUINE FOOT RADIOGRAPHS The image on the left shows a normal equine foot, and the image on the right shows significant rotation of the coffin bone and angles measured of the rotation.

LAMINITIS  A horse going through laminitis will show signs of extreme pain.  The horse on the right is showing signs of foot pain; the back feet are tucked underneath the horse and the horse is leaning backwards off the front feet.  There are ways to deal with the foot and to help with the rotation of the coffin bone.  No one knows exactly why horses with PPID get laminitis secondary to the disease.

MUSCLE ATROPHY AND WEIGHT LOSS  Weight loss caused by muscle atrophy can be the earliest signs of PPID.  Muscle atrophy is a loss of muscle mass.  Most older horses can have weight loss due to other issues, but be careful not to confuse age with weight loss and thinking nothing is going on.  The horse on the left shows a potbelly appearance.

FAT ACCUMULATION  PPID horses can often get fat accumulations on their body, specifically in areas on the crest of the neck, the tail base, the sheath, and the supraorbital fossa.  The horse on the right has fat accumulated on it’s neck.  These signs are also observed in Equine Metabolic Syndrome, and some PPID horses have been misdiagnosed because of the similar clinical signs.

FAT ACCUMULATION IN PPID HORSES The picture on the left shows areas where horses deposits fat and the horse on the right has fat in the supraorbital fossa (above the eye).

POLYURIA, POLYDIPSIA, AND LETHARGY  Polyuria mean urinating frequently, and polydipsia mean drinking a lot.  There are multiple reasons why a PPID horse would have these clinical signs.  Lethargy means a lack of energy and enthusiasm.  Horses with PPID are not as energetic, and have a dull attitude.

DIAGNOSING  Diagnosing PPID is important because this disease if life-threatening and common.  There are multiple ways to test for PPID:  ACTH plasma levels.  Dexamethasone suppression test.  TRH stimulation test.

TREATMENTS  Treating of PPID focuses on improving overall health and to reduce risks of secondary diseases: laminitis and immunosuppression.  Management practices are a good way to start: using a pelleted feed for senior horses, dental and hoof care, and deworming practices put into place.  Body clipping horses with hirsutism during the warm months helps to prevent/limit hyperhidrosis and avoid hyperthermia.

TREATMENTS (CONT)  The current and most used pharmaceutical drug on the market that helps horses with PPID is called Pergolide.  Pergolide is a dopamine agonist that helps with the chemical imbalance in the brain.  Prascend is the brand name of pergolide, and PPID horses will be on 1 tablet, by mouth, once a day for the rest of their life.  Once treatment has started, regular blood tests should be done annually or even twice yearly to make sure the dose of medication is correct.

 PPID is a manageable disease once diagnosed and treated appropriately.  The secondary issues to the disease are also manageable and treatable.  If you suspect that your horse could have this disease, please call your local veterinarian and they can speak with you more about PPID.

REFERENCES  Smith, B. (2009). Endocrine and Metabolic Diseases. In Large Animal Internal Medicine (4th ed., pp ). St. Louis, Mo.: Mosby Elsevier.