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Cushing's Disease (PPID)

 The pituitary gland is a small gray gland attached to the base of the brain. It is often referred to as the master gland of the body, since the hormones it secretes regulate many body processes, including TSH, a thyrotropic hormone which regulates the thyroid and ACTH (Adrenocorticotrophic hormone) which regulates the adrenal glands. Cushing's disease is caused by a benign tumor or an enlargement of the pars intermedia of the pituitary gland. A more accurate term for this condition is pituitary pars intermedia dysfunction  (PPID).  The increased levels of ACTH caused by the tumor or enlargement of the pars intermedia in turn cause the adrenal glands to produce more cortisol. Many of the symptoms of PPID are directly & indirectly  caused by the increased cortisol levels. Cortisol induces insulin resistance (IR) as well.


Common symptoms of PPID are:
  • Sudden-onset polydipsia. An affected horse may drink as much as 80 liters of water a day (as opposed to an average 20 – 30 liters). This is accompanied by frequent urination
  • Abnormal hair growth and shedding. Affected horses may develop a growth of heavy, coarse, often curly hair, which does not shed in the summer. This is usually accompanied by sweating
  • Development of a swayback stance and a pot belly
  • Filling above the eyes caused by the deposition of fat
  • A general appearance of malaise, depression, with dull eyes and drab coat
  • Increased appetite (usually with no accompanying weight gain)
  • Chronic laminitis (inflammation of the lamina of the hooves, can cause coffin bone to rotate, commonly referred to as founder)
  • Loss of muscle over the topline
  • Compromised immune system. This makes the horse susceptible to a myriad of conditions/diseases which are often passed off as old age. These include respiratory disease, skin infections, abscesses of the foot, buccal ulcers, and periodontal disease
  • Unfortunately, often one of the first symptoms of early PPID before any of those listed above, is unexplained fall laminitis


Diagnosing PPID
There are several tests used for diagnosing PPID, but the two most common ones are the dexamethasone suppression test and the ACTH assay. Unfortunately, the dexamethasone suppression test requires the administration of the synthetic corticosteroid dexamethasone which can precipitate laminitis in a PPID horse.

The ACTH assay is the one recommended by the Equine Cushings list and to date is the safest & most accurate test for PPID. 

The ACTH blood draw does require special handling but there is no risk to the horse & the ACTH level can then be used as a guideline for adjustment of pergolide dosage. However, one must also keep in mind the seasonal ACTH high which generally starts in September & normalizes in January.

One of the biggest problems  with PPID and IR is misdiagnosis. PPID & IR share many of the same symptoms & consequently many veterinarians confuse PPID wth IR and vice versa. While the more advanced cases of PPID often develop IR, the two don't necessarily go hand in hand and treatment is most certainly not the same.
PPID is controlled with medication and IR is managed by diet.
As a precautionary measure I feel it is wise to put any PPID horse on an IR diet, but an IR horse (who does not have PPID) should not be treated with pergolide.
Common medications for PPID are:
Cyproheptadine (Periactin) and  Pergolide Mesylate (Permax).
Cyproheptadine has taken a back seat to pergolide in the treatment of PPID.  It can be effective for awhile but then loses effectiveness.

Back in 2000, my PPID mare Tamera developed laminitis while on Cypro, once we started her on pergolide she never came down with laminitis again.
Pergolide is far superior in managing the symptoms of cushings.

[In 2007, the FDA withdrew pergolide from the human market in the US & Canada because of concerns over heart valve fibrosis & lung fibrosis. However, as far as we know this has not been seen in horses]

In 2000, Dr. Kellon  published the first trial with the herb chastetree berry (vitex agnus castus) & it seemed to have positive results in many horses at least for awhile, especially with shedding patterns. However to date, there is no proof that Vitex lowers ACTH levels & ultimately these horses will eventually need pergolide.

Below are photos of Tamera my PPID/IR mare prior to be being treated with pergolide & then while on pergolide.



Managing Cushing's
  • Avoiding stressing the horse. The hormonal profile of many horses with Cushing’s already indicates high stress levels, so reducing stress is critical
  • Providing a safe, comfortable “sanctuary” for the horse
  • Sticking to a strict routine, which will help minimize stress
  • Keeping water and feed conveniently located and in the same place
  • Clipping the horse in warm weather; using blankets when it is cold
  • Keeping up grooming to minimize skin diseases
  • Maintaining good hoofcare
  • Checking teeth regularly and having them checked by a professional twice a year
  • Avoiding turning the horse out with aggressive horses
  • Avoiding contact with horses from a new location
  • Keeping immunizations to a minimum/ making sure all necessary shots are given
  • Deworming regularly
  • Providing an appropriate diet for the horse. This usually involves elimination of simple carbohydrates
As we have seen time & time again on the Equine Cushings list when managed properly horses with this diagnosis can have long, full & active lives.
Tamera in March of 2007
On June 2, 2007 our beloved 31 year-old Tamera was euthanized due to anhydrosis (the inability to sweat).
She had suffered from this condition for several years, but surviving one more AZ summer was not in the cards for my sweet girl. She passed peacefully and with dignity surrounded by her loving family. I will be forever grateful for the time we had together and all that she taught me.

                 


****A Final note: If you have a horse that you feel may have PPID the best advice I can give you is to join the Equine Cushings list for immediate help, & then when you can, take Dr. Kellon's Cushings & Insulin Resistance Course.


References

http://pets.groups.yahoo.com/group/EquineCushings/

Cushings & Insulin Resistance Course by Dr. Eleanor Kellon, March 2008







May 2, 2009