Equine Cushing’s disease or Pituitary Pars Intermedia Dysfunction (PPID) is caused by hyperplasia (enlargement) or adenoma (benign tumor) formation in the pars intermedia portion of the pituitary gland at the base of the brain. It is a problem primarily of horses over 18 years of age but may develop in pre-teen or teenage horses, especially those that tend to obesity. PPID causes endocrine imbalances that interfere with health and quality of life.
One tell-tale sign of advanced Cushing’s disease is the long, shaggy hair coat (hirsutism) that fails to shed even in the face of long days and summer weather. A horse with PPID displays other peculiar physical characteristics: A pot-bellied shape and diminished muscle mass along with abnormal fat distribution of a swollen prepuce, a cresty neck, and puffiness around the orbits of the eyes. These characteristics occur as a progressive change over years. Subtle changes in the beginning stages may be less obvious: Sweating in odd areas; lethargy; and irregular and delayed shedding. Testing of blood samples for endocrine abnormalities is the best means of identifying suspect cases and to corroborate clinical signs with laboratory evaluation of specific hormones. The thyrotropin-releasing hormone (TRH) stimulation test yields a strong degree of confidence in diagnosing a horse as having PPID.
PPID is not a disease that can be cured since it is caused by an enlargement or benign tumor development in the pituitary gland that isn’t able to return to normal size or structure. The objective for treatment is to slow progression of the disease and to mitigate adverse clinical signs associated with loss of dopamine neurotransmitter concentrations. Life expectancy may be improved a bit, but the most important goal is to improve an affected horse’s quality of life through diligent management and treatment. Conscientious health care is an important part of management, including preventive vaccines, deworming, and dental care. Pergolide, given daily as an oral medication has excellent success in managing PPID.
Cushing’s disease, a common malady of the pituitary gland of elderly horses, is not a health issue that is preventable through management. Early recognition makes it possible to slow its progression. Have your veterinarian assess your horse twice a year and have appropriate lab work run when necessary.