• Epidemiology;
  • Equine;
  • Metabolic disease;
  • Pituitary par intermedia dysfunction


Pituitary pars intermedia dysfunction (PPID) is common in older horses.


To determine diagnosis frequency, prognostic factors, long-term survival, and owner satisfaction with treatment.


Medical records from horses diagnosed with PPID, 1993–2004.


A retrospective cohort design with data collected from the Veterinary Medical Data Base (VMDB) and a cohort of 3 VTHs. Proportional accessions, annual incidence, and demographics were compared for all accessions. During the same period, a subset of medical records (n = 44) was extracted and owners (n = 34) contacted to obtain long-term follow-up information.


Diagnoses of PPID were reported for 217 horses that presented to VTHs and were reported to the VMDB. Proportional diagnosis increased from 0.25/1,000 in 1993 to 3.72/1,000 in 2002. For 44 horses included in the follow-up study, the most commons signs were hirsutism (84%) and laminitis (50%). Of 34 horse owners contacted, the average time from onset of signs to diagnosis was 180 days. Improvement in ≥ 1 signs, 2 months after diagnosis, was reported by 9/22 (41%) of horse owners. Clinical signs and clinicopathologic data were not associated with survival, and 50% of horses were alive 4.6 years after diagnosis. Cause of death among horses (15/20; 85%) was euthanasia, and 11/15 (73%) were euthanized because of conditions associated with PPID. Most horse owners (28/29; 97%) said they would treat a second horse for PPID.

Conclusion and Clinical Importance

PPID was diagnosed with increasing frequency, and 50% of horses survived 4.5 years after diagnosis. Owners were satisfied with their horses' quality of life and would treat a second horse if diagnosed.