South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
abnormal biochemical findings may include elevations in liver enzyme activities,
hypercholesterolemia, and hypertriglyceridemia.
Diagnosis: Practically, the diagnosis of PPID is most commonly made by observation of
hypertrichosis and other clinical signs in older equids. However, establishing a diagnosis of PPID
in less severely affected animals can be challenging. As a result, a number of endocrinologic tests
have been used to evaluate horses with suspected PPID. Recently, the PPID Diagnosis Working
Group of the Equine Endocrine Society developed a consensus statement
(http://sites.tufts.edu/equineendogroup/files/2013/11/EEG-recommendations-downloadablefinal.pdf) for the approach to diagnosis of PPID. Testing involves Tier 1 tests (screening tests) and
Tier 2 tests for further evaluation of horses with inconclusive Tier 1 test results. Tier 1 tests
include measurement of plasma ACTH concentration and the overnight dexamethasone
suppression test and the currently recommended Tier 2 test is assessment of the ACTH response
to thyrotropin releasing hormone (TRH). It warrants emphasis that the vast majority of
experimental work evaluating diagnostic tests for PPID has been performed on horses; thus,
extrapolation of findings to ponies and other equids has not been well validated.
Plasma ACTH concentration (Tier 1). Equids with PPID have excessive amounts of ACTH and
ACTH-like peptides in abnormal PI tissue and increased amounts are released into plasma. Th \