Factors associated with survival, laminitis and insulin dysregulation in horses diagnosed with equine pituitary pars intermedia dysfunction

Abstract

Summary Background Pituitary pars intermedia dysfunction (PPID) is a commonly described endocrine disorder in higher latitudes of the Northern hemisphere but the description of the disease at lower latitudes and in the Southern hemisphere is limited. Objectives Document the clinical features of PPID at different Australian latitudes and climates, and investigate factors associated with survival, laminitis and insulin dysregulation (ID). Study design Retrospective study of 274 equids from eight institutions across Australia. Methods A diagnosis of PPID was based on endogenous ACTH, overnight dexamethasone suppression test, thyrotropin‐releasing hormone stimulation test or necropsy. Clinical and clinicopathologic characteristics of PPID and therapeutic responses were investigated. Laminitis was diagnosed by radiographic or histologic changes and ID was diagnosed based on endogenous insulin, an oral glucose test or a 2‐step insulin‐response test. Results Being a pony, having a higher body condition score and pergolide administration were associated with survival. The clinical presentation of PPID changed with latitude and climate, with anhidrosis and polyuria/polydipsia more commonly recognised at lower latitudes. Laminitis was diagnosed in 89.9% of cases and ID was present in 76.5% of cases in which they were investigated. Main limitations Despite the sample size, the lack of uniform testing at all locations (primary or referral cases) and the incompleteness of data sets limited the power of the statistical analyses. Conclusions PPID can present with variable signs at different latitudes and climates, and ID should be investigated in equids diagnosed with PPID. Adequate body condition and administration of pergolide are fundamental in PPID management.

Effect of thyrotropin‐releasing hormone stimulation testing on the oral sugar test in horses when performed as a combined protocol

“…Regardless of the reason, the low number of horses with increased ACTH, especially after the TRH stimulation test, precludes any conclusion from being drawn concerning the effect of high ACTH after TRH on OST outcome. Horses with PPID and ID have higher endogenous ACTH concentrations than do horses with PPID and no evidence of ID . A similar relationship was appreciated with increasing insulin concentrations observed as resting ACTH concentrations increased in the current study, although small numbers preclude accurate conclusions from being drawn on the effect of ACTH concentration on OST results.…”

The effect of freeze‐thaw cycles on determination of immunoreactive plasma adrenocorticotrophic hormone concentrations in horses

“…Based on previous studies, the prevalence of PPID in horses and ponies >15 years of age is as high as 21% 1,2 . Clinical signs shown in advanced stages of PPID, such as hypertrichosis, pendulous abdomen, or laminitis, can be easily recognized but can be absent in some equids, especially in the early stages of the disease, thus limiting the sensitivity of a clinical diagnosis 3‐5 . Currently, necropsy is considered the most accurate method to diagnose PPID.…”

Evaluation of combined testing to simultaneously diagnose pituitary pars intermedia dysfunction and insulin dysregulation in horses

“…Several tests have been developed to diagnose ID, some assessing insulin response to a glucose challenge, some assessing glucose response to an insulin challenge, and some assessing both . The oral glucose test and oral sugar test (OST) are commonly used tests and are based on the PO administration of dextrose or corn syrup to fasted horses and measurement of the insulin response to determine the presence of hyperinsulinaemia . These tests require an 8‐hour to 10‐hour fast as well as 2 hours to complete the test .…”