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22-05-2012 | Veterinary medicine | Article

‘Equine Cushing’s syndrome’ more common than thought

Abstract

Free abstract

MedWire News: Pituitary pars intermedia dysfunction (PPID) is a common but under-recognized disorder in aged horses, UK veterinarians believe.

Noting that PPID typically affects animals over 15 years of age, they recommend that aged horses with characteristic signs, such as hirsutism, should be tested and treated as appropriate.

PPID, or equine Cushing's syndrome, is a neurodegenerative disorder associated with aging. It results from a loss of dopaminergic inhibition of the PPI and manifests as excessive hair coat length, coat shedding, weight loss, increased muscle catabolism, and/or signs of depression.

"Unequivocal hirsutism has been considered pathognomonic for PPID and the demonstration of either hirsutism or hirsutism and one or more other clinical signs of PPID has been used as a means for diagnosis of PPID," note Catherine McGowan (University of Liverpool, Neston) and co-authors writing in Equine Veterinary Journal.

While hirsutism is highly specific for PPID, it is not particularly sensitive, so McGowan's group used a biochemical marker to characterize PPID more accurately in a population of aged horses.

The marker they chose was plasma basal adrenocorticotropic hormone (ACTH), which was assessed in 324 horses aged 15 years and over. Using seasonally adjusted ACTH cutoff values, 21.2% of horses had PPID.

By contrast, just 14.2% had PPID reported by their owners, McGowan et al report, indicating that the condition is under-recognized.

Interestingly, horses with a biochemic diagnosis of PPID were significantly older than those with a negative ACTH test, at 24.0 versus 18.8 years.

In univariate analysis, a raft of factors was found to be associated with a biochemical diagnosis of PPID, including age, hirsutism, depression, increased appetite, wasted topline, pot belly, divergent rings, laminitis, fibrinogen levels, and gamma glutamyltransferase.

In the final multivariate model, however, just two factors ‑ age (as a continuous variable) and owner-reported history of hirsutism ‑ were significantly and independently associated with PPID, at odds ratios of 1.18 and 7.80, respectively.

The researchers conclude: "The current study has shown the prevalence of PPID in horses aged 15 years and older to be 21% based on the criteria of basal plasma ACTH concentrations being elevated above seasonally adjusted reference ranges.

"Aged horses with clinical or historical signs consistent with PPID, especially owner reported hirsutism (delayed shedding and/or long hair coat), should be tested and appropriate treatment instituted."

By Joanna Lyford