Prevalence, risk factors and clinical signs predictive for equine pituitary pars intermedia dysfunction in aged...

Equine pituitary pars intermedia dysfunction (PPID) is an ageing-related neurodegenerative disorder. The prevalence and risk factors for PPID using seasonally adjusted basal adrenocorticotropic hormone (ACTH) concentrations in aged horses have not been previously reported.

To determine the prevalence, risk factors and clinical signs predictive for PPID in a population of horses aged ≥ 15 years in Queensland, Australia.

Owner-reported data was obtained using a postal questionnaire distributed to an equestrian group. A subgroup of surveyed owners were visited and a veterinary physical examination performed on all horses aged ≥ 15 years. Blood samples were analysed for basal plasma alpha melanocyte-stimulating hormone (α-MSH) and ACTH concentrations, routine haematology and selected biochemistry. Aged horses with elevations above seasonally adjusted cut-off values for basal plasma ACTH were considered positive for PPID. Positive horses were compared with their aged counterparts to determine risk factors and clinical signs associated with PPID.

Pituitary pars intermedia dysfunction was prevalent in aged horses (21.2%) despite owners infrequently reporting it as a known or diagnosed disease or disorder. Numerous clinical or historical signs were associated with an increased risk of PPID in the univariable model, but only age (odds ratio (OR) 1.18; 95% confidence interval (CI) 1.11-1.25, P<0.001) and owner-reported history of hirsutism (OR 7.80; 95% CI 3.67-16.57, P<0.001) remained in the final multivariable model. There were no routine haematological or biochemical variables supportive of a diagnosis of PPID.

Pituitary pars intermedia dysfunction occurs commonly in aged horses despite under-recognition by owners. The increased risk of PPID with age supports that this is an ageing associated condition. 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.