Can Endocrine Dysfunction Be Reliably Tested in Aged Horses That Are Experiencing Pain?

Abstract

The aim of the present study was to evaluate (i) the effects of different intensities and types of treated pain on the basal concentrations of adrenocorticotropic hormone (ACTH) and cortisol, and (ii) the thyrotropin-releasing hormone (TRH) stimulation test, to determine whether treated pain caused a marked increase of ACTH, which would lead to a false positive result in the diagnosis of pituitary pars intermedia dysfunction (PPID). Methods: Fifteen horses with treated low to moderate pain intensities were part of the study. They served as their own controls as soon as they were pain-free again. The horses were divided into three disease groups, depending on their underlying disease (disease group 1 = colic, disease group 2 = laminitis, disease group 3 = orthopedic problems). A composite pain scale was used to evaluate the intensity of the pain. This pain scale contained a general part and specific criteria for every disease. Subsequently, ACTH and cortisol were measured before and after the intravenous application of 1 mg of TRH. Results: There was no significant difference in the basal or stimulated ACTH concentration in horses with pain and controls, between different pain intensities or between disease groups. Descriptive statistics, however, revealed that pain might decrease the effect of TRH on the secretion of ACTH. There was an increase of ACTH 30 min after TRH application (p = 0.007) in the treated pain group, but this difference could not be statistically confirmed. Measuring the basal ACTH concentration and performing the TRH stimulation test for the diagnosis of PPID seem to be possible in horses with low to moderate pain.

BEVA primary care clinical guidelines: Diagnosis and management of equine pituitary pars intermedia dysfunction

“…In total, 25 publications 41,44–67 and seven abstracts 43,68–73 were identified that provided data on the interpretation of diagnostic test results (Table S4). A summary of the key recommendations is presented in Table 9.…”

“…Two publications 54,60 were identified. One 51 indicated that there was no effect of moderate pain on basal ACTH concentrations or the ACTH response to TRH.…”

Influence of feeding and other factors on adrenocorticotropin concentration and thyrotropin‐releasing hormone stimulation test in horses and ponies

“…10 Furthermore, the blood collection after 30 min is reported to be less affected by the timing of the sample collection. 8,28,53 Finally, the acute stress seen in a few horses might have also influenced our results, 16,54 especially in horses that were isolated from the herd for fasting.…”

“…1,14 Ageing, severe disease, acute pain and stress also increase the bACTH. [15][16][17][18] The significant effect of breed, colour and sex on the bACTH was also shown, with ponies, grey horses and mares having a higher bACTH in the autumn. 17,19 Studies investigating the influence of the body condition score (BCS) on the bACTH are lacking, however, it warrants further investigation as obesity and appetite correlates with dopaminergic tone in humans.…”

Markers for internal neoplasia in the horse

“…Although animals with severe pain have higher plasma ACTH concentrations (Stewart et al., 2019 ), they remain stable in patients with chronic, mild‐to‐moderate pain (Gehlen et al., 2020 ), which enables diagnostic in horses presented with diseases such as laminitis (Gehlen et al., 2020 ). However, testing in a visibly excited or stressed animal (e.g., after transport or during bad weather) is not recommended, as it causes a temporary release of ACTH into the circulation (Chapman et al., 2017 ; Haffner et al., 2020 ).…”