Plasma adrenocorticotropin (ACTH) concentrations and clinical response in horses treated for equine Cushing's disease with cyproheptadine or pergolide.
Authors: Perkins G A, Lamb S, Erb H N, Schanbacher B, Nydam D V, Divers T J
Journal: Equine veterinary journal
Summary
# Editorial Summary: ACTH Monitoring in Equine Cushing's Disease Treatment Determining optimal treatment response in equine Cushing's disease (ECD) remains challenging because clinical improvement doesn't always correlate with plasma ACTH concentrations, prompting Perkins and colleagues to evaluate whether ACTH monitoring could reliably guide therapy with cyproheptadine or pergolide. The researchers validated a chemiluminescent ACTH assay for accuracy and stability, assessed the diagnostic sensitivity (84%) and specificity (78%) of elevated ACTH for detecting ECD in hospitalised horses, and surveyed veterinarians treating ECD cases to determine whether serial ACTH measurements predicted clinical response. Both drugs produced variable reductions in plasma ACTH levels, yet treated horses generally demonstrated clinical improvement regardless of ACTH suppression patterns—a finding that challenges the assumption that ACTH normalisation is necessary for therapeutic success. For practitioners, this work suggests that whilst ACTH measurement can form part of the monitoring toolkit, clinical assessment of signs such as coat quality, weight loss and hyperhydrosis should remain the primary indicators of treatment efficacy; notably, neither cyproheptadine nor pergolide showed superiority in clinical outcomes, supporting a pragmatic approach to drug selection based on individual horse factors and client circumstances rather than predicted ACTH response.
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Practical Takeaways
- •Clinical improvement in signs (coat quality, muscle tone, laminitis) should be the primary endpoint for ECD treatment success, not plasma ACTH normalization alone
- •Plasma ACTH monitoring may be useful as a supplementary tool during therapy but should not replace clinical assessment
- •Both cyproheptadine and pergolide appear similarly effective; treatment choice may be based on availability, cost, and individual horse response rather than expected biochemical outcomes
Key Findings
- •ACTH chemiluminescent assay was validated with acceptable specificity, precision, and accuracy for detecting ECD
- •Plasma ACTH had 84% sensitivity and 78% specificity for detecting ECD in hospitalized horses (n=68)
- •Treated horses generally showed decreased plasma ACTH levels, but clinical improvement was inconsistent with ACTH reduction
- •No significant differences between cyproheptadine (n=32) and pergolide (n=10) in clinical sign improvements