Serum insulin concentrations in horses with equine Cushing's syndrome: response to a cortisol inhibitor and prognostic value.
Authors: McGowan C M, Frost R, Pfeiffer D U, Neiger R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Serum Insulin as a Prognostic Marker in Equine Cushing's Syndrome Elevated insulin concentrations commonly accompany equine Cushing's syndrome (ECS), yet their clinical significance and response to treatment remained unclear until this 2004 investigation. McGowan and colleagues monitored basal serum insulin in 20 confirmed ECS cases using six-hourly blood sampling over 24 hours, before and after initiating trilostane therapy (at 10 days, 30 days, and 1–2 years post-treatment). The research revealed a distinct diurnal rhythm with peak insulin at 1200 h that persisted regardless of trilostane administration; however, baseline insulin concentration emerged as a potent prognostic indicator, with horses showing <62 µIU/ml at the outset demonstrating significantly improved survival to 1–2 years (sensitivity and specificity >90%). Crucially, trilostane failed to normalise insulin concentrations long-term, despite mild elevation at the 10-day mark, suggesting insulin dysregulation in ECS operates independently of cortisol suppression. For practitioners, this work underscores that a single insulin measurement may be misleading given substantial 24-hour variation, but baseline values—optimally sampled at 1200 h—offer valuable prognostic information for counselling owners on long-term prognosis in newly diagnosed ECS cases.
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Practical Takeaways
- •Use serum insulin concentration as a prognostic indicator for ECS prognosis; baseline levels at 1200 h sampling provide the most reliable prediction of survival outcome
- •Be aware that single insulin samples may not be representative due to diurnal variation throughout 24 hours; consider timing of sampling or multiple measurements for accurate assessment
- •Expect that trilostane therapy will control cortisol but will not reverse elevated insulin concentrations, indicating that metabolic complications may persist despite successful treatment of ECS
Key Findings
- •Horses with ECS exhibit a diurnal pattern of serum insulin concentration with highest values at 1200 h, which is not altered by trilostane treatment
- •Low baseline serum insulin concentrations (< 62 microu/ml) at 1200 h were significantly associated with improved survival at 1-2 years with 90% sensitivity and specificity
- •High baseline serum insulin concentrations (> 188 microu/ml) predicted non-survival with 90% specificity
- •Serum insulin concentrations did not increase over 1-2 years in horses receiving trilostane therapy, despite mild increases at 10 days