Intra-articular methylprednisolone acetate does not induce hyperinsulinemia or hyperglycemia in metabolically normal horses.

Overview

• This study investigated whether injecting methylprednisolone acetate (MPA), a corticosteroid, into the joints of metabolically normal horses causes increases in insulin or glucose levels (hyperinsulinemia or hyperglycemia).
• The results indicated that intra-articular MPA did not induce these metabolic changes, suggesting it may be safer regarding glucose metabolism compared to other corticosteroids, though further studies are needed in metabolically compromised horses.

Background and Purpose

• Corticosteroids are often used to treat joint inflammation in horses but may cause metabolic side effects like increased insulin or glucose levels, which can contribute to laminitis, a painful hoof condition.
• Methylprednisolone acetate (MPA) is one corticosteroid used intra-articularly (inside the joint), but its effects on metabolic parameters such as insulin and glucose levels have not been fully explored in normal horses.
• The goal was to assess if injecting MPA into low-motion joints elevates resting or postprandial insulin and glucose levels, indicating metabolic disruption.

Study Design and Methods

• Subjects: Six 3-year-old gelding horses without known metabolic disorders (no pituitary pars intermedia dysfunction or insulin dysregulation).
• Intervention: Each horse received intra-articular injections of methylprednisolone acetate (20 mg per joint) into bilateral distal hock joints (total dose 80 mg) in one period, and an equal volume of saline in the other, with treatments crossed over after a 6-week washout.
• Measurements:
  • Resting blood levels of ACTH (adrenocorticotropic hormone), cortisol, insulin, and glucose at various time points post-injection.
  • Low-dose oral sugar tests performed repeatedly to assess insulin and glucose response after treatment.

Key Findings

• Significant decreases in resting ACTH and cortisol levels occurred between 4 and 12 hours after MPA injection, consistent with corticosteroid feedback on the hypothalamic-pituitary-adrenal axis.
• No significant changes were observed in resting insulin or glucose concentrations following MPA treatment compared to saline.
• There were no significant differences in insulin or glucose levels during oral sugar tests after MPA injection, indicating no effect on insulin sensitivity or glucose metabolism in these horses.
• These results contrast with earlier studies showing hyperinsulinemia or hyperglycemia after intra-articular use of other corticosteroids.

Clinical Significance

• The absence of hyperinsulinemia or hyperglycemia suggests intra-articular MPA may carry a lower risk of inducing laminitis related to metabolic disturbance in metabolically normal horses.
• This finding supports the perception among veterinarians that MPA is potentially safer for joint injections compared to other corticosteroids.
• However, the study was limited to horses without metabolic dysfunction, so the safety of MPA in insulin-dysregulated or laminitis-prone horses remains unclear.
• Additionally, the study highlights the importance of cautious corticosteroid use, and recommends further research involving at-risk populations before broadly considering MPA safe in those groups.

Summary

• Intra-articular methylprednisolone acetate injections in healthy horses do not cause harmful increases in insulin or glucose, unlike some other corticosteroids.
• The study provides valuable data on metabolic safety for equine practitioners when selecting corticosteroid treatments for joint inflammation.
• Further investigations are needed to confirm safety in horses with existing metabolic disorders or laminitis risk.