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

Objective The goal of this project was to examine the metabolic effects of IA methylprednisolone acetate (MPA) following injection into multiple low-motion joints. Methods Six 3-year-old geldings without pituitary pars intermedia dysfunction or insulin dysregulation were randomly injected with 20 mg of IA MPA/joint (80 mg total; bilateral distal hock joints) or an equal volume of saline. Serial blood samples were collected for resting ACTH, cortisol, insulin, and glucose, as well as insulin and glucose following repeated low-dose oral sugar tests. Treatments were crossed over after a 6-week washout, and the process was repeated. Results IA treatment with a total dose of 80 mg of MPA caused significant decreases in resting ACTH and cortisol concentrations between 4 and 12 hours after MPA injection. No significant effects of IA MPA treatment were noted in relation to resting insulin or glucose concentrations, nor were there any effects of IA MPA on insulin or glucose concentrations following low-dose oral sugar tests. Conclusions 80 mg of IA MPA in metabolically normal horses failed to induce significant changes in insulin and/or glucose, in contrast to data reported with other IA corticosteroids. Clinical Relevance With significant concern regarding corticosteroid-induced laminitis and the reported correlation of laminitis with IA corticosteroid administration, the present report provides additional information for equine veterinarians. Reported practitioner sentiment that IA MPA carries a lower risk for corticosteroid-induced laminitis may relate to the lack of postinjection hyperinsulinemia noted in this study. However, additional work in insulin-dysregulated and/or laminitis-prone horses is required before IA MPA should be considered safe to use in these horses.