Glucocorticoid therapy and equine laminitis: fact or fiction?

Does oral prednisolone treatment increase the incidence of acute laminitis?

REASONS FOR PERFORMING STUDY

It is accepted among equine practitioners that glucocorticoid treatment is a risk factor for the development of laminitis. However, there is little published evidence of a link between glucocorticoids and laminitis.

OBJECTIVES

To determine whether horses receiving oral prednisolone are at increased risk of laminitis.

STUDY DESIGN

Retrospective case-control study.

METHODS

Clinical records of horses registered with the ambulatory service at Liphook Equine Hospital between January 2001 and November 2014 were reviewed retrospectively to identify horses that had received treatment with oral prednisolone. For each treated horse, 2 time-matched controls that received veterinary attention but were not treated with prednisolone were selected. Incidence of laminitis was compared between the 2 groups and factors associated with laminitis were assessed using Cox regression analysis.

RESULTS

Of the 416 horses treated with prednisolone, 16 (3.8%) were diagnosed with laminitis subsequent to the initiation of prednisolone treatment with an overall incidence of 2.60 (95% CI 1.49-4.22) cases per 100 horse-years at risk. A total of 7 horses (1.7%) developed laminitis during the course of their treatment and 3 (0.7%) of the horses treated with prednisolone were ultimately subjected to euthanasia as a result of laminitis. A total of 46 (5.7%), of the 814 time-matched control horses were diagnosed with laminitis during the study period with an overall incidence of 3.46 (95% CI 2.54-4.62) cases per 100 horse-years at risk. Of these, 12 (1.5%) were subjected to euthanasia as a result of laminitis. There were no significant differences in the overall laminitis incidence rate (P = 0.8), incidence rate during prednisolone treatment (P = 0.09), or probability of laminitis (P = 0.3) between the 2 groups. Mean survival time was greater in the prednisolone than the control group. Equine metabolic syndrome and increasing age were associated with increased risk of laminitis.

CONCLUSIONS

Administration of oral prednisolone did not increase the risk of laminitis.

Corticosteroid-associated laminitis

A direct causal association between corticosteroid use and laminitis has yet to be proven scientifically, and there have been few studies specifically addressing this aspect. New evidence, however, is improving the understanding of the causes of laminitis, particularly related to endocrine factors. The focus of this article is discussing the circumstances under which steroids might cause this condition.

Thermographic study of in vivo modulation of vascular responses to phenylephrine and endothelin-1 by dexamethasone in the horse

REASONS FOR PERFORMING STUDY

In vitro, glucocorticoids potentiate vasoconstriction of equine digital vessels to catecholamines and this has been implicated as a mechanism of glucocorticoid-induced laminitis. This observation has never been confirmed in vivo.

OBJECTIVES

To study the effects of glucocorticoid therapy on vasoconstrictor responsiveness in the horse in vivo.

METHODS

In a blinded, randomised cross-over experiment, 9 horses were treated with either dexamethasone (0.1 mg/kg bwt i.v. q. 24 h) or saline i.v. for 6 days. The changes in local average skin temperature before (baseline) and after intradermal injections of the alpha1-adrenoceptor agonist phenylephrine (PHE; 10(-4), 10(-5), 10(-6), 10(-7) and 10(-8) mol/l), endothelin-1 (ET-1; 10(-5), 10(-6), 10(-7), 10(-8) and 10(-9) mol/l) or ET-1 plus a blocker (BQ-123 10(-6) mol/l; RES-701 10(-6) mol/l; and L-NAME 10(-4) mol/l) were investigated with a thermograph.

RESULTS

Dexamethasone (DEX) decreased baseline skin temperatures, suggesting reduced blood flow as a consequence of an increase in vasomotor tone. This was accompanied by potentiation of the response to PHE as demonstrated by a left shift in the dose-response curve and a decrease in the EC50. Dexamethasone did not potentiate ET-1, but the interplay with the lower baseline temperature resulted in a significantly lower skin temperature for this vasoconstrictor after DEX. The different ET-1 blockers had no effect on ET-1 modulated skin temperatures.

CONCLUSIONS

Dexamethasone decreases skin perfusion. This is accompanied by a potentiated alpha1-adrenoceptor agonist response and a greater response to ET-1.

POTENTIAL RELEVANCE

Glucocorticoid therapy probably decreases perfusion of the equine hoof. During disease states that already are characterised by hypoperfusion and/or increased levels of circulating catecholamines, glucocorticoid therapy could, according to the vascular model of laminitis, tilt the balance in favour of laminitis.