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process, in which case the therapy should be directed at the primary agent and glucocorticoids might be contraindicated (Carlson 2009; Cottle and Hughes 2010). Response to glucocorticoid therapy is usually positive (Carlson 2009; Johns et al. 2011); however, in a report of a case of immune- mediated anaemia and thrombocytopenia, there was no response to doses as high as 0.2 mg/kg bwt i.v. once daily of dexamethasone, and the animal was subjected to euthanasia (McGovern et al. 2011; V€


a€ anen et al. 2013). an€


Neoplasia Lymphoma is one of the most common malignant neoplasms in the horse and originates from the lymphoid system (Taintor 2015). Neoplastic lymphocytes may arise from reactive B-cell clones producing antibodies responsible for gammopathies and immune-mediated processes. Lymphomas of B-cell, T-cell, and mixed B- and T-cell origin have been reported (Rendle et al. 2012). Equine lymphoma is classified as multicentric or generalised, alimentary, mediastinal, cutaneous, and solitary tumours of extranodal sites. Clinical signs may vary depending on the organs involved, however, horses more commonly present with weight loss, anorexia, or lethargy (Taintor 2015). Glucocorticoids for treatment of lymphoma have been


used alone or in conjunction of chemotherapeutic agents. In a case report of a horse diagnosed with a T-cell rich, B-cell lymphoma, cyclophosphamide and vincristine were used with dexamethasone at 0.04 mg/kg bwt orally on Day 1, and then decreased to 0.02 mg/kg bwt orally once daily from Day 2 to 30; this protocol was followed by the use of acyclovir, due to the horse testing positive for equine herpesvirus-5. The outcome was positive and one year after initiation of therapy the horse was reported to be in remission and had returned to its normal activities (Vander Werf and Davis 2013). Another protocol used prednisolone at 1.1–2.2 mg/kg bwt orally every 24 h, with the concomitant use of cyclophosphamide and cytosine arabinoside (Taintor and Schleis 2011). The duration of the glucocorticoid therapy is usually the same as the duration of the chemotherapy. Most of the chemotherapeutic protocols range from 2 to 3 months, then followed by a maintenance protocol consistent of gradual decreases of prednisolone (Aleman and Watson 2015b). Recurrence of the clinical signs are often observed once the therapy is discontinued (Taintor and Schleis 2011; Aleman and Watson 2015b). Therapy may be also attempted with glucocorticoids alone; using dexamethasone at 0.2 mg/kg bwt orally or i.v. once daily for 5 days, followed by prednisolone 1–2 mg/kg bwt orally once daily; however, the clinical response in affected horses after the use of this protocol was not described (Aleman and Watson 2015b). Treatment of a horse diagnosed with an angiotrophic T-cell lymphoma using one dose of dexamethasone at 0.1 mg/kg bwt i.v., followed by 10 days of prednisolone at 1 mg/kg bwt orally once daily, failed to respond to therapy and had a fatal outcome (Raidal et al. 2006).


Although some periods of remission have been reported,


the long-term prognosis for this condition has been poor, and glucocorticoid treatment in cases of lymphoma rarely ameliorate the clinical condition, even with the concomitant use of chemotherapeutic drugs (Raidal et al. 2006). Due to the low number of reported cases treated with chemotherapy, there is limited information available, and dosages are extrapolated from other species. Pharmacokinetic studies in


horses are needed to incorporate proper usage of these drugs. It is also difficult to assess the effect of the glucocorticoids in cases of remission, since chemotherapy was used concomitantly; therefore, studies using glucocorticoids alone are necessary to make conclusions.


Conclusion


Glucocorticoids are known to be drugs with a potent and rapid effect to decrease inflammation and are successfully used to treat many systemic inflammatory conditions in horses. Adverse effects such as delayed wound healing, immunosuppression, laminitis, gastric ulceration or adrenal suppression have been linked to the treatment with glucocorticoids, especially with higher doses or long duration of therapy (Flaminio et al. 2009; Bailey 2010; Ivester and Cou€


etil 2014). There is little scientific evidence to support


some of the attributed adverse effects of glucocorticoids in horses, such as the development of laminitis, which is based on anecdotal case reports (Bailey 2010). A study showed no correlation between treatment with glucocorticoids and the occurrence of gastric ulcers in racehorses (Murray et al. 1996); however, glucocorticoid therapy increases the risk of gastric ulceration in human patients and small animals (Boothe and Mealey 2012; Filaretova et al. 2014). More studies to identify the risk for the development of gastric ulcers in horses after high doses or prolonged therapies with glucocorticoids are warranted. Depending on the condition to be treated and the severity, there is a wide variation of dosages among the literature reviewed, and the decision whether or not to use steroidal anti-inflammatory medications


should be supported by historical and physical examination findings, and laboratory data and followed by close monitoring (Ivester and Cou€


etil 2014).


Authors’ declaration of interests No conflicts of interest have been declared.


Ethical animal research Ethical review not applicable for this review article.


Source of funding No source of funding.


Authorship


All authors were involved in manuscript preparation and review. The final manuscript was approved by all the authors.


References Ainsworth, D.M. and Cheetham, J. (2010a) Disorders of the respiratory system. In: Equine Internal Medicine, 3rd edn., Eds: S.M. Reed, W.M. Bayly and D.C. Sellon, Saunders Elsevier, St Louis. pp 344-346.


Ainsworth, D.M. and Cheetham, J. (2010b) Disorders of the respiratory system. In: Equine Internal Medicine, 3rd edn., Eds: S.M. Reed, W.M. Bayly and D.C. Sellon, Saunders Elsevier, St Louis. pp 327.


Aleman, M. and Watson, J.L. (2015a) Acquired hemostatic disorders. In: Large Animal Internal Medicine, 5th edn., Ed: B.P. Smith, Elsevier, St Louis. pp 1048-1049.


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