Erythema Multiforme and its Clinicopathological Features in a Horse in Brazil

Pollyana Rennó Campos Braga, Lissandro Gonçalves Conceição, Fabricia Hallack Loures, Roberta Martins Basso, José Paes de Oliveira Filho, Alexandre Secorun Borges


Background: Erythema multiforme (EM) is an immune-mediated skin disease which may manifest as cutaneous or mucocutaneous lesions. It is uncommon in horses. EM lesions have a symmetrical bilateral distribution; they are usually urticarial, necrotizing, and, less commonly, ulcerative. In equines, the trigger is usually unknown, and cases are often classified as idiopathic. Diagnosis is based on a thorough history and physical and histopathological examination of lesions. According to the clinical presentation and histopathological characteristics of the cutaneous lesions, this case is the first report to describe diagnosis and treatment of a horse with EM in Brazil.

Case: A Quarter Horse filly was followed clinically for 12 months after sudden onset of skin lesions at 18 months of age. The initial lesions were non-alopecic papules with a symmetrical bilateral distribution. Six months after onset, the skin lesions maintained the original distribution pattern; however, they had progressed to papules and plaques with varying annular, arciform, serpiginous, targetoid, or alopecic appearance. At 8 months, the same distribution pattern and appearance remained, but the lesions had become more severe and extensive, with involvement of the labial commissures and perineal region, without any erosions/ulcerations, scaling/crusting, pain, or pruritus. At 12 months, new nodular lesions were found on the medial and lateral surfaces of the hind limbs, neck, bilateral trunk, and root of the tail. The lesions were firm, non-pruritic, and non-tender on palpation. Swabs were obtained from the papular lesions. Skin specimens were also obtained with a 6-mm punch and via incisional biopsy and histological sections were made. Bacterial and fungal cultures were negative. Appropriate stains did not identify fungal structures, were negative for acid-fast bacilli, and did not reveal any metachromatic granules in the sampled cell population. The histopathological findings were characteristic of immune-mediated disease, with a vacuolar interface dermatitis affecting the hair follicles more than the epidermis, necrotic keratinocytes, lymphocyte satellitosis, leukocytoclastic mixed vasculitis of the mid-dermis and deep dermis, and variable granulation tissue, consistent with erythema multiforme and leukocytoclastic vasculitis. Immunosuppressive therapy with corticosteroids and oral supplementation with omega-3 and omega-6 fatty acids and vitamin E were prescribed. After institution of therapy, no new lesions developed, the existing lesions remained stable (though permanent), and hair regrew in the previously alopecic areas. All physiological parameters remained normal throughout the follow-up period.

DiscussionErythema multiforme is rarely reported in horses. According to our literature review, this is the first description of EM in horses in Brazil. EM should be included in the differential diagnosis of horses that present with plaques in a diverse, geographic distribution and a negative initial dermatological screening examination. Further clinical investigation is warranted, with special attention to potential antigenic triggers. A thorough drug and dietary history and close attention to comorbidities are essential, as the suppression of potential culprit factors has important prognostic value and contributes to the elucidation of EM triggers.

Full Text:



Ackerman L.J. 1989. Miscellaneous Skin Disordens. In: Pratt P.W. (Ed). Practical Equine Dermatology. Goleta: American Veterinary Publications, pp.157-178.

Affolter V.K. & Von Tscharner C. 1992. Cutaneous Drug Reactions: a Retrospective Study of Histopathological Changes and their Correlation with the Clinical Disease. Veterinary Dermatology. 3(4-5): 157-163.

Auquier-Dunant A., Mockenhaupt M., Naldi L., Correia O., Schröder W. & Roujeau J. 2002. Correlations between clinical pattern and causes of erythema multiforme majus, Steven-Johnson syndrome and toxic epidermal necrolysis. Archives Dermatology. 138(8): 1019-1024.

Bedi T.T. & Pinkus H. 1976. Histopathological spectrum of erythema multiforme. British Journal of Dermatology. 95(3): 243-250.

Burbulys D. & Young K.D. 2018. Erythema Multiforme. In: Rose E. (Ed). Life-Threatening Rashes. New York: Springer International Publishing AG, part of Springer Nature, pp.55-77.

Criado P.R., Criado R.F.J., Vasconcellos C., Ramos R.O. & Gonçalves A.C. 2004. Reações cutâneas graves adversas a drogas - aspectos relevantes ao diagnóstico e ao tratamento - Parte I - anafilaxia e reações anafilactóides, eritrodermias e o espectro clínico da síndrome de Stevens-Johnson & necrólise epidérmica tóxica (Doença de Lyell). Anais Brasileiros de Dermatologia. 79(4): 471-488.

Fadok V.A. 1995. Overview of Equine Papular and Nodular Dermatoses. Veterinary Clinics of North America: Equine Practice. 11(1): 61-74.

Fadok V.A. 1995. Update on Four Unusual Equine Dermatoses. Veterinary Clinics of North America: Equine Practice. 11 (1):105-110.

Gross T.L., Ihrke P.J. & Walder E.J. 1992. In: Reinhardt R.W. (Ed). Veterinary Dermatopathology. St. Louis: Mosby Year Book, pp.41-46.

Herder V., Barsnick R., Walliser U., Teifke J.P., König P., Czerwinski G., Hansmann F., Baungärtner W. & Hewicker-Trautwein M. 2012. Equid herpesvirus 5-associated dermatitis in a horse - Resembling herpes-associated erythema multiforme. Veterinary Microbiology. 155(2-4): 420-424.

Huff J.C., Weston W.L. & Tonnesen M.G. 1983. Erythema multiforme: A critical review of characteristics, diagnostic criteria, and causes. Journal of the American Academy of Dermatology. 8(6): 763-775.

Itoh T., Nibe K., Kojimoto A., Mikawa M., Mikawa K., Uchida K. & Shii H. 2006. Erythema multiforme possibly triggered by food substances in a dog. Journal Veterinary Medicine Science. 68(8): 869-871.

James A., Krippaehne J.A. & Montgomery M.T. 1992. Erythema multiforme: a literature review and case report. Special Care in Dentistry. 12(3): 125-130.

Knottenbelt D.C & Mcgarry J.W. 2009. Immune-mediated/allergic diseases. In: Edwards R. (Ed). Pascoe’s Principles & Practice of Equine Dermatology. 2nd edn. London: Saunders Elsevier, pp.253-297.

MacLeod K.D., Scott D.W. & Erb H.N. 2004. The Prevalence of Apoptotic Keratinocytes in Equine Epidermis: A Retrospective Light-microscopic Study of Skin-biopsy Specimens from 253 Horses with Normal Skin or Inflammatory Dermatoses. Journal of Veterinary Medicine. 51(9-10): 400-404.

Marshall C. 1991. Erythema multiforme in two horses. Journal of the South African Veterinary Association. 62(3): 133-136.

Martinez R.S., Andrade D.M.R., Scabar L.F. & Giovani E.M. 2010. Abordagem dos aspectos atuais do eritema multiforme e a Odontologia. Journal of the Health Sciences Institute. 28(3): 251-254.

Oliveira F.L., Silveira L.K., Morais T.S. & Serra M.C.V. 2012. Necrólise epidérmica tóxica e síndrome de Stevens Johnson: atualização. Revista Brasileira de Queimaduras. 11(1): 26-30.

Oryan A., Ghane M. & Ahmadi N. 2010. Erythema multiforme and its clinicopathological disorders in a horse. Comparative Clinical Pathology. 19(2): 179-184.

Pascoe R.R.R & Knottenbelt D.C. 1999. Immune-Mediated/Allergic Diseases. In: Byers C. (Ed). Manual of Equine Dermatology. London: W.B. Saunders, pp.155-181.

Peters-Kennedy J. & Ruby R.E. 2015. Bullous Diseases of the Skin and Mucosa. In: Felippe M.J.B. (Ed). Equine Clinical Immunology. Hoboken: Wiley Blackwell, pp.61-64.

Potocnik E., Drozdzewska K. & Schwarz B. 2019. Presumed Sulfonamide-Associated Uveitis with Stevens-Johnson Syndrome in a Quarter Horse Mare. Journal of Equine Veterinary Science. 77:17-22.

Rakhi I. & Prabhu N. 2017. Etiopathogenesis of Erythema Multiforme - A Concise Review. Advances in Dentistry & Oral Health. 5(4): 1-5.

Rosenkrantz W. 2013. Immune-Mediated Dermatoses. Veterinary Clinics of North America: Equine Practice. 29(3): 607-613.

Samim F., Zed C. & Williams P.M. 2013. Erythema Multiforme a Review of Epidemiology, Pathogenesis, Clinical Features, and Treatment. Dental Clinics of North America. 57(4): 583-596.

Scott D.W. 1991. Unusual Immune-mediated Skin Diseases in the horse. Equine Practice. 13(2): 10-18.

Scott D.W. & Miller W.H. 1997. Idiossyncratic cutaneous adverse drugs reactions in the horse: Literature review and report of 19 cases (1990-1996). Equine Practice. 19(10): 12-15.

Scott D.W. & Miller W.H. 1998. Erythema multiforme in the horse: Literature review and report of 9 cases (1988-1996). Equine Practice. 20(6): 6-9.

Scott D.W. & Miller W.H. 1999. Erythema multiforme in dogs and cats: literature review and case material from the Cornell University College of Veterinary Medicine (1988-96). Veterinary Dermatology. 10(4): 297-309.

Scott D.W. & Miller W.H. 2010. Immune-Mediated Disorders. In: Equine Dermatology. 2nd edn. Maryland Heightscap: Elsevier Saunders, pp.314-359

Scott D. W., Walton D.K. & Blue M. G. 1984. Erythema multiforme in a horse. Equine Practice. 6(8): 26-30.

Scott D.W., Walton D.K., Slater M.R., Smith C.A & Lewis R.M. 1987. Immune-mediated Dermatoses in Domestic Animals: Ten years after- Part II. Compendium on Continuing Education. 9(5): 539-553.

Sloet van Oldruitenborgh-Oosterbaan M.M. & Goehrin L.S. 2011. Immune-mediated skin diseases in the horse. Pferdeheilkunde Equine Medicine. 17(4): 346-356.

Stannard A.A. 2000. Immunology Diseases. Veterinary Dermatology. 11: 163-178.

Van Poucke S., Van Houwermeiren H., Hunt L., Chiers K. & Ducatelle R. 2005. Erythema multiforme in a Pony. Vlaams Diergeneeskin Tijdschrift. 74(5): 355-359.


Copyright (c) 2021 Pollyana Rennó Campos Braga, Lissandro Gonçalves Conceição, Fabricia Hallack Loures, Roberta Martins Basso, José Paes de Oliveira Filho, Alexandre Secorun Borges

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.