Polioencephalomalacia in Sheep - Clinical and Magnetic Resonance Imaging Findings


  • Fabrício Moreira Cerri Universidade Estadual Paulista (Unesp), Faculdade de Medicina Veterinária e Zootecnia, Botucatu, SP, Brazil https://orcid.org/0000-0001-6074-0105
  • Isabella Mendonça Zanella Cecconi Cardoso Universidade Estadual Paulista (Unesp), Faculdade de Medicina Veterinária e Zootecnia, Botucatu, SP, Brazil. https://orcid.org/0000-0003-3275-0618
  • Vânia Maria de Vasconcelos Machado Universidade Estadual Paulista (Unesp), Faculdade de Medicina Veterinária e Zootecnia, Botucatu, SP, Brazil. https://orcid.org/0000-0002-9057-5793
  • José Paes de Oliveira-Filho Universidade Estadual Paulista (Unesp), Faculdade de Medicina Veterinária e Zootecnia, Botucatu, SP, Brazil. https://orcid.org/0000-0001-9890-2640
  • Rogério Martins Amorim Universidade Estadual Paulista (Unesp), Faculdade de Medicina Veterinária e Zootecnia, Botucatu, SP, Brazil. https://orcid.org/0000-0003-3750-5857
  • Alexandre Secorun Borges Universidade Estadual Paulista (Unesp), Faculdade de Medicina Veterinária e Zootecnia, Botucatu, SP, Brazil. https://orcid.org/0000-0001-6256-8089
  • Danilo Giorgi Abranches de Andrade Universidade Estadual Paulista (Unesp), Faculdade de Medicina Veterinária e Zootecnia, Botucatu, SP, Brazil https://orcid.org/0000-0003-0305-4154




Background: Polioencephalomalacia (PEM) is a neurological disease in ruminants, which is characterized by malacia of brain gray matter. Thiamine deficiency and sulfur intoxication are the most common causes of PEM in sheep. Affected animals present signs of cerebrocortical syndrome, including amaurosis, ataxia, head pressing, mental depression, seizures, and opisthotonus. The neurological examination aims to determine the neurolocalization of the lesions and advanced imaging techniques are useful for confirming the affected area(s) in the central nervous system. The aim of this study is to describe clinical features and ante-mortem diagnosis using magnetic resonance imaging (MRI) in a sheep with PEM.

Case: An 18-month-old male Dorper sheep from a flock started receiving concentrate 7 days before. According to the owner, no clinical signs of abnormality were observed on the previous morning. However, in the afternoon, the animal became self-isolated and did not follow the flock to the sheepfold. The following day, he was found in recumbency. Physical examination revealed lateral recumbency, rectal temperature 39.5ºC, 52 bpm, 120 bpm, congested mucous membranes, capillary refill time 1 s, ruminal (4/5 min) and intestinal hypomotility. The assessment of the central nervous system revealed a decreased level of consciousness, focal seizures, opisthotonus, and absence of menace response. The following differential diagnoses were listed: PEM, head trauma, focal symmetrical encephalomalacia, bacterial encephalitis, and rabies. Treatment was composed of dexamethasone [0.2 mg/kg - i.v., SID (1st-3rd day), 0.1 mg/kg, i.v., SID (4th-6th day), and 0.05 mg/kg, i.v., SID (7th-9th day)]; mannitol [1 g/kg -  i.v. and diazepam 0.4 mg/kg, i.v. single dose at admission]; vitamin B1 [10 mg/kg - i.m., SID], furosemide [1 mg/kg - i.v., SID for 3 days] and sulfadoxine/trimethoprim [30 mg/kg -  i.m., SID for 10 days]. After the initial treatment, the patient showed mild clinical improvement; however, the amaurosis was still present. Magnetic resonance imaging of the brain was performed on the 2nd day of hospitalization, showing a symmetrical hypersignal in the parietal and occipital cortices, in the axial and sagittal sequences weighted in T2 and FLAIR.

Discussion: This study aimed to describe the clinical signs and MRI findings in a sheep with PEM. In this case, the sudden change to the feed composition probably led to ruminal dysbiosis, inhibition of thiamine-producing microorganisms and proliferation of bacteria that synthesize thiaminase. Thiamine therapy proved to be effective and capable of reverting the clinical signs. The decrease in the level of consciousness, cortical blindness, and opisthotonus are due to alterations in the parietal cortex, in the occipital cortex, and in the cerebellum, respectively, which were demonstrated by hypersignal areas in the MRI. Therefore, the neurolocalization of the lesion based on neurologic examination and the MRI findings were related. The physicochemical and cytological evaluations of the cerebrospinal fluid, and dosage of thiamine and the concentration of hydrogen sulphide in the rumen were not performed. However, the response to thiamine treatment associated with the neurologic examination and MRI findings helped in determining the diagnosis. Additionally, MRI can be used as a useful tool for the ante mortem diagnosis of PEM.

Keywords: cerebrocortical necrosis, diagnostic imaging, neurology, ruminants, thiamine deficiency.


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Borges A.S., Lisbôa J.A.N., Braga P.R.C., Leite R.O. & Queiroz G.R. 2021. Doenças neurológicas dos ruminantes no Brasil: exame e diagnóstico diferencial. Revista Brasileira de Buiatria. 1: 63-99.

Bourke C.A., Rendell D. & Colegate S.M. 2003. Clinical observations and differentiation of the peracute Phalaris aquatica poisoning syndrome in sheep known as ‘Polioencephalomalacia-like sudden death’. Australian Veterinary Journal. 81: 698-700.

Cebra C.K. & Cebra M.L. 2004. Altered mentation caused by polioencephalomalacia, hypernatremia, and lead poisoning. Veterinary Clinics of North America: Food Animal Pratice. 20: 287-302.

Cunha P.H.J., Bandarra P.M., Dias M.M., Borges A.S. & Driemeier D. 2010. Outbreak of polioencephalomalacia in cattle consuming high sulphur diet in Rio Grande do Sul, Brazil. Pesquisa Veterinária Brasileira. 30: 613-617.

Ertelt K., Oevermann A., Precht C., Lauper J., Henke D. & Gorgas D. 2016. Magnetic resonance imaging findings in small ruminants with brain disease. Veterinary Radiology & Ultrasound. 57: 162-169.

Gould D.H. 1998. Polioencephalomalacia. Journal of Animal Science. 76: 309-314.

Lee K., Yamada K., Tsuneda R., Kishimoto M., Shimizu J., Kobayashi Y., Furuoka H., Matsui T., Sasaki N., Ishii M., Inokuma H., Iwasaki T. & Miyake Y. 2009. Clinical experience of using multidetector-row CT for the diagnosis of disorders in cattle. The Veterinary Record. 165: 559-562.

Lima E.F., Riet-Correa F., Tabosa I.M., Dantas A.F.M., Medeiros J.M. & Sucupira Júnior G. 2005. Polioencephalomalacia in goats and sheep in the semiarid region of northeastern Brazil. Pesquisa Veterinária Brasileira. 25: 9-14.

Pimentel L.A., Oliveira D.M., Galiza G.J.N., Dantas A.F.M., Uzal F. & Riet-Correa F. 2010. Focal symmetrical encephalomalacia in sheep. Pesquisa Veterinária Brasileira. 30: 423-427.

Precht C., Vermathen P., Henke D., Staudacher A., Lauper J., Seuberlich T., Oevermann A. & Schweizer-Gorgas D. 2020. Correlative magnetic resonance imaging and histopathology in small ruminant listeria rhombencephalitis. Frontiers in Neurology. 11: 518697.

Riet-Correa G., Duarte M.D., Barbosa J.D., Oliveira C.M.C., Cerqueira V.D., Brito M.F. & Riet-Correa F. 2006. Meningoencefalite e polioencefalomalacia causadas por Herpesvírus bovino-5 no Estado do Pará. Pesquisa Veterinária Brasileira. 26: 44-46.

Sant’Ana F.J.F., Nogueira A.P.A., Souza R.I.C., Cardinal S.G., Lemos R.A.A. & Barros C.S.L. 2009. Polioencefalomalacia experimental induzida por amprólio em ovinos. Pesquisa Veterinária Brasileira. 29: 747-752.

Scarratt W.K., Collins T.J. & Sponenberg D.P. 1985. Water deprivation-sodium chloride intoxication in a group of feeder lambs. Journal of the American Veterinary Medical Association. 186: 977-978.

Schenk H.C., Ganter M., Seehusen F., Schroeder C., Gerdwilker A., Baumgaertner W. & Tipold A. 2007. Magnetic Resonance Imaging Findings in Metabolic and Toxic Disorders of 3 Small Ruminants. Journal of Veterinary Internal Medicine. 21: 865-871.

Silva A.M., Flores E.F., Weiblein R., Botton S.A., Irigoyen L.F., Roehe P.M., Brum M.C.S. & Canto M.C. 1998. Infecção aguda e latente em ovinos inoculados com o herpesvírus bovino tipo 5 (BHV-5). Pesquisa Veterinária Brasileira. 18: 99-106.

Thornber E.J., Dunlop R.H., Gawthorne J.M. & Huxtable C.R. 1979. Polioencephalomalacia (cerebrocortical necrosis) induced by experimental thiamine deficiency in lambs. Research in Veterinary Science. 28: 378-380.

Tsuka T., Taura Y., Okamura S., Tamura H., Okamoto Y., Okamura Y. & Minami S. 2008. Imaging diagnosis - polioencephalomalacia in a calf. Veterinary Radiology & Ultrasound. 49: 149-151.

Underwood W.J., Blauwiekel R., Delano M.L., Gillesby R., Mischler S.A. & Schoell A. 2015. Biology and Diseases of Ruminants (Sheep, Goats, and Cattle). Laboratory Animal Medicine. 2015: 623-694. DOI: 10.1016/B978-0-12-409527-4.00015-8

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How to Cite

Cerri, F. M., Cardoso, I. M. Z. C., Machado, V. M. de V., Oliveira-Filho, J. P. de, Amorim, R. M., Borges, A. S., & Andrade, D. G. A. de. (2022). Polioencephalomalacia in Sheep - Clinical and Magnetic Resonance Imaging Findings. Acta Scientiae Veterinariae, 50. https://doi.org/10.22456/1679-9216.121094

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