Joe Mayhew - Large Animal Neurology

The client should be encouraged to keep an accurate diary of known and suspected seizure episodes particularly noting preictal signs, site on the body where the motor disturbance begins, and the severity and timed duration of each seizure. This will allow a best prediction as to whether the epilepsy is stable, resolving or progressing, to be made. Should individual seizures be occurring say fewer than one every month and the patient does not injure itself to require veterinary attention, then medication is probably not indicated. If there are cluster seizures, status epilepticus or more than one seizure a month, or if the patient injures itself to require veterinary attention and the client does not accept euthanasia as an option, then anticonvulsant therapy must be considered.

For acute control of seizures in adult horses, IV glucose should be administered if hypoglycemia is suspected. Then, 50 mg IV doses of diazepam or midazolam can be used. 32, 33Benzodiazepine drugs should not be left in a plastic container or syringe for more than a few minutes as they may become inactivated. If diazepam or an alternative benzodiazepine drug is not available, then standard doses of alpha‐2 agonist drugs, or IV levetiracetam can be used. If these are ineffective, then general anesthesia is indicated and at this stage euthanasia must be strongly considered. Midazolam can also be considered as first line therapy for neonatal seizures in foals, 32,34and intranasal equivalent doses may expedite seizure control. 35

Pharmacokinetic and related drug disposition studies on phenobarbital, 36–39potassium bromide 40,41and phenytoin in horses, 42–44potassium bromide in sheep, 45and phenobarbital 46and levetiracetam in foals have been published. Gabapentin, 48pregabalin, 49and imepitoin 50may need to be considered if the starting drugs are ineffective at giving some seizure control. Several other human anticonvulsant drugs may be worth considering if control of seizures is unsatisfactory. Two drugs that have been tried in foals with unsubstantiated anticonvulsant results are carbamazepine (a sodium channel stabilizer) at 250–500 mg doses and triazoline (an excitatory amino acid antagonist) at 1 g doses. Discussions on the use of antiseizure medication in small animals 51and in humans 52are useful resources to consult.

1 1 Novales M, Hernandez E and Lucena R. Electrocution in the horse. Vet Rec 1998; 142(3): 68.

2 2 Lowrie M and Garosi L. Classification of involuntary movements in dogs: paroxysmal dyskinesias. Vet J 2017; 220: 65–71.

3 3 Caraballo RH, Cersosimo RO and Fejerman N. Benign focal seizures of adolescence: a prospective study. Epilepsia 2004; 45(12): 1600–1603.

4 4 Fejerman N. Nonepileptic disorders imitating generalized idiopathic epilepsies. Epilepsia 2005; 46(Suppl 9): 80–83.

5 5 van den Broek AH and Huntley JF. Sheep scab: the disease, pathogenesis and control. J Comp Pathol 2003; 128(2–3): 79–91.

6 5bMiller, S. M. (2020). Putative Otobius megnini‐associated clinical signs in horses in South Africa (2012–2018). J S Afr Vet Assoc, 91(0), e1–e6. 10.4102/jsava.v91i0.1983

7 6 Mayhew IG, Jolly RD, Burnham D, et al. Familial episodic ataxia in lambs. N Z Vet J 2013; 61(2): 107–110.

8 7 Dittmer KE, Jolly RD, Mayhew IG, et al. Familial episodic ataxia in lambs is potentially associated with a mutation in the fibroblast growth factor 14 (FGF14) gene. PLoS ONE 2017; 12(12): e0190030.

9 8 Wong M. Advances in the pathophysiology of developmental epilepsies. Semin Pediatr Neurol 2005; 12(2): 72–87.

10 9 Blumenfeld H. Impaired consciousness in epilepsy. Lancet Neurol 2012; 11(9): 814–826.

11 10 Chigerwe M and Aleman M. Seizure disorders in goats and sheep. J Vet Intern Med 2016; 30(5): 1752–1757.

12 11 Lacombe VA. Seizures in horses: diagnosis and classification. Vet Med Auckl 2015; 6: 301–308.

13 12 Hardefeldt LY. Hyponatraemic encephalopathy in azotaemic neonatal foals: four cases. Aust Vet J 2014; 92(12): 488–491.

14 13 Lacombe VA, Mayes M, Mosseri S, et al. Epilepsy in horses: aetiological classification and predictive factors. Equine Vet J 2012; 44(6): 646–651.

15 14 Lacombe VA, Mayes M, Mosseri S, Reed SM and Ou TH. Distribution and predictive factors of seizure types in 104 cases. Equine Vet J 2014; 46(4): 441–445.

16 15 Braun U, Schweizer G and Hilbe M. Epileptiform convulsions in a cow with degeneration of the hippocampus. Vet Rec 2002; 150(9): 281–282.

17 16 Galvin N and Collins D. Perinatal asphyxia syndrome in the foal: review and a case report. Ir Vet J 2004; 57(12): 707–714.

18 17 Toribio RE. Equine neonatal encephalopathy: facts, evidence, and opinions. Vet Clin North Am Equine Pract 2019; 35(2): 363–378.

19 18 Viu J, Monreal L, Jose‐Cunilleras E, et al. Clinical findings in 10 foals with bacterial meningoencephalitis. Equine Vet J 2012; Suppl(41): 100–104.

20 19 Finno CJ. Equine Familial Isolated Hypocalcemia (EFIH). 2020. Retrieved 2022_02_28 from: https://vgl.ucdavis.edu/test/efih

21 20 Loynachan AT, Williams NM and Freestone JF. Kernicterus in a neonatal foal. J Vet Diagn Invest 2007; 19(2): 209–212.

22 21 Aleman M, Costa LR, Crowe C and Kass P H. Presumed neuroglycopenia caused by severe hypoglycemia in horses. J Vet Intern Med 2018.

23 22 Aleman M, Finno C J, Weich K and Penedo MCT. Investigation of known genetic mutations of Arabian horses in Egyptian Arabian foals with juvenile idiopathic epilepsy. J Vet Intern Med 2018; 32(1): 465–468.

24 23 Lichter‐Peled A, Polani S, Stanyon R, Rocchi M and Kahila Bar‐Gal G. Role of KCNQ2 and KCNQ3 genes in juvenile idiopathic epilepsy in Arabian foals. Vet J 2013; 196(1): 57–63.

25 24 Page P, Parker R, Harper C, Guthrie A and Neser J. Clinical, clinicopathologic, postmortem examination findings and familial history of 3 Arabians with lavender foal syndrome. J Vet Intern Med 2006; 20(6): 1491–1494.

26 25 Manso‐Diaz G, Dyson SJ, Dennis R, et al. Magnetic resonance imaging characteristics of equine head disorders: 84 cases (2000–2013). Vet Radiol Ultrasound 2015; 56(2): 176–187.

27 26 van der Ree M and Wijnberg I. A review on epilepsy in the horse and the potential of Ambulatory EEG as a diagnostic tool. Vet Q 2012; 32(3–4): 159–167.

28 27 Reed SM, Furr M, Howe DK, et al. Equine protozoal myeloencephalitis: an updated consensus statement with a focus on parasite biology, diagnosis, treatment, and prevention. J Vet Intern Med 2016; 30(2): 491–502.

29 28 Vanschandevijl K, Gielen I, Nollet H, et al. Computed tomography‐guided brain biopsy for in vivo diagnosis of a cholesterinic granuloma in a horse. J Am Vet Med Assoc 2008; 233(6): 950–954.

30 29 Madigan JE, Valberg SJ, Ragle C and Moody JL. Muscle spasms associated with ear tick (Otobius megnini) infestations in five horses. J Am Vet Med Assoc 1995; 207(1): 74–76.

31 30 McEntee M, Summers BA, de Lahunta A and Cummings J. Meningocerebral hemangiomatosis resembling Sturge‐Weber disease in a horse. Acta Neuropathol Berl 1987; 74(4): 405–410.

32 31 Pirie RS, Mayhew IG, Clarke CJ and Tremaine WH. Ultrasonographic confirmation of a space‐occupying lesion in the brain of a horse: choroid plexus papilloma. Equine Vet J 1998; 30(5): 445–448.

33 32 Hubbell JA, Kelly EM, Aarnes TK, et al. Pharmacokinetics of midazolam after intravenous administration to horses. Equine Vet J 2013; 45(6): 721–725.

34 33 Wilkins PA. Hypoxic ischemic encephalopathy: neonatal encephalopathy, in Recent Advances in Equine Neonatal Care Wilkins PA. 2003. International Veterinary Information Service. Retrieved 2022_02_28 from https://www.ivis.org/library/recent‐advances‐equine‐neonatal‐care/hypoxic‐ischemic‐encephalopathy‐neonatal

35 34 Wilkins PA. How to use midazolam to control equine neonatal seizures. 51st Annl Conv Am Assoc Eq Pract. Seattle, WA. 2005. Retrieved 2022_02_28 from https://www.ivis.org/library/aaep/aaep‐annual‐convention‐seattle‐2005/how‐to‐use‐midazolam‐to‐control‐equine‐neonatal‐seizures