section name header

Basics ⬇

Outline

BASICS

Definition!!navigator!!

Seizures are paroxysmal, transient electrical disturbances of brain function that have a sudden onset, cease spontaneously, and tend to recur.

Pathophysiology!!navigator!!

  • Seizures are caused by excessive neuronal excitation or loss of neuronal inhibition
  • Horses almost always have a focal onset that may secondarily generalize. Often secondary to trauma (which can have occurred a long time previously) or diseases or toxins that have an effect on neuronal function
  • Classic idiopathic epilepsy has not been reported in this species

Systems Affected!!navigator!!

CNS, trauma to other systems from seizure, systems affected by the initiating disease.

Genetics!!navigator!!

Juvenile epilepsy in Arabian foals is likely to have a genetic basis.

Incidence/Prevalence!!navigator!!

Low prevalence.

Signalment!!navigator!!

More likely in adult horses. A benign form of juvenile epilepsy can occur in young growing Arabian foals of Egyptian lineage up to 12 months of age.

Signs!!navigator!!

Historical Findings

A history of trauma or toxin exposure rarely reported.

Physical Examination Findings

  • Seizures are classified as generalized, partial, or partial with secondary generalization
  • In horses, the most common expression of a focal seizure is involuntary movement of facial muscles
  • The onset of a generalized seizure is often preceded by a short period of restlessness and disorientation, as well as inappropriate chewing, teeth grinding, and other bizarre behaviors
  • Subsequently generalized muscular rigidity, recumbency, tonic/clonic paddling movements, salivation, urination, and defecation are common features of a generalized seizure

Causes!!navigator!!

  • Trauma, neoplasm, cholesterol granuloma, hydrocephalus, cerebral abscess, thromboembolism, intracarotid injection, hypoxic–ischemic encephalopathy, hypoxemia, moldy corn poisoning, hepatoencephalopathy, hypoglycemia, hyposmolality, hyperosmolality, and bacterial, viral, verminous, and protozoal encephalitides have all been associated with seizures
  • No other disease process is evident in juvenile epilepsy

Risk Factors!!navigator!!

Exposure to infectious diseases and toxins, etc.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

  • Neuroanatomic diagnostic examination may help localize the site of a seizure focus
  • Cerebrospinal fluid analysis may reveal an underlying infectious process
  • Disease-specific tests may be useful. Advanced imaging may be useful to identify structural lesions

Differential Diagnosis!!navigator!!

  • Diseases causing abnormal movements and loss of consciousness, e.g. heart blocks and sleep disorders
  • Hyperkalemic periodic paralysis and blood electrolyte abnormalities such as hypocalcemia may result in tremors and recumbency but are not associated with loss of consciousness

CBC/Biochemistry/Urinalysis!!navigator!!

No pathognomonic abnormalities.

Imaging!!navigator!!

Advanced imaging is preferable; skull radiographs may reveal fracture lines.

Pathologic Findings!!navigator!!

Dependent on associated disease. Some CNS changes such as hippocampal sclerosis or ischemic neurons may be secondary to the seizures rather than due to the primary disease.

Treatment ⬆ ⬇

Outline

TREATMENT

Treatment of Status Epilepticus!!navigator!!

Control of status epilepticus in adult horses—50 mg IV doses of diazepam. In foals start with a 5 mg diazepam dose. If no benzodiazepines available use standard doses of sedative drugs.

Maintenance Anticonvulsant Therapy!!navigator!!

  • Phenobarbitone at 5 mg/kg SID PO. If unacceptable sleepiness occurs and seizures are not controlled, reduce dose by 20% and add KBr at 25–90 mg/kg SID PO, with or without loading doses of 120–200 mg/kg SID PO for 1–5 days
  • After control, monitor serum concentrations; phenobarbitone therapeutic range 15–40 μg/mL; bromide 1000–4000 μg/mL
  • Long-term administration with anticonvulsants requires the adherence to demanding treatment protocols (see Suggested Reading) and should only be considered after careful discussions with the owner; an apparently stable horse is nevertheless unsafe to ride on medication as breakthrough seizures may occur

Client Education and Prognosis!!navigator!!

  • Severity and frequency of seizure episodes may increase with time and the horse is a danger to himself and his handler during seizuring
  • A horse in anticonvulsant treatment is not safe to be ridden, and a useful guide is that a horse that has had seizures should only be ridden once it has been off medication and seizure free for 6 months
  • Most foals with juvenile epilepsy have a reduction in frequency to cessation of seizures

Medications ⬆ ⬇

MEDICATIONS

Contraindications

Drugs that reduce seizure threshold (e.g. acepromazine). Other drugs such as chloramphenicol or tetracyclines may inhibit hepatic enzymes and prolong the activity of barbiturates.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Abbreviations!!navigator!!

CNS = central nervous system

Suggested Reading ⬆ ⬇

Lacombe VA, Furr M. Differential diagnosis and management of horses with seizures or alterations of consciousness. In: Furr M, Reed S, eds. Equine Neurology, 2e. Ames, IA: Wiley Blackwell, 2015:79–92.

Mayhew IG. Large Animal Neurology, 2e. Oxford, UK: Wiley Blackwell, 2009.

Author(s) ⬆

Author: Caroline N. Hahn

Consulting Editor: Caroline N. Hahn