Exotis ISSN 2398-2985

Guinea Pigs

Seizures

Synonym(s): Epilepsy

Contributor(s): Cathy Johnson-Delaney, Anna Meredith

Introduction

  • Cause: extracranial and intracranial causes. Severe pain may elicit a seizure. Severe pruritis as with lice and mite infestations has caused seizures. Electric shock from chewing on electric cords. A seizure may also be an agonal sign.
  • Signs: vary depending on underlying cause.
  • Diagnosis: full physical examination, including oral dental examination and otoscopic examination. CBC/serum chemistries. If any exudates are present, culture and sensitivity and cytology. For LCMV: PCR, IFA and serology. Blood lead if lead toxicity suspected. Cholinesterase testing if organophosphate toxicity suspected. Radiography, CT, MRI. CSF analysis. Electroencephalogram, however normal values not established.
  • Treatment: control active seizure with benzodiazepines. Some may require the addition of phenobarbital. For long-term management some may need phenobarbital or potassium bromide. General supportive care, including fluid therapy and nutritional support. Other treatments dependent on etiology, but can include administration of dextrose, mannitol, systemic antibiotics. Steroid use is controversial in guinea pigs and is usually avoided if infection is suspected. It could be used if there is cerebral edema.
  • Prognosis: depends on etiology. Seizures can reoccur even if underlying cause is resolved as a ‘seizure focus’ (scar tissue?) in the brain may have developed. Poor to grave prognosis: status epilepticus, particularly if it cannot be medically controlled. Grave if agonal.
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Pathogenesis

Etiology

  • Extracranial causes:
    • Metabolic imbalances such as hypoglycemia, pregnancy toxemia, hepatic disease, hypocalcemia, severe uremia, electrolyte imbalances, heatstroke. Pregnancy toxemia, Polydipsia/polyuria, Heat stress.
    • Toxins: organophosphates, lead, strychnine, pesticides, overdosing of metronidazole.
    • Nutritional: Vitamin E deficiency Muscular dystrophy: nutritional, starvation (usually secondary to severe dental disease Dental disease.
    • Infectious: parasitic infection with lice or mites, particularly with severe pruritis, cause seizures. The mechanism is unknown.
  • Intracranial causes:
    • Neoplastic: CNS lymphosarcoma, or any CNS primary or metastatic neoplasm.
    • Infectious/inflammatory:
      • Encephalitis:
        • Viral: LCMV, Rabies.
        • Protozoal: toxoplasmosis; ask the owner if they have cat(s), if the guinea pig has access to the litter area.
        • Bacterial: Streptococcus pneumonia, Pasteurella multocida, Staphylococcus aureus. May have started in respiratory tract Pneumonia or due to otitis Otitis exterma/media/interna.
    • Trauma: head injury.
  • Vascular: infarct in the brain secondary to cardiac disease. May be difficult to detect antemortem. Cardiac evaluation including echocardiogram and ECG may be indicated.
  • Idiopathic: epilepsy; this is usually the diagnosis after all other causes ruled out.

Predisposing factors

General

  • Dental disease, malocclusion. May be because of inadequate diet, orbecause of it, the guinea pig cannot eat the appropriate foods and nutritional deficiencies lead to metabolic disturbances.
  • Upper respiratory infection, otitis interna/media can extend into the brain.
  • Pregnancy toxemia can develop that includes hypoglycemia, hyperglycemia, hypocalcemia which precipitate seizures.
  • Cardiac disease can be involved in precipitation of clots and emboli, that may cause infarcts in CNS.

Pathophysiology

  • Seizures are due to brain dysfunction in the cerebrum.
  • A seizure is defined as a sudden, uncontrolled, transient increase in electrical discharge in the brain.
    • This results in an alteration or loss of consciousness.
    • Altered muscle tone including twitching.
    • There may be jaw movements like chewing.
    • There may be urination, defecation, salivation.
  • Grand-mal seizures (generalized) are tonic-clonic.
    • Muscle tone extremely increased (tonus) alternating usually quickly with relaxation (clonus).
    • Paddling of the limbs with the guinea pig lying on its side.
    • This is the most common form seen in guinea pigs.
  • Partial motor seizures are characterized by asymmetrical signs, focal twitching, isolated tonic-clonic movements of just the facial muscles or limbs.
  • There are classically 3 phases to a seizure. It may be difficult to identify or recognize these in some guinea pigs.
  • Pre-ictal (aura):
    • Restlessness, anxious, hyperexcitable (jump at small sounds), appears to look at non-existent things, may vocalize with sounds associated with nervousness.
    • May not have been noticed, or may last for several minutes.
  • Ictal:
    • Usually only 1-2 min.
    • Owner usually perceives it as much longer.
    • Loss of consciousness.
    • Fall over, may paddle, twitch, make chewing/jaw movements.
    • May urinate, defecate.
    • Some may vocalize.
  • Post-ictal:
    • Period following the seizure.
    • Seems disoriented, stuporous.
    • May not recognize owner or surroundings.
    • Can have vision defects, circle, head press or other behavior changes.
    • May last for minutes to hours.
  • Excessive discharges in aggregates of neurons occur from an area of the brain that is designated as a 'seizure focus' and is where the seizure originates from.
    • Abnormal electrical impulses from this spread to other parts of the brain which cause the activity associated with the seizure.
    • There can be a single or multiple foci in the brain. They can fire separately or simultaneously.
    • A seizure event changes the electrical charges within the brain - lowering the threshold for nerves to depolarize. This makes it easier for additional seizures to start in close proximity to the original source.
    • This localization of foci can be done using EEG, although this is rarely done in pet guinea pigs.

Timecourse

  • Depends on etiology.
  • A seizure itself is a peracute event.

Epidemiology

  • Lice and mites are easily transmitted between guinea pigs and clearing the environment may be difficult.
  • LCMV is usually due to exposure to wild rodents. A colony infected with LCMV may be culled as it is a zoonotic disease.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Lichtenberger M, Richardson J A (2008) Emergency care and managing toxicoses in the exotic animal patient. Vet Clin Exot Anim 11 (2), 211-228 PubMed.

Other sources of information

  • Mayer J (2013) Rodents. In: Exotic Animal Formulary. 4th edn. Eds: Carpenter J W, Marion C J. Elsevier. pp 476-516.
  • Hawkins M G & Bishop C R (2012) Disease Problems of Guinea Pigs. In: Ferrets, Rabbits and Rodents Clinical Medicine and Surgery. 3rd edn. Eds: Quesenberry K E & Carpenter J W. Elsevier. pp 295-310.
  • Antinoff N (2011) Seizures. In: Blackwell's Five-Minute Veterinary Consult: Small Mammal. Ed: Oglesbee B L. Wiley-Blackwell. pp 326-328.
  • Harkness J E, Turner P V, Vandewoude S & Wheler C L (2010) Harkness and Wagner’s Biology and Medicine of Rabbits and Rodents. 5th edn. Wiley-Blackwell. pp 214-216
  • Hrapkiewicz K & Medina L (2007) Clinical Laboratory Animal Medicine an Introduction. 3rd edn. Blackwell Publishing. pp 152-177.


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