Seizures – Diagnosis
A thorough medical history is extremely important, including a complete and accurate description of the episodes. Have the owner describe the events in detail, including an in-depth description of exactly what they saw, as well as the frequency, duration, time of day, and presence of lateralizing signs. Ask the owner if there are any abnormalities after the episode or if there is an abrupt cessation of the episode. Post-ictal abnormalities separate seizures from other paroxysmal episodes. Ask the owner if there are any abnormalities between episodes. Inter-ictal abnormalities are indicative of symptomatic epilepsy. Other important information to obtain include: familial history, past injuries or illnesses, exposure to potential seizure-inducing toxins, exposure to human or pet medications, past and current medication history, vaccination status, and travel history. If it is still unclear whether the episodes are seizures, have the owner video an episode for review.
As always, a complete neurological examination should be performed. Use caution in interpreting neurologic abnormalities during the post-ictal period. Patients in the post-ictal period may have an absent menace response OU and/or be blind for 2-3 days (up to 1 week in rare cases), be mentally dull or disoriented, demonstrate paresis or ataxia, and may have postural reaction deficits. Patients already being given anticonvulsants, especially phenobarbital and KBr, may display sedation/lethargy, symmetrical postural reaction deficits, or weakness/ataxia. Asymmetry of abnormalities is suggestive of intracranial disease, but caution is still advised during the post-ictal period not to over interpret neurologic exam findings.
After obtaining a thorough history and performing a complete neurological exam, you should ask yourself two questions:
- Is this patient truly having seizures? Many other paroxysmal episodes can easily be misinterpreted as seizures (see Paroxysmal Disorders table below).
- If yes, where is the cause of the seizures?
The minimum database for all patients having seizures includes:
- Complete blood count (CBC), serum biochemical profile, and urinalysis to screen for metabolic causes of seizures.
- Pre- and post-prandial bile acids – This should be performed even in patients with “normal” biochemical profile results because some patients with portosystemic shunt (PSS) or Microvascular Dysoplasia (MVD) have normal liver enzyme values. It should also be performed prior to starting phenobarbital and other anticonvulsants that are metabolized by the liver to get a baseline before starting medication.
- Lead level – Lead-based paint was discontinued in the USA in 1978. There are still many other sources of lead to which animals are exposed, including old houses with lead-based paint (especially in the northeastern USA), lead in the environment (e.g., lead batteries, lead shot, lead-glazed ceramics/china,
pewter, leaded crystal), and imported materials from other countries that have less stringent standards.
- Thyroid hormone analysis – This is recommended in older patients. It is controversial whether hypothyroidism actually causes seizures, but it may exacerbate seizures and make them more difficult to control. Thyroid hormone levels should be measured prior to starting phenobarbital since this medication can lower thyroid hormone levels.
There are many causes for seizures that can be characterized as either extracranial or intracranial in origin. When first presented with a patient having seizures, extracranial causes should be ruled out first before assuming that a patient has Idiopathic Epilepsy or any other intracranial disorder. The two primary broad categories of extracranial causes of seizures are metabolic disease (e.g., portosystemic shunt, hypoglycemia) and toxin exposure. See the table at right for additional causes.
Intracranial causes of seizures
Once extracranial causes have been ruled out, then intracranial causes should be considered. Patients with Idiopathic Epilepsy (IE) typically start having seizures between 1-5 years of age. It is acceptable and reasonable to begin an anticonvulsant and monitor the patient if it is a “typical” breed for IE, starts having seizures between 1-5 years of age, is normal during the inter-ictal periods, has a normal neurological exam, and has no identifiable extracranial cause for seizures. Remember, however, that patients with structural intracranial disease (e.g., brain tumor, encephalitis) may be presented with seizures as the only client complaint. As such, it is never wrong to pursue imaging and/or CSF analysis to rule out other intracranial diseases that require treatment other than anticonvulsants.
Advanced imaging (MRI > CT) +/- spinal fluid analysis is recommended for patients in the following categories:
- Seizure onset at less than 1 year of age or greater than 5 years of age
- All small/toy breed dogs due to the increased prevalence of GME & Necrotizing Encephalitis, especially the following breeds: Pug, Maltese, Chihuahua, Shih Tzu, Yorkies
- All cats. Although Idiopathic Epilepsy occurs in cats, other diseases are more common.
- Abnormalities noted by the owner during the inter-ictal period (e.g., behavior change, circling, pacing, visual deficits, inappropriate elimination)
- Abnormalities detected on neurological exam during the inter-ictal period
Other diagnostics may be indicated, such as infectious disease testing or electroencephalography.
Whenever faced with a patient that is being presented for possible seizures, ask yourself whether the patient is truly having seizures. While the owners’ thoughts on the subject are important, owners frequently interpret all episodes as seizures. Get a complete and accurate description of the episode before making a judgment call. If the patient is not clearly having seizures, be sure to consider the paroxysmal episodes listed at right.Last updated by NeuroPetVet on December 17, 2017.