In 2015, the International Veterinary Epilepsy Task Force (IVETF) published a list of criteria to diagnose idiopathic epilepsy in dogs (not cats). The IVETF consisted of a group of veterinary neurologists, neuropathologists, and epileptologists. If you wish to see all of the resulting publications, just let me know! (They are available open access.)

The IVETF listed several ways to make a diagnosis of idiopathic epilepsy, starting with the lowest level of confidence (Tier I) and rising to the top with the most confidence in the diagnosis (Tier III). When using this information in your daily practice, consider writing "diagnosis: idiopathic epilepsy with Tier 1 confidence" in the medical record when a patient meets the criteria for a Tier I diagnosis of idiopathic epilepsy.

Please note, idiopathic epilepsy does not mean, any seizure disorder. Idiopathic epilepsy is a specific disease, that causes repeated seizures. ANY animal with repeated seizures can be diagnosed with epilepsy, but idiopathic epilepsy is ONE form of epilepsy. Make sense?

Tier I:

A dog must have:

A history of 2 or more seizures at least 24 hours apart
Have the age at onset between 6 months and 6 years
Demonstrate a normal inter-ictal physical and neurologic examination
A normal CBC, and serum biochemistry (the IVETF lists what they consider to be standard in a serum biochemistry analysis. Let me know if you want/need this list.)
A normal fasting bile acids and/or ammonia
A normal urinalysis
A familial history of IE is supportive, but not required

Tier II:

To diagnose idiopathic epilepsy with Tier II level confidence a dog must have:

All of Tier I plus...
A normal brain MRI
A normal CSF analysis
Normal fasting and post-prandial bile acids

Tier III:

All of Tier II plus...
Identification of ictal or inter-ictal EEG abnormalities suggestive of seizure disorders.

So, if a patient meets Tier I level confidence, when should MRI be performed?

Anytime a client wishes to confirm a diagnosis of intracranial disease. (This includes idiopathic epilepsy which is diagnosed by exclusion of other causes)
If a dog has a seizure onset of < 1 year or > 7 years of age (according to the IVETF)
If neurologic abnormalities reflective of the prosencephalon/forebrain are identified on the neurologic examination regardless of age, breed or a familial history of seizures.

In summary, it is always worthwhile to inform clients of the option of MRI when their dog (or cat) has seizures however, if the Tier I criteria are met and MRI has a high likelihood of normal results, it is very reasonable to skip this test and begin treatment for idiopathic epilepsy.

I try to remember that MRI abnormalities were identified in 22% of dogs with a normal neurologic exam and 90% of dogs with an abnormal neurologic examination in one study.

What about CSF analysis, you ask? I'm glad you asked! Some dogs with meningitis will have a normal MRI, therefore an MRI PLUS CSF tap is often my recommendation to ensure we don't overlook those patients inappropriately by just performing an MRI.

What about cats? The IVETF recommendations do not specifically apply to cats however many neurologists, including me, extrapolate this information to cats in practice. My fingers and toes are crossed for science driven cat-specific recommendations in the near future.

Have a great week! As always stay safe, and let me know how I can help you, help your patients, with neurologic disease.