A diagnosis of epilepsy is not made by a single test. It is a process of elimination — ruling out other causes of seizures before arriving at a diagnosis. Understanding what each step is for can make the process less overwhelming and help you have more productive conversations with your vet.

Step 1 — Rule out reactive causes

Before considering epilepsy, your vet will typically want to rule out conditions that cause an otherwise normal brain to seize. These are called reactive seizures, and the most common causes include low blood sugar (hypoglycemia), liver disease, kidney disease, electrolyte imbalances, and toxin exposure. A basic blood panel and urinalysis can identify most of these. If a reactive cause is found and treated, seizures often stop without any epilepsy treatment.

Step 2 — Consider the patient profile

Age at first seizure onset is one of the most informative pieces of information in the diagnostic workup. According to the IVETF consensus diagnostic guidelines, dogs who have their first seizure between 6 months and 6 years of age are much more likely to have idiopathic (genetic) epilepsy. Dogs outside this age range — particularly those over 6 years — are more likely to have a structural cause, such as a brain tumor or inflammatory disease, and require more advanced investigation.

Step 3 — MRI of the brain

Magnetic resonance imaging (MRI) is considered the preferred imaging modality for identifying structural brain disease. It is typically recommended for dogs outside the 6-month to 6-year age window, those with abnormal neurological examinations, those experiencing cluster seizures or status epilepticus at first presentation, or those who do not respond to anti-seizure medication. MRI requires general anesthesia in veterinary patients.

Step 4 — Cerebrospinal fluid (CSF) analysis

CSF analysis — sometimes called a "spinal tap" — involves collecting a small amount of fluid from around the spinal cord while the animal is under general anesthesia (typically at the same time as MRI). It looks for evidence of inflammation, infection, or cancer affecting the central nervous system. It is often performed alongside MRI when a structural or inflammatory cause is suspected.

A diagnosis of idiopathic epilepsy

If blood work is normal, MRI (when performed) shows no structural abnormality, and CSF analysis is unremarkable, your vet may conclude that your pet has idiopathic epilepsy — epilepsy with no identifiable cause other than a suspected genetic predisposition. This is the most common diagnosis in young to middle-aged dogs and, while it requires management, is generally considered the most favorable epilepsy diagnosis in terms of long-term outlook.