Summary
On initial evaluation for onset of seizure disorders at nonreferral veterinary practices, 50 previously healthy dogs were enrolled in a study to determine the probability of identifying a specific cause for the seizures. Treatment was not administered prior to entry of dogs in the study. On the basis of antemortem and postmortem test results, 22 dogs (44%) were classified as having primary epileptic seizures (pes; idiopathic or without identifiable cause), 23 (46%) had secondary epileptic seizures (ses; identifiable intracranial cause), and 5 (10%) had reactive epileptic seizures (res; metabolic or transient noxious cause). Forty-one dogs (82%) had 2 or more seizures before evaluation, with 37 (90%) of these dogs classified as having epilepsy on the basis of an underlying chronic brain disorder. For these 41 dogs, 17 (41%) had pes, 20 (49%) had ses, and 4 (10%) had res. Among the 9 dogs (18%) with nonrecurring seizures, 5 had pes, 3 had ses, and 1 had res. Generalized seizures were the most common first-observed seizure type associated with all etiologic classifications in all dogs with recurring and nonrecurring seizures.
Diagnosis of ses was statistically more probable when the dog was less than 1 or more than 7 years old at the first seizure, when the first seizure was a partial seizure, or when the first seizure occurred between midnight and 8 am. A diagnosis of res was statistically more probable only when the interval between the first and second seizure was brief (≤ 4 weeks). A diagnosis of pes was statistically more probable when the dog was between 1 and 5 years of age at the first seizure, when the dog was a large breed (> 15 kg), when the seizure occurred between 8 am and midnight, or when the interval between the first and second seizure was long (> 4 weeks).
