Dogs with idiopathic epilepsy and focal epileptic seizures lack hilar neuron loss and mossy fiber sprouting of temporal lobe epilepsy.

Objective: To evaluate neuropathological changes in dogs with idiopathic epilepsy and history of focal seizures using previously described criteria for temporal lobe epilepsy (TLE) in humans and other animals. Methods: This was a prospective descriptive study. Dogs of any age, sex, or breed with a history of idiopathic epilepsy and focal seizures were included. Immediately following euthanasia, dogs were perfused, and tissue was collected. Brains were sectioned, mounted, and stained. Nissl-stained slides were used for stereology, and Timm stain was used to evaluate for evidence of mossy fiber sprouting. Results: 7 dogs were included in the final analysis. For stereological cell counts evaluating hilar neuron loss, no case was significantly lower in number of neurons. Additional analysis compared right and left to look for asymmetry, and none were significant (P = .259). Using Timm stain to evaluate mossy fiber sprouting, no cases showed extensive sprouting, and no asymmetry was detected between left and right hippocampi (P = .054). Conclusions: In our cohort, while there were changes associated with seizures detected within the hippocampi, none were severe or consistent enough to qualify as TLE using the human criteria. Clinical Relevance: Our study focused on dogs with focal seizures as their main seizure presentation as that is the most common semiology in people with TLE. However, a future study could consider evaluating the neuropathology of dogs with asymmetric hippocampi detected on MRI. If TLE can be shown in dogs, then advanced treatment options, such as surgery or laser ablation, could be considered in refractory patients.