Evidence of neuronal loss and granule cell axon reorganization in the dentate gyrus of cats with temporal lobe epilepsy-like seizures

Objective: To determine whether some cats with epilepsy and temporal lobe epilepsy (TLE)-like seizures have dentate gyrus neuropathologic changes consistent with TLE, including hilar neuron loss and mossy fiber sprouting. Methods: Postmortem hippocampal tissue from 5 cats with a history of seizures and 6 control cats was evaluated. Nissl-stained sections were used to estimate hilar neuron populations within the dentate gyrus by optical fractionator stereology. Timm-stained sections were scored by masked investigators to assess mossy fiber sprouting. Hippocampi from epileptic cats were evaluated bilaterally, and findings were compared with control cats. Results: Mean hilar neuron counts were lower in epileptic cats than controls, although this difference was not statistically significant. Two epileptic cats had hippocampal hilar neuron counts more than 2 SDs below the control mean. Mean Timm scores were higher in epileptic cats than controls, and 2 epileptic cats had mossy fiber sprouting scores more than 2 SDs above the control mean. One epileptic cat had both marked left-sided hilar neuron loss and severe mossy fiber sprouting, greatest in the left hippocampus. Conclusions: The study found that 1 epileptic cat with TLE-like seizures had dentate gyrus neuropathologic changes resembling those described in TLE in humans and other animal models. Clinical Relevance: These findings support naturally occurring feline TLE as a potential clinical entity, and antemortem diagnostics should be investigated to identify these cats for advanced treatment options, such as surgical or laser ablation of the affected hippocampus.