Subclinical lumbar polyradiculopathy in aged domestic, laboratory, and exotic mammalian species--a light and selected electron microscopic study.

Lumbar polyradiculopathy, characterized by ballooning myelin sheaths and axonal distortion, was documented in multiple, aged, domestic, laboratory, and exotic mammalian species. Animals studied that exhibited this nerve rootlet change included the goat, sheep, pig, white-tailed deer, gerbil, vole, ferret, beaver, hedgehog, chinchilla, North Chinese leopard, lion, cheetah, mountain lion, llama, East African eland, Uganda giraffe, polar bear, and drill. Ultrastructurally, lumbar nerve rootlets from the North Chinese leopard revealed prominent and often multiple lamellar separations in the area of myelin bubbling. Clefts in myelin sheaths contained macrophages with engulfed fragments of myelin. Axons were sometimes variously attenuated, and the axoplasm contained densely packed neurofilaments. In all species, the lesion was subclinical and considered an incidental age-related finding.