Neurotoxicity of intrathecal gentamicin: a case report and experimental study.

Distinctive lesions occurred in the brainstem of a 59-year-old patient who had had recent Pseudomonas aeruginosa meningitis treated with parenteral and intrathecal gentamicin sulfate. The lesions were multiple, minute, and discrete, and were characterized by loss of axons, spongiosis, axonal swelling with frequent calcification, loss of astroglia and oligodendroglia, and slight inflammatory response. These lesions were restricted to the myelinated fiber bundles of the pons and mesencephalon. Because similar lesions can occur with other intrathecally administered medications and emboli to the brain, an experimental study in rabbits was done. Similar lesions were produced in normal adult rabbits after a single intracisternal injection of gentamicin sulfate with or without preservative at doses equivalent to 50 and 100 times the human therapeutic dose. Lesions were not seen after injection of normal saline, preservative, or gentamicin sulfate with preservative at doses equivalent to 1 and 10 times the human therapeutic dose. A direct relationship was observed between the cerebrospinal fluid concentrations of gentamicin, brain tissue concentrations of gentamicin, and occurrence of the lesions.