Neurotoxicity of intrathecally administered tetracaine commences at the posterior roots near entry into the spinal cord

Background and Objectives: Neurotoxicity of intrathecally administered loca l anesthetics is generating increased interest. This study was designed to examine the histopathologic effects of intrathecally administered tetracain e. Methods: Sixty Wistar rats randomly received either 20%, 10%, 5%, 3%, 1%, 0 .5%, or 0% tetracaine dissolved in 10% glucose solution or no solution via a chronically implanted intrathecal catheter. The spinal cord at L1, poster ior and anterior roots and cauda equina were excised 5 days later, sectione d, processed, and prepared for light and electron microscopic examinations. Results: Rats treated with tetracaine at 10% or 20% developed lesions in th e posterior white matter and posterior roots. Rats injected with 3% or 5% t etracaine developed lesions, which began in the posterior roots close to th e spinal cord and extended to the posterior white matter. The lesions were characterized by axonal degeneration. Injections of less than or equal to 1 % of tetracaine did not cause any pathological changes. Conclusions: Our results suggest that the initial target of intrathecal tet racaine neurotoxicity may be the posterior roots at their entry into the sp inal cord, where the axons are devoid of myelin sheath and thus representin g a sensitive area for neurotoxic change.