Intrathecal 2% Tetracaine Causes Mild Histological Lesions in the Spinal Cord without Detectable Sensory Deficits on Paw Stimulation Test in Rats

The purpose of this study is to determine if intrathecal 2% tetracaine (TC) causes histological changes by its neurotoxicity, and to examine the relationship between the lesions and neurological functions. Twenty-two rats received either 2% TC or 0% TC dissolved in 10% glucose, via an intrathecal catheter terminated at T 13 level. Neurological deficits were evaluated by rat's behavior and paw stimulation test (UCSF). Five days after drug administration, the L l spinal cord with the anterior and posterior roots and cauda equina were excised for light and electron microscopy. Four rats out of 8 in 2% TC group showed mild pathological changes induced by neurotoxicity mainly in the posterior roots and slightly in the posterior column. However, there were no significant differences in sensory and behavioral function between the rats who had received 2% TC with lesion and the others with no lesion. As many rootlets enter one segment of the spinal cord, mild and restricted lesions may be difficult to detect by sensory tests. These findings may explain the fact that the patients with transient neurologic symptoms (TNS) are normal by neurological tests.