Local anesthetic: Transient neurologic symptoms

Lidocaine was first used as a spinal anesthetic in 1948. In 1991, case reports of cauda equina syndrome began to appear following the use of 5% lidocaine through microcatheters. Two years later,in 1993, transient neurologic symptoms (TNS), was described. TNS is a painful condition of thebuttocks and thighs with possible radiation to the lower extermities, beginning as soon asa few hours after spinal anesthesia and lasting as long as ten days. Pain can be mild to severe. However, unlike in cauda equina syndrome,TNS isexclusivelya pain syndrome– there is no bowel or bladder dysfunction, and neurologic, MRI , and electrophysiologic examinations are normal.

Alllocal anesthetics can cause TNS. The incidence of TNS following lidocaine is 1:7 (13%). The relative risk of TNS when using lidocaine (versus bupivacaine, mepivacaine, prilocaine, or procaine) is 4.35, based on an analysis of 14 studies including 1347 patients. However, mepivacaine risk is about equal to lidocaine, thusthe relative risk of lidocaine/mepivacaine is 7x that of bupivacaine, prilocaine, and procaine. Of note, none of the patients in this study reported permanent neurologic deficits.

Transient Neurologic Symptoms (TNS)

• Incidence:one in sevenlidocaine/mepivacaine intrathecal administrations (7-fold less for bupivacaine, prilocaine, and procaine)
• Associations:alllocal anesthetics
• Timing: few hours to ~ 1 day, lasting up to 10 days
• Symptoms:exclusively painin buttocks, thighs, legs, no dysfunction

Lidocaine is often chosen for neuraxial anesthesia because it has rapid onset, dense blockade, and short duration of action. However, it is also unique in its propensity to cause a phenomenon known as transient neurologic symptoms (TNS). TNS is characterized by pain in the buttocks and legs that develops within a few hours and up to 24 hours after anesthesia. Symptoms typically do not last beyond 2 days. It is important to note that although lidocaine is more likely to cause transient neurologic symptoms than bupivacaine, prilocaine, and procaine, these drugs are less suitable for ambulatory patients due to their prolonged action. Mepivicaine results in TNS at a similar rate as lidocaine. 2-chloroprocaine (which fell out of favor, but seems to be making a comeback) does not and therefore may be a good alternative.