nerve damage as a result of epidural - Transient Neurologic Syndrome

Transient Neurologic Syndrome

Transient Neurologic Syndrome – TNS – is a rare complication of spinal anesthesia characterized by pain in the buttocks, legs and the back. In vast majority of cases it resolves within 24 hours and does not result in long-term damage.

In 1993 the group of researchers from the University of Basel, Switzerland, headed by Dr. Marcus Schneider reported four cases of complicated post-operative period in patients who had gynecological surgery under spinal anesthesia with 5% lignocaine. All of the patients had surgery performed in lithotomy position: lying on the back with the legs lifted in the “stirrups”. Typically, the placement of the needle and the injection of the drug into the subarachnoid space were uneventful. After full recovery from the spinal block, the patients complained of burning, aching pain of varying intensity in the buttocks, thighs and legs. In some patients the pain was constant, in others intermittent. One patient complained of deep pain in the lower back. Neurological examination of the patients did not reveal any abnormalities: the sensation and motor function were unaffected. All patients were given non-steroidal pain killers, and pain disappeared completely after a week. This report heightened already existing concern about the safety of spinal Lignocaine and triggered further research.

Initially this complication was coined as Transient Radicular Irritation, implying the involvement of nerve roots. Later however it was changed to Transient Neurologic Syndrome, or TNS, as this name better reflects the nature of this condition.

Lignocaine was introduced into clinical practice in 1948, and since then literally millions of spinal anesthetics were performed with this drug. The first study on the safety of Lignocaine was published in 1968 in which more than 10,000 of patients received spinal anesthetic were evaluated, more than ninety percent of whom were obstetric. The overall conclusion was that the drug was safe and effective. However 284 patients complained of pain around the area of spinal injection after surgery, and 91 of them refused spinal anesthesia for subsequent surgery because of this pain.

The reports of pain after spinal did not attract much attention, probably because this complication was not severe and there were other, more pressing problems with anesthesia at the time. In 1991 lignocaine came back under scrutiny because of reports of Cauda Equina Syndrome (CES), a devastating complication of spinal anesthesia discussed on the appropriate page of this site. In brief, lignocaine was implicated in 10 out of 11 cases of CES which was also closely associated with the use of spinal microcatheters which are similar to epidural catheters but are smaller in size and are placed into the subarachnoid space for continuous pain relief. At the time it was though that because of a very small diameter of these catheters lignocaine was accumulating in one area around the nerves, so that its concentration could reach toxic levels and cause this complication. Subsequently the Food and Drug Administration of the US banned the use of spinal microcatheters. The incidence of CES dropped, but pain after single dose spinal anesthetic described by Schneider attracted attention this time. As the result of numerous subsequently published case reports and several studies, both clinical and laboratory, this syndrome is well defined and we now know great deal about this complication of spinal anesthesia.

Transient Neurologic syndrome is defined as pain in the lower extremities – buttocks, thighs and legs – after uncomplicated spinal anesthesia and after the spinal block is fully resolve, lasting less than 24 hours. The pain disappears in most patients the next day, though maximum duration is 5 days, and in very rare instances it can last up to 10 days. There are no neurological abnormalities, the sensation and movement are not affected and the reflexes are normal. Pain is usually present on both sides and is most often described by patients as burning, cramping or aching. In about half of patients the pain radiates down their legs, and most also report pain in the lower back.

In the review of 1968 quoted above 294 (2.94%) patients out of 10,000 complained of pain. 91 of them – 0.9% – refused spinals for their next surgery, and it is likely that those patients had more severe form of this complication. According to more recent research the incidence varies greatly, from as low as 1% to as high as 40%. The difference is most likely due to definitions and methodology of research. As with many complications, the harder you look the more likely you are to find it. The patient who had caesarean section may be more concerned with the pain in the operation site and not report mild pain in the legs. However when specifically questioned for the research purposes she will pay attention and report it. What’s important is that the vast majority of reports of TNS come from patients who had their spinal with lignocaine. However, rare cases have been reported with other local anesthetics: mepivacaine, bupivacaine and prilocaine. To my knowledge, no cases of TNS have been reported with the newest local anesthetic ropivacaine.

At this time the mechanism of this complication is not completely clear. Initially it was suggested that the toxicity of local anesthetics is to blame. All local anesthetics in high concentrations are toxic to the nervous tissue, to the point that they have been used for modeling neural damage in laboratory setting, even though the mechanism of this toxicity is not fully understood. The higher the toxicity the more extensive the damage to the nervous cell. The results of animal experiments do show some proof that it may play a role in the development of TNS. In clinical practice, however, the incidence of TNS is the same whether concentration of local anesthetic in the spinal block is 5% or 0.5%, or ten times lower. This theory therefore was dismissed.

Moreover, neither baricity or osmolarity of lignocaine influenced the frequency of TNS. Baricity refers to the relative weight of local anesthetic in relation to the cerebro-spinal fluid. Heavier solutions tend to move down under the force of gravity, and this phenomenon has been used in anesthetic practice to regulate the spread of the block. So that if the operating table is tilted head down the local anesthetic solution spreads towards the patient’s head which results in higher block. Osmolarity refers to the concentration of electrolytes in the mixture.

TNS is rare with epidural anesthesia, and this fact is further testimony to the role of local anesthetic toxicity in this syndrome. It is also possible that the suddenness at which the nerves are exposed to local anesthetic in spinal anesthesia plays a role.

Several risk factors for TNS have been identified. Most patients with more severe forms of TNS had their procedures in the lithotomy position, with legs elevated in the stirrups. This position is widely used in gynecologic surgery for the access to the perineum, as well as in laboring patients. The incidence of TNS after lithotomy position is 30 to 36%, compared to only about 4 to 8% in supine position. Elevating the legs causes the nerves to stretch, and some clinicians believe that this makes the nervous tissue more sensitive to the toxic effects of lignocaine which in turn causes TNS in these patients.

According to the data the risk of TNS is also somewhat higher in patients undergoing knee arthroscopy under spinal anesthesia, where the incidence of this syndrome is 18 to 22%. While this fact is not relevant for the purposes of discussing complications after labor epidural it demonstrates the complexity of the problem for clinicians.

Obesity has been mentioned as another risk factor for TNS. However only one study has found the association, and further research needs to be done to make definite conclusion.

Interestingly, there is data showing that pregnancy may somehow be protective against TNS. In one study 200 patients undergoing caesarean section under spinal anesthetic were randomly assigned to receive either 0.75% Bupivacaine or 5% Lignocaine in their spinals. The patients were interviewed for three consecutive days after surgery to specifically detect the symptoms of TNS. None of the patients in either group had it. After statistically analyzing this data the authors concluded that in worst scenario the incidence of TNS should not exceed 3% with either drug. While lignocaine was implicated in higher occurrence of TNS in other patients, in this study which was done on pregnant women it did not increase the risk. It is plausible that hormonal changes during pregnancy may have protective effect against TNS.

In any case, in current practice lignocaine is seldom used for spinal anesthesia for caesarean section. The main advantage of this drug is fast onset and short duration of action, which makes it very useful for short operations done on outpatient basis: the block lasts sufficiently long for the procedure but resolves quickly, thus making it possible for the patients to go home earlier. In caesarean section the duration of block is not an issue. On the contrary, the longer the block lasts, the longer is pain free period. As the result the requirements for analgesia is reduced and the patient ends up receiving less opioid after surgery, with all characteristic side-effects of these drugs: nausea and vomiting, constipation, pruritis and so on. The speed of onset is not a factor either, and other local anesthetics are fast enough for moderately urgent cesarean. If it is really urgent the patient will be given general anesthesia.

When TNS is suspected it is most important to exclude other possible causes of pain, such as epidural hematoma, epidural abscess and the damage of the neural structures.

The treatment of TNS is symptomatic. Painkillers are prescribed for controlling the pain, from non-steroidal anti-inflammatory drugs to opioids in severe cases. As mentioned earlier, TNS fully resolves in the majority of patients after 24 hours and does not leave long-term problems. In rare cases however the pain may persist and last up to five days and in very rare cases even longer. In these cases other medications may be used.

To summarize this chapter, the Transient Neurologic Syndrome is characterized by pain in the lower limbs and lower back after spinal anesthetic. The symptoms appear within 24 hours after the block and resolve within a day or two. There is no impairment of either sensation or motor function on examination. Unlike some other complications, it does not lead to permanent damage of neural structures. It is considerably more common when lignocaine is used for the spinal and also when the patients are placed in the lithotomy position. Pregnant patients seem to have lower chance of developing TNS, though further research is needed to confirm this finding.

References:

1. Schneider M, Ettlin T, Kaufmann M, Schumacher P, Urwyler A, Hampl K, Von Hochstetter A. Transient Neurologic Toxicity After Hyperbaric Subarachnoid Anesthesia with 5% Lidocaine. Anesth Analg 1993;76:1154-7.

2. JE Pollock. Transient neurologic symptoms: Etiology, risk factors, and management. Regional Anesthesia and Pain Medicine; Nov/Dec 2002; 27, 6.

3. Aouad MT, Siddik SS, Jalbout MI, Baraka AS. Does Pregnancy Protect Against Intrathecal Lidocaine-Induced Transient Neurologic Symptoms?
Anesth Analg 2001;92:401–4.

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Dr. Eugene Smetannikov is a practicing anesthesiologist with the interest in obstetric anesthesia. He is the author of the most comprehensive book on the subject, The Truth About Labor Epidural