EPIDURAL ANAESTHESIA AND ARACHNOIDITIS
by Sarah Smith

 

The issue of whether epidural anaesthesia is a causative factor in arachnoiditis arouses considerable controversy: this is unsurprising bearing in mind that probably the most common usage is for pain relief during childbirth. This could therefore be an issue of widespread implications.

Epidural and spinal anaesthesia results from the interaction of local anaesthetic agents with nerves, primarily those in the subarachnoid space. Local anaesthetic preparations contain various preservatives, some of which are known to be neurotoxic. Ionic forms are CNS toxic ()

There are a number of documented cases of arachnoiditis secondary to epidural anaesthesia, and indeed, it is recognised as a rare complication of this procedure. However, the true incidence remains unknown, as most studies of the adverse effects of anaesthesia tend to concentrate on the immediate and short-term problems. In addition, studies concerning long-term back pain following epidurals may fail to include cases of neurological damage and arachnoiditis continues to be significantly under-diagnosed.

The following evidence is presented to demonstrate the need to investigate this problem more closely: if nothing else, to exclude arachnoiditis as a significant risk in what is a commonplace procedure.

 

TOXICITY OF LOCAL ANAESTHETICS

Toxicity of local anaesthetics has a direct effect on nervous tissue. This toxicity is determined by various factors such as site of injection, concentration of the agent and whether it is ionic or non-ionic. Also, additives of vasoconstrictive agents, both catecholamine and non-catecholamine may be used.

"All local anesthetic molecules at sufficient concentration are directly cytotoxic to nerve cells"(i)

Powell and Myers () assessed local anaesthetic toxicity on rat sciatic nerves and found that "both nerve injury and edema increased with concentration."

Burm () noted that epidural doses must be much higher than spinal doses, due to the uptake into extraneural tissues and systemic absorption.

Professor Ginther of UC Irvine Medical Centre mentions "peripheral neurotoxicity such as prolonged sensory and motor deficits" in his Internet discussion on toxicity of local anaesthetics. This has been hypothesised as being due to a combination of low pH and the preservatives such as sodium bisulfite in the mixture. Indeed, a recent case of adhesive arachnoiditis following bupivicaine containing preservatives was cited by Uefuji() in Japan.

Malinovsky () discusses the various causes of neurological lesions, including direct trauma of the spinal cord and nerve roots, compromised spinal cord perfusion and direct neurotoxic effect. He suggests that "neurotoxicity can result from decrease in neuronal blood supply, elicited by high concentrations of the solutions, long duration exposure to local anaesthetics, and the use of adjuvants."

He advocates several measures to reduce the incidence of neurotoxicity: use of the lowest efficient dose, avoidance of repeated or large volume injections and use of preservative-free solutions. As early as 1954, Moore () advised that local anaesthetic administered epidurally should be free of preservatives.

 

PREVIOUS SPINAL PROBLEMS

A further important point is that in patients with pre-existing spinal problems ( including spina bifida occulta or arteriovenous malformation of which they may be unaware), the risk of problems may be higher. McGrady and Davis() raised this point in their 1988 paper, stating a 5-10% incidence of spina bifida occulta(SBO) in the general population and they contended that "Attempted epidural puncture at the level of the lesion will almost certainly result in a dural tap." They describe a case of complications due to epidural anaesthesia in SBO and also raised the issue that cases like this had not been previously published, "although it is unlikely to be an isolated case."

If the epidural space is already compromised by disc herniation, stenosis or epidural fibrosis, the risk is greater. Yuen et al () state that neurological complications " may be more severe in the presence of spinal stenosis".

Butler and Fuller in their 1998 study() concluded that "A previous history of back pain increases the likelihood of post-partum back pain following epidural anaesthesia".

Rocco et al () in a study of pressure gradients in the epidural space, concluded that as resistance to inflow of fluid was significantly higher in the diseased epidural space, "spread of anesthetics might be difficult to predict".

 

DURAL PUNCTURE

The commonest neurological complication of epidural anaesthesia is dural puncture.

One of the problems with dural puncture is that blood (which is known to be highly irritant) may enter the subarachnoid space. Indeed, a blood patch is often applied to prevent loss of spinal fluid through the breached dural membrane, so that blood products are introduced into the area.

In 1996, Costigan and Sprigge() published a study of dural puncture cases. They concluded that :"Headache and backache are both common following dural puncture with a 16 G needle and both frequently recur after discharge from hospital. It was the strongly expressed opinion of this selected group* that all mothers should be warned of the risk of dural puncture before undergoing epidural analgesia." (* i.e. the patients in the study)

MacArthur et al published a study() of long-term headache following dural puncture and found that of 74 women who had suffered an accidental dural puncture during epidural anaesthetic, 10 had persistent headache after several years. They concluded that "the findings provide a clear indication of the need for further study of the possible long term sequelae of accidental dural puncture." It should be noted that the authors only looked at head and neck pain, not lumbar , thoracic or limb pain.

Blood in the subarachnoid space is a known causative factor of arachnoiditis.

Combined spinal epidural anaesthetic (CSE) is a technique that sets out to deliberately produce a multicompartment block through a breached dural membrane. This means that potentially there may be a leak of an epidural bolus into the subarachnoid space.()

 

NEUROLOGICAL COMPLICATIONS OF EPIDURAL ANAESTHESIA

Dr. Muir of Dalhousie University in Canada, mentions the following in her review(): "neurologic problems ranging from headache to paralysis" and she includes adhesive arachnoiditis in her list.

 

SHORT-TERM COMPLICATIONS: ()

Post dural puncture headache (commonest)

Total spinal anaesthesia

Meningitis (infective or chemical)

Extradural haematoma

Extradural abscess

Anterior spinal artery syndrome (paraplegia)

Intravascular injection

Cauda equina syndrome(CES)

Transient radicular irritation(TRI)

Cranial nerve lesions/Horner s syndrome (v. rare)

Hampl et al() suggested that transient neurologic symptoms are "common after spinal anesthesia" and may occur in up to "one third of the patients receiving 5% lidocaine."

Dahlgren () wrote about Transient Radicular Irritation(TRI) having an incidence of 15-37% in those patients receiving lidocaine, procaine and mepivicaine (but not bupivicaine). He ascribes the symptoms to hemolyzed blood in the subarachnoid space.

 

BACK PAIN FOLLOWING EPIDURAL ANAESTHESIA

MacArthur et al() in 1990 did a study of over 1000 women who suffered from back pain after childbirth (nearly 70% of whom had had it for over 1 year). They concluded that "The relation between backache and epidural anaesthesia is probably causal. It seems to result from a combination of effective analgesia and stressed posture during labour. Further investigations on the mechanisms causing backache after epidural anaesthesia are required."

Their 1992 paper() discussed 26 women who had numbness or tingling in the lower back, buttocks and leg, of whom 23 had had epidural anaesthesia. Again, they concluded that further study was needed. They went on to do studies in 1995 (short-term)() and 1997 (long-term)() but these failed to show significant increase in back pain amongst women who had had epidural anaesthesia.

Other studies have also failed to demonstrate a significant correlation between epidural anaesthesia and long-term back pain. Russell et al s study () showed 33% of participants suffering from back pain at 3 months post-partum, but only 7% of these had not previously suffered from back pain. There was further follow-up at one year, but these results are unclear. They concluded that "Among all demographic, obstetric, and epidural variables examined the only factors significantly associated with backache after childbirth were backache before and during pregnancy." In a previous study(), Russell had contended that "Though new long term backache is reported more commonly after epidural analgesia in labour, it tends to be postural and not severe. There were no differences in the nature of the backache between those who had or had not received epidural analgesia in labour."

 

LONG-TERM NEUROLOGICAL COMPLICATIONS

A Swedish study() of peripheral neurologic deficits found that there might be a correlation with higher concentrations of lidocaine, but their database was incomplete and therefore no conclusive statement could be made. They noted bladder, bowel and sexual dysfunction and motor deficits as well as lumbar and limb pain.

 

ARACHNOIDITIS CASES

Palot et al () include arachnoiditis as a cause of prolonged neurological complications of obstetrical epidural analgesia, but concluded that long-term problems are rare.

Sghirlanzoni et al () discuss six patients with arachnoiditis secondary to epidural anaesthesia (no other risk factors were involved). Of these, only two patients had also had transient distress immediately following the procedure, and all the procedures had apparently been performed in a standard manner without obvious complication at the time.

Vandermeulen () includes arachnoiditis as a "mishap"& "solely due to & epidural anaesthesia". Haisa et al () state that lumbar adhesive arachnoiditis should be considered for differential diagnosis of back and leg pain after epidural anaesthesia. They discuss the case of a 30 year old patient who developed arachnoiditis after epidural intubation for anaesthesia during childbirth.

Furthermore, epidural anaesthesia may cause subarachnoid cysts or cavities, which are also recognised complications of arachnoiditis.

Torres et al() suggested that "meningeal inflammation may have left scars which later induced ischemia and subsequent cavitation." Alternatively, CSF flow may have been impeded, thus dilating the central canal and causing compressive ischaemia, thence myelomalacia and cavitation. They discussed seven patients with spinal arachnoiditis secondary to epidural anaesthesia, all of whom had subarachnoid cysts and five had cord cavitation.

Sklar et al() noted subarachnoid cysts on MR scan, with irregularity of the surface of the cord, intramedullary cysts and myelomalacia, in patients following epidural anaesthesia. However, in four cases, arachnoiditis was not suspected clinically.

Other authors() have also discussed arachnoid cysts secondary to epidural anesthesia.

 

CONCLUSIONS:

Breivik()commented that "A number of well documented cases have been published in which surgery or patient-related pathology were primary causes of "typical" spinal or epidural neurological complications. These emphasize the importance of searching for other risk factors of neurological sequelae after surgery or child birth in cases where there is no obvious deviation from the normal epidural or spinal procedures"

Durbridge and Holdcroft() at the Hammersmith Hospital stated that "prospective studies have not confirmed any causal relationship between epidural analgesia and backache and neurological complications are five times more common after childbirth itself than after regional nerve blockade. Postpartum symptomatology describes significant morbidity in the community but its relationship to analgesia in labour is still to be proved." This is an important point: childbirth itself can cause problems, so we would need to establish to what degree this is a significant causative factor in cases of arachnoiditis. History of complications during labour (e.g. forceps delivery) must be taken into account. However, MacArthur s 1990 study () did not find any difference between "normal" and "abnormal" deliveries. This obviously needs to be investigated further.

The majority of medical literature does appear to suggest that epidural anaesthesia is not a significant cause of chronic back pain in young mothers.

However, one must bear in mind that some studies will not have looked at neurological aspects or will have concentrated on problems within the first year following childbirth and it may be that more long-term studies are needed to establish the incidence of arachnoiditis.

Also, it is vital to remember that ALL medical treatment carries some risk and what must be borne in mind is the BENEFIT:RISK RATIO. In the case of a healthy mother with a normal labour and a healthy baby, epidural anaesthesia does carry a relatively low benefit: risk ratio: other pain relief can be used successfully with less risk. On the other hand, in a more complex clinical situation, say pre-eclampsia or other maternal morbidity, epidural anaesthesia may confer less maternal risk than general anaesthesia. Similarly, foetal morbidity risks must be taken into account.

It is important to put the above information into context, but unfortunately, there is insufficient data to allow this, as the true incidence of arachnoiditis remains unknown.(adverse drug reactions are under-reported).

What is probable is that those who have pre-existing spinal problems (whether recognised or not) are likely to have a higher risk of adverse events following epidural or spinal anaesthesia.

In the meantime, until further research is carried out, it would seem advisable to counsel caution with these procedures in patients who have back problems .

Arachnoiditis is a recognised complication of epidural anaesthesia and this should be mentioned as a risk (albeit probably rare) in obtaining informed consent to this invasive procedure.

A final point: those patients who have persistent back pain with or without discernible neurological deficit, following epidural anaesthesia, should be fully investigated to exclude arachnoiditis, which of course, is as yet an incurable and devastating condition .

 

Sarah Andreae-Jones MB BS, Patron of the Arachnoiditis Trust , November 1999.

 

 

 

References:

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Yuen EC, Layzer RB, Weitz SR, Olney RK Neurology 1995 Oct; 45(10): 1795-801 Neurological complications of lumbar epidural anesthesia and analgesia.

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Rocco AG, Philip JH, Boas RA, Scott D Reg Anesth 1997 Mar-Apr; 22(2):167-77 Epidural space as a Starling resistor and elevation of inflow resistance in a diseased epidural space.

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Muir HA Department of Anaesthesia, Dalhousie University, Nova Scotia, Canada, " Epidural Misadventures; A review of the risk and complications."

With reference to: University of Queensland Internet site "Neurological Complications of epidurals"

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