Arachnoiditis is a rare condition comprising chronic radicular pain associated with radiologically diagnosed abnormalities, classically filling defects in the subarachnoid space, absence of spinal nerve root sleeves, arachnoid cysts and obstruction to flow of radioopaque contrast medium. It is important to realise that radiological abnormalities may be present in asymptomatic patients, and a diagnosis of arachnoiditis should not be made on radiological criteria alone. It may occur spontaneously, although it has followed radiation and perispinal injection of irritant substances, such as the oil-based contrast medium that used to be employed for myelography. Antiseptic solutions, powder from surgical gloves and preservatives in drug solutions (e.g. sodium metabisulfite) have been implicated, as have infection and traumatic bleeding. Arachnoiditis has been reported following regional anaesthesia and analgesia, including after epidural blood patch, but it is very rare and the precise aetiology is uncertain (apart from cases following obvious injection of antiseptic solution).
Arachnoiditis may occasionally be confused with cauda equina syndrome; typical features of the two conditions are shown in Table 55.1.
Problems and special considerations
Chronic adhesive arachnoiditis may develop several months or even years after the trigger, so it may be difficult to establish a causal link. Typically, arachnoiditis presents with back pain that worsens with activity, with or without leg pain, paraesthesia or weakness. It is usually steadily progressive and may follow neurological complications of regional anaesthesia.
Table 55.1 Typical features of arachnoiditis and cauda equina syndrome
|
Aetiology |
Features |
|
|
Arachnoiditis |
Inflammation of the arachnoid meningeal layer and subarachnoid space Progressive fibrosis may cause spinal canal narrowing, ischaemia and permanent nerve damage |
Meningeal irritation may occur early, although usually presents months or years later May involve the cauda equina, presenting with similar features Rarely extends cranially |
|
Cauda equina syndrome |
Damage to the lumbosacral nerve roots |
Presents soon after regional anaesthesia, with numbness in corresponding myotomes, sphincter dysfunction |
Management options
Although obstetric regional analgesia and anaesthesia are considered to be extremely safe, it is important to maintain scrupulous attention to aseptic and atraumatic technique and to minimise the use of novel drugs and multiple combinations of drugs. Thus all solutions injected epidurally or spinally should be carefully checked first. Chlorhexidine used for skin asepsis is neurotoxic, and while arachnoiditis has followed accidental injection of large amounts into the neuraxis, introduction of even apparently insignificant traces has been linked (somewhat controversially) with its development. The use of 0.5% chlorhexidine in alcohol is therefore recommended over the 2% solution, and steps to minimise the potential for accidental contamination of equipment or injectate with antiseptic solution should be taken, as per the available guidance.
Once a diagnosis of arachnoiditis is suspected, early involvement of a neurologist is mandatory, with confirmation of the diagnosis by magnetic resonance imaging (MRI) scan. Detailed follow-up and possibly long-term support will be required. There is no specific treatment for arachnoiditis; steroids have been tried, although they are thought to be effective only in the very acute stage of the inflammatory process. Psychological support is important, since the consequences of the condition may be catastrophic.
Key points
• Arachnoiditis is inflammation of the arachnoid and subarachnoid space; it typically occurs months or more after injury.
• Although rare, it may cause permanent neurological damage.
• Meticulous attention must be paid to maintaining aseptic precautions and the avoidance of accidental contamination of regional anaesthetic equipment or drugs with antiseptic solution.
Further reading
Association of Anaesthetists of Great Britain and Ireland, Obstetric Anaesthetists’ Association, Regional Anaesthesia UK. Regional anaesthesia and patients with abnormalities of coagulation. Anaesthesia 2013; 68: 966-72.
Association of Anaesthetists of Great Britain and Ireland, Obstetric Anaesthetists’ Association, Regional Anaesthesia UK, Association of Paediatric Anaesthetists of Great Britain and Ireland. Safety guideline: skin antisepsis for central neuraxial blockade. Anaesthesia 2014; 69: 1279-86.
Carlsward C, Darvish B, Tunelli J, Irestedt L. Chronic adhesive arachnoiditis after repeat epidural blood patch. Int J Obstet Anesth 2015; 24: 280-3.
Moen V, Irestedt L. Neurological complications following central neuraxial blockades in obstetrics. Curr Opin Anaesthesiol 2008; 21: 275-80.