Arachnoiditis After Neuraxial Anaesthesia

Arachnoiditis after neuraxial anaesthesia is chronic inflammation of the arachnoid with fibrosis and adhesion of nerve roots, causing chronic pain and neurological deficit. It is a rare but severe complication.

Epidemiology. Rare; the incidence is unknown. Causes include contaminated or wrong substance injection (chlorhexidine, detergent, contrast, ionic agents), blood in the subarachnoid space, infection, intrathecal steroid, repeated surgery and myelography with oil based dye.

Risk factors. Disinfectant contamination of equipment, injection of a wrong agent, repeated punctures with bleeding, preservative containing solutions, previous spinal surgery and intrathecal steroid.

Pathophysiology.

Meningeal injury triggers inflammation and collagen deposition. Adhesions clump nerve roots (clumped roots, empty thecal sac sign, or a mass in the sac) and reduce blood flow, causing chronic neuropathic pain and weakness.

Burning pain in the back and legs, paraesthesia, bilateral leg weakness, sensory loss, bladder and bowel dysfunction, sexual dysfunction, headache, and spasms. It starts within days to weeks (sometimes months) after the block and is often progressive.

Red flags.

• Progressive weakness.
• Sphincter dysfunction.
• Fever or meningism.

MRI of the lumbar spine with contrast shows clumped nerve roots, an empty thecal sac, or a soft tissue mass in the sac. Cerebrospinal fluid may show raised protein. Nerve conduction and electromyography show multi-root disease. Exclude infection, tumour and haematoma.

Differential diagnosis.

• Failed back syndrome.
• Cauda equina syndrome.
• Infective meningitis.
• Epidural haematoma or abscess.
• Spinal stenosis.
• Tumour.
• Multiple sclerosis.

No disease modifying treatment exists. Care is symptomatic and multidisciplinary.

• Gabapentin: 300 mg orally on day 1, increased every 3 days to 900 to 1,800 mg daily in three divided doses; maximum 3.6 g daily; monitor sedation and renal function; reduce in creatinine clearance under 60 mL/min.
• Pregabalin: 75 mg orally twice daily, increased after 1 week to 150 mg twice daily; maximum 600 mg daily; monitor sedation and weight; halve in creatinine clearance 30 to 60 mL/min.
• Amitriptyline: 10 mg orally at night, increased to 75 mg; maximum 150 mg daily; monitor ECG and anticholinergic effects; avoid in recent myocardial infarction and arrhythmia.
• Duloxetine: 30 mg orally once daily for 1 week, then 60 mg; maximum 120 mg daily; monitor blood pressure and sodium; avoid in severe hepatic or renal impairment (creatinine clearance under 30 mL/min).

Add physiotherapy, psychology, transcutaneous nerve stimulation and, in selected cases, spinal cord stimulation. Steroid injections and surgery do not help and risk worsening.

Prevention. Keep antiseptic solutions away from needles and drugs (let chlorhexidine dry and use sterile technique), check labels, and avoid contaminated trays.

Monitoring. Pain score, neurological examination and function at each review.

Referral and escalation. Neurology and pain service. Disclosure and reporting.