Arachnoiditis: symptoms, causes, diagnosis and treatment

Arachnoiditis is inflammation of the thin membranes that surround the spinal cord and nerve roots. The Acta Neurologica Belgica review describes adhesive arachnoiditis as a rare entity caused by an inflammatory process, and explains that inflammation produces fibrous tissue and adhesions, with nerve roots sticking to each other and to the sac of fluid around the cord (the thecal sac).

The review notes that this membrane has no blood vessels or nerves of its own, which makes healing very difficult, and that the constant circulation of cerebrospinal fluid washes away cells and enzymes that would otherwise help prevent scar tissue forming. Because it is rare, the true number of cases is unknown and may be underestimated.

The review says the symptoms vary significantly between people, from no symptoms at all to severe disability. The sources describe the following possible features.

• Painful radicular syndromes: burning pain in the distribution of the sciatic nerve down the leg, and lower back (lumbago-type) pain.

• Restricted movement in the lower spine.

• Weakness or sensory loss in the area supplied by the affected nerve roots.

• Bladder dysfunction when the spinal cord or its lower nerve roots are involved.

• Leg weakness (paraparesis), which in severe cases can lead to wheelchair use.

The review says the causes are heterogeneous. The most common include infections (bacterial, tuberculous and syphilitic), trauma including the consequences of surgical procedures, contamination of the thecal sac by injections of substances into the spinal canal, such as iodine-based contrast agents and corticosteroids, and spinal canal tumours.

It names iatrogenic damage, meaning harm caused by medical procedures, as an important risk factor, including neurosurgical operations, injections of oil-based contrast agents and epidural anaesthesia. It adds that bleeding during spinal procedures may itself contribute to starting the inflammation. On epidural or spinal anaesthesia, the review states that the link with arachnoiditis seems questionable, and notes that the two largest cohort studies, from the United Kingdom and Finland, did not link them either. Spinal surgery is one of the best recognised causes and is commonly known as failed back surgery syndrome.

The review describes MRI as playing a crucial part in diagnosis, with a reported sensitivity of about 92% and specificity that reaches 100%. The most common MRI abnormalities it lists include arachnoid cysts, and clumping, thickening and displacement of nerve roots, which may light up with contrast, spinal cord swelling, and in later stages shrinkage of the spinal cord with formation of a fluid-filled cavity (syrinx).

Doctors consider the diagnosis when someone has leg weakness or nerve pain together with risk factors such as spinal surgery, spinal anaesthesia, myelography or spinal tumours. The review recommends that this possibility be included in the diagnostic work-up in such cases. The NHS advice for back pain that does not improve is to see a GP, so a first step for persistent leg and back symptoms is a GP assessment and onward referral.

The review is blunt: treatment is extremely difficult, there is no causative treatment, and symptom-based therapy rarely brings the results expected. Opioid and non-opioid painkillers, steroids and spinal cord stimulation are among the most widely used methods. There is no agreement on guideline management, and decisions are made case by case. Surgery to free adhesions remains controversial because its effectiveness has not been confirmed and the disease often recurs or progresses after operation.

Because arachnoiditis typically causes burning, shooting nerve pain, general neuropathic pain guidance applies. NICE CKS says a person with neuropathic pain (other than trigeminal neuralgia or sciatica) should be offered a choice of amitriptyline, duloxetine, gabapentin or pregabalin, with the dose titrated according to response and tolerability. It says all four can be associated with dependence or withdrawal symptoms, so the risks should be discussed. If one is not effective or not tolerated, another of the four is offered. CKS also says non-drug treatments such as physical and psychological therapies, offered through a rehabilitation service, and surgery through specialist services should be discussed.

NICE CKS advises considering referral to specialist pain services at any stage if pain is severe, significantly limits participation in daily activities, or the underlying condition has deteriorated. The NHS back pain page lists CBT to help cope with the pain, group exercise and physiotherapy among treatments for back pain that does not improve.

The NHS says to call 999 or go to A&E if you have back pain and any of the following: pain, tingling, weakness or numbness in both legs, a loss of feeling around your genitals or anus, changes in your bladder or bowels (such as difficulty peeing, or peeing or pooing yourself), changes in how your penis or vagina feels during sex, not being able to get or keep an erection or not being able to orgasm, chest pain, or if the pain started after a serious accident. These can be signs of damage to the nerves at the base of the spine. Do not drive yourself to A&E.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you have back pain and you feel hot, cold, shivery or generally unwell, or the pain is severe, starts suddenly or is getting worse quickly. A new fever and back pain after a spinal procedure should not wait.

Long-term neuropathic pain often persists. NICE CKS says that in many cases it is not possible to cure the underlying disease or reverse the neurological changes, so pain often persists long term, and describes it as typically shooting, stabbing, burning, tingling, numb, prickling or itching. A plan that covers medicines, activity, sleep and mood tends to work better than one that relies on a single treatment.

The NHS suggests staying active and not staying in bed for long periods for back pain generally; discuss with your specialist what activity suits your condition.

On the NHS the first step is a GP, who can refer to a neurologist, spinal surgeon or pain service. NICE CKS lists severe pain, pain limiting daily activities and deterioration as reasons to consider specialist pain referral, and the NHS says you can refer yourself to community musculoskeletal (MSK) services for back or joint help in many areas.

Some people choose a private consultation for faster access to MRI or a second opinion. As this is a rare condition with little guideline agreement, ask for the MRI images and reports to be shared with your NHS team, and ask any specialist how often they see arachnoiditis.