Arachnoiditis

Arachnoiditis is a painful inflammatory condition affecting the arachnoid — the middle of the three membranes (meninges) that surround and protect the spinal cord and nerve roots. Chronic inflammation causes the arachnoid to become scarred and thickened, leading to adhesion of nerve roots and a variety of debilitating neurological symptoms.

Arachnoiditis is one of the most serious long-term complications of spinal pathology and intervention. It is a recognized consequence of Spinal Infection and Failed Back Surgery Syndrome, where repeated procedures and epidural scarring drive chronic nerve root adhesion. It is also an important cause of Syringomyelia and Tethered Cord Syndrome when scarring restricts normal cerebrospinal fluid flow and cord mobility.

Causes

Spinal procedures and injections.

Arachnoiditis can be triggered by various spinal interventions, including myelography with older oil-based contrast agents (now discontinued), spinal surgeries, epidural steroid injections, and lumbar punctures — particularly when complicated by bleeding or infection. Repeated spinal procedures increase the cumulative risk.

Other causes

Bacterial or viral meningitis and spinal infections can cause arachnoiditis through direct inflammatory damage to the arachnoid membrane. Spinal cord injury, chronic compression from disc disease or spinal stenosis, and rarely, intrathecal chemotherapy have also been implicated. In some cases no precipitating cause is found.

Symptoms

Arachnoiditis produces a variable and often severe symptom picture. The most common complaint is chronic, burning pain in the lower back and legs. Patients may also experience abnormal sensations such as tingling, numbness, or a sensation of insects crawling on the skin (formication). Muscle cramps, spasms, and weakness in the lower extremities are common, as are bladder, bowel, and sexual dysfunction. Symptoms are typically constant and do not follow a predictable radicular pattern, which can make diagnosis challenging.

Diagnosis

MRI with contrast is the most useful imaging tool, showing characteristic clumping, adhesion, and displacement of nerve roots within the thecal sac. A lumbar spine MRI is most commonly obtained as the lumbar region is most frequently affected, though a cervical spine MRI may be needed when upper cord involvement is suspected. Three classic patterns are recognized on MRI: central clumping of nerve roots, peripheral adhesion of roots to the dural sac walls (the "empty sac" appearance), and inflammatory soft tissue mass replacing the normal nerve root pattern. CT myelography — though itself a potential irritant to the arachnoid — may be used in selected cases and demonstrates irregular filling defects and nerve root adhesions.

MRI Pattern Classification

Arachnoiditis is classified by its MRI appearance, which corresponds to progressive stages of nerve root adhesion and scarring.

• Type I: Central conglomeration — nerve roots clump together centrally within the thecal sac.
• Type II: Peripheral adhesion — nerve roots adhere to the dural walls, creating the "empty sac" appearance.
• Type III: Inflammatory mass — complete replacement of the subarachnoid space by soft tissue with loss of individual root identification.

Treatments

There is currently no cure for arachnoiditis, and treatment focuses on managing chronic pain and maximizing functional quality of life. Because scar tissue cannot be safely removed without risking further nerve damage, the therapeutic approach is largely supportive and multidisciplinary.

A comprehensive pain management program involving specialists in neurology, pain medicine, and rehabilitation is the foundation of care for most patients with arachnoiditis.

Pain management: Neuropathic pain medications such as gabapentin, pregabalin, duloxetine, and tricyclic antidepressants can help manage burning and dysesthetic pain. Opioid analgesics may be considered for refractory pain under careful supervision. Intrathecal drug delivery systems (pain pumps) can provide effective pain control with lower systemic side effects in carefully selected patients.

Rehabilitation and interventional options

Physical therapy focused on gentle mobility, core stabilization, and hydrotherapy can help manage symptoms and prevent deconditioning. Spinal cord stimulation — delivering low-level electrical impulses to the spinal cord through implanted electrodes — has shown benefit in some patients with refractory arachnoiditis pain. Psychological support and pain coping strategies are important components of long-term management given the chronic nature of this condition.

Related Spine Conditions

• Failed Back Surgery Syndrome
• Osteomyelitis and Spinal Abscess
• Syringomyelia
• Tethered Cord Syndrome
• Transverse Myelitis
• Back to all Spine Conditions