Arachnoiditis
Chronic inflammation and scarring of the spinal nerve root lining
ICD-10: G03.9 · systemic condition
Arachnoiditis is a painful condition caused by inflammation of the arachnoid mater — the middle layer of the three membranes (meninges) surrounding the spinal cord and nerve roots. When the arachnoid membrane becomes inflamed, it can develop scar tissue that binds nerve roots together, tethers them to the dural sac, or restricts their normal gliding movement. The result is often severe, chronic, and refractory pain that is difficult to treat. Arachnoiditis is most commonly caused by prior spinal surgery, epidural steroid injections, spinal infections, or by contrast agents used in older myelography procedures (oil-based myelographic dye was a leading historical cause). It is a distinct entity from the much more common post-surgical pain syndromes, and it is frequently underdiagnosed.
50%
Spinal cord stimulation achieves clinically meaningful pain reduction (≥50%) in approximately 50–60% of carefully selected patients with arachnoiditis.
North American Spine Society,
Prior spinal surgery is now the most common identifiable cause of arachnoiditis, accounting for the majority of current cases since oil-based myelographic contrast was discontinued in the 1980s.
Aldrete JA et al., Pain Practice (2006)Symptoms
- Burning, stinging, or stabbing pain in the lower back, legs, or perineum — often severe
- Leg weakness and sensory changes — numbness, tingling, or hypersensitivity
- Muscle cramps and spasms, particularly in the legs
- Bowel and bladder dysfunction
- Shooting or electric shock-like pains (dysesthesias)
- Symptoms that are variable — worsened by movement, weather changes, or stress
- Neurological deficits — in severe cases, progressive lower extremity weakness
Causes & Risk Factors
- Prior spinal surgery — the most common current cause; inflammation during healing can scar nerve roots
- Multiple epidural steroid injections at the same level — especially when performed without image guidance
- Spinal infection (meningitis, discitis, or epidural abscess) causing reactive scarring
- Oil-based myelography contrast (Pantopaque) — the leading cause prior to the 1980s; now discontinued
- Intrathecal medications (especially when preservatives are present)
- Spinal cord or cauda equina trauma
Imaging Findings
Imaging studies are commonly used to identify findings associated with this condition. Results vary by individual; a qualified spine specialist interprets findings in the context of a full clinical evaluation.
MRI
- "Clumped" nerve roots — roots adhered together into one or several bundles in the thecal sac
- "Empty sac" sign — roots adherent to dural walls with a featureless fluid space centrally
- "Soft tissue mass" pattern — roots conglomerated into a single central mass (most severe)
- No contrast enhancement in chronic arachnoiditis; active/infectious arachnoiditis may enhance
- Note: MRI is the definitive imaging modality; myelography (which can worsen arachnoiditis) is rarely used
CT Scan
- Thecal sac irregularity and nerve root clumping on CT myelogram (historically used before MRI)
- Calcification within the arachnoid membrane in chronic or ossifying arachnoiditis
- Syringomyelia (fluid cavity within the cord) as a complication in severe cases
X-Ray
- Not useful for diagnosis; may show prior surgery hardware, disc space narrowing, or evidence of prior infection
- Calcification of the arachnoid (arachnoiditis ossificans) may rarely be visible on plain films
Who Is Commonly Affected
The following patterns are commonly associated with this condition based on published population studies. Individual presentation varies; these figures are informational only.
Peak Age Range
40–65 years (typically presenting years after the inciting event)
Gender Distribution
Roughly equal; some series show slight female predominance in post-surgical cases
Estimated Prevalence
Exact prevalence unknown; historically associated with oil-based intrathecal contrast agents (largely eliminated); now most common after repeated lumbar surgery
Treatment Options
Conservative
- Multimodal pain management — gabapentin/pregabalin, tricyclic antidepressants, opioids in carefully selected cases
- Physical therapy — hydrotherapy and gentle movement to maintain function
- Spinal cord stimulation (SCS) — the most evidence-supported interventional treatment for refractory arachnoiditis
- Intrathecal drug delivery (pain pump) for severe, opioid-responsive cases
- Psychological support and pain psychology — essential given the chronic, refractory nature
Surgical
- Surgical lysis of adhesions (adhesiolysis) — technically complex, outcomes variable, risk of worsening
- Spinal cord stimulator implantation — typically classified as interventional rather than "surgical" but requires implantation
When to see a spine specialist
If you have had prior spinal surgery or epidural injections and experience progressive burning leg pain, new neurological deficits, or bowel/bladder dysfunction, see a spine specialist promptly. Arachnoiditis is best evaluated by an experienced spine specialist or pain management physician who can order and interpret MRI with appropriate protocols and rule out other treatable causes of post-procedural pain.
Specialists Who Treat Arachnoiditis
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Questions to Ask Your Doctor
Bring these questions to your next appointment about arachnoiditis.
- 1
What do you think caused my arachnoiditis — prior surgery, infection, contrast dye, or something else?
- 2
What does my MRI show — are the nerve roots clumped, adhered to the dural sac wall, or forming a central mass?
- 3
What pain management approaches have the best evidence for arachnoiditis specifically?
- 4
Is spinal cord stimulation a realistic option for my level of pain, and who should I consult?
- 5
Are there any experimental or emerging treatments I should be aware of?
Research Evidence
No studies reviewed yet for this condition. Check back soon — our evidence pipeline runs nightly.
Clinical Evidence
Frequently Asked Questions
How is arachnoiditis diagnosed?
MRI of the lumbar spine with and without contrast is the primary diagnostic tool. Characteristic findings include clumping of nerve roots into a central mass ("empty sac" sign), adhesion of nerve roots to the dural sac peripherally ("pseudocord" sign), or a completely obliterated thecal sac filled with fibrous tissue. These MRI patterns are graded (Type I, II, III) and correlate with symptom severity. Diagnosis requires both the clinical picture and consistent MRI findings.
Is arachnoiditis curable?
Currently there is no cure for arachnoiditis. Once scar tissue has formed around the spinal nerve roots, it cannot be reliably removed without risk of causing further nerve damage. Treatment focuses on pain control and preserving function. Spinal cord stimulation is the most effective long-term intervention, with studies showing 50–60% of patients achieving meaningful pain reduction. The condition does not inevitably worsen — many patients reach a plateau and achieve stable management.
What is the relationship between epidural steroid injections and arachnoiditis?
Single, properly performed, image-guided epidural steroid injections have an extremely low risk of causing arachnoiditis. The risk increases with multiple injections at the same level, injections performed without fluoroscopic or CT guidance (increasing the risk of inadvertent intrathecal injection of particulate steroid), and the use of methylprednisolone acetate (Depo-Medrol) intrathecally, which has documented neurotoxicity. The FDA cautions against epidural injection of particulate corticosteroids. The absolute risk remains very low, but it is a known possible complication.