Arachnoiditis

Etiology

The etiology of arachnoiditis is unknown. The interval between exposure to a potential insult and the onset of clinical manifestations is variable. Inconsistent imaging findings further complicate evaluation. Risk factors associated with the development of arachnoiditis are classified as chemical, mechanical, inflammatory, or infectious in origin, as follows:

• Chemical
  • Exposure to neurotoxic substances, such as sulfite-containing preservatives
  • Blood, such as from SAH [3]
  • Direct local anesthetic toxicity
  • Contrast myelography
  • Spinal anesthetic agents
  • Accidental chemical injection
• Mechanical
  • Trauma
  • Surgical meningeal manipulation
  • Spinal surgery
  • Disk herniation
• Inflammatory
  • Ankylosing spondylitis
  • Guillain-Barré syndrome
  • Autoimmune vasculitis
•  Infectious
  • Syphilis
  • Tuberculosis
  • HIV
  • Viral infection
  • Candida and other fungi [4]

Meningeal scar tissue develops following exposure to an insult, encasing the nerve roots, impairing blood flow, reducing oxygen and nutrient delivery, and promoting the accumulation of metabolic waste. These processes result in pain and neurological dysfunction.

Previous trauma, spinal surgery, and SAH are among the most frequently reported causes of arachnoiditis. Chemical exposure may be intentional or unintentional.[5][6][7][8] Arachnoiditis may also arise without a preceding inciting event.

Epidemiology

The condition has been more extensively studied and recognized since its first description by Horsley in 1909. The incidence of lumbar arachnoiditis has increased in recent years, paralleling the growing number of lumbar spine surgeries and improved awareness and diagnostic techniques. Arachnoiditis may present subclinically in some patients and is, therefore, likely underdiagnosed and underreported.

Recent estimates indicate that about 25,000 new cases of arachnoiditis occur globally each year, mainly concentrated in North and South America, Europe, and Asia, corresponding to higher rates of spinal operative procedures in these areas. (Source: Orphanet, 2010) The true incidence is difficult to ascertain because of the condition’s rarity, diagnostic complexity, and the inconsistent terminology used in reports, including "chronic spinal meningitis" and "meningitis serosa circumscripta spinalis."

Pathophysiology

Exposure to an insult induces inflammation within the subarachnoid or subdural spaces, leading to collagen deposition and subsequent fibrosis. Scar formation reduces CSF flow and disrupts circulation, clearance of metabolic byproducts, oxygenation, and nutrient delivery to neural tissues. Progressive fibrosis results in nerve root encasement, compression, injury, and atrophy. Arachnoiditis frequently manifests with pain and may be accompanied by neurological deficits.[9]

History and Physical

The clinical presentation of arachnoiditis is highly variable. The clinical history often reveals a gradual progression from back and leg pain to multifocal sensory, motor, or reflex deficits. Symptom severity ranges from mild to disabling, and the disease course may remain static or progress over time. Identifying the precipitating cause is often difficult because the interval between exposure and symptom onset is inconsistent. For example, spinal adhesive arachnoiditis has been reported up to 10 months after aneurysmal rupture with SAH.

Clinical manifestations depend on the spinal levels affected and the extent of inflammation. Lumbar and thoracic levels are most frequently involved, followed by lumbosacral disease. Panspinal involvement is uncommon. Severe arachnoiditis produces disabling back pain, numbness, paresthesias, myeloradiculopathy of the lower extremities, bowel or bladder dysfunction, sexual dysfunction, difficulty sitting for extended periods, and motor weakness.[10]

The most frequent symptoms include back pain, radicular pain, and sensory disturbances. Motor weakness, gait imbalance, and neurogenic bowel or bladder occur less commonly. Urinary symptoms develop late in approximately 23% of patients and often include urgency, frequency, or, less commonly, incontinence. Paraplegia and isolated low back pain have also been described.

Neurological manifestations vary with disease severity and site of involvement. A complete neurological examination should be performed in all patients with suspected arachnoiditis to guide diagnostic evaluation and management.

Evaluation

Arachnoiditis is a clinical diagnosis. Laboratory testing and neurophysiologic studies, including electromyography and nerve conduction studies, provide inconsistent results and are seldom used to establish the diagnosis.[11][12]

Magnetic resonance imaging (MRI) and computed tomography (CT) myelography demonstrate high sensitivity, specificity, and accuracy for identifying chronic adhesive arachnoiditis and are valuable in supporting clinical findings.[13] However, radiologic abnormalities do not consistently correlate with clinical presentation or disease severity. Direct visualization by thecaloscopy may reveal loculated arachnoid cysts when MRI findings are inconclusive.[14] Spinal cord biopsy is occasionally indicated to exclude neoplasia when MRI demonstrates cord swelling or an intramedullary increased signal.[15]

Typical MRI findings include loculated arachnoid cysts involving multiple vertebral levels or, in severe cases, the entire spinal axis. Additional features include spinal cord swelling with or without T2 hyperintensity, cord displacement or atrophy, nerve root clumping, syrinx formation, and arachnoid septations. CT myelography commonly demonstrates interrupted intrathecal contrast flow, thickened or tethered nerve roots, intrathecal soft tissue masses, and calcification within the arachnoid space.

Between the 2 modalities, MRI is preferred for evaluating adhesive arachnoiditis because it allows distinction between benign meningeal calcification and true arachnoid ossification. However, noncontrast-enhanced CT is more sensitive than MRI for the detection of arachnoiditis ossificans.

Treatment / Management

Arachnoiditis has no definitive cure and is difficult to manage. Treatment is primarily supportive, directed toward symptom control and improvement of quality of life. Pain often leads to functional impairment. Therefore, multimodal and interprofessional pain management is recommended. Pharmacologic management may include nonsteroidal anti-inflammatory drugs and opioids. Adjunct medications such as duloxetine, gabapentin, pregabalin, and the muscle relaxant baclofen may be used in combination with analgesics.[16]

Physical therapy and psychological interventions, including cognitive behavioral therapy, biofeedback, and guided imagery, can help modulate pain perception and improve overall function. Patients who experience severe sitting intolerance may benefit from motorized assistive devices such as standing wheelchairs, which can enhance mobility and quality of life.

Thecaloscopy with dissection of arachnoid cysts and adhesions, as well as pain-modulating neurostimulation, may provide symptom relief, though recurrence is common. Intrathecal therapy has also been attempted but may, in some cases, exacerbate the condition.

The role of surgery in arachnoiditis is unclear. Surgical intervention can release a tethered cord and restore CSF flow. Reported procedures include shunting, cyst fenestration, myelotomy, duraplasty, adhesiolysis, and laminectomy.

The long-term prognosis after surgery is poor. Surgery may produce immediate improvement but is frequently followed by recurrence and progressive worsening of symptoms. Decompressive resection of isolated ossified plaques in arachnoiditis ossificans can provide temporary relief, but long-term outcomes are unfavorable. Several procedures can restore CSF flow in advanced chronic adhesive arachnoiditis with obstruction, though these interventions do not prevent recurrence.

Preventing arachnoiditis through early treatment of an epidural infection may be the only situation in which early surgical intervention is beneficial. Timely local resolution of infection can prevent inflammation from spreading within the thecal sac and developing into severe adhesive arachnoiditis.

Symptomatic improvement after epidural steroid injections has been reported, but this approach is generally discouraged because chemical spinal injections can aggravate the condition. Oral corticosteroids have not demonstrated therapeutic benefit.

Differential Diagnosis

The differential diagnosis of arachnoiditis includes various conditions affecting the spinal cord, such as the following:

• Spinal cord tumors
• Disk herniations
• Postlaminectomy pain syndrome
• Multiple sclerosis
• Cauda equina syndrome
• Syringomyelia
• Epidural abscess
• Epidural hematoma
• CNS infection [17]

A thorough clinical evaluation supported by imaging findings can help distinguish arachnoiditis from these conditions.

Prognosis

The clinical course of arachnoiditis is highly variable. The condition may remain stable in some individuals but progress in others. Most patients have a relatively consistent level of functional disability, with no substantial symptom exacerbation or improvement following diagnosis, although symptom severity can fluctuate.

A progressive course may occur in some individuals, leading to severe pain, disability, and poor quality of life in advanced stages. Surgical intervention often provides no benefit and may exacerbate the condition.

Arachnoiditis can cause permanent disability, although it is not typically life-threatening. Severe forms may produce significant psychological distress. In a long-term follow-up study of 50 individuals with arachnoiditis, 2 deaths by suicide were reported, with other deaths attributed to unrelated causes. The condition has been associated with an average reduction in life expectancy of approximately 12 years.

Complications

The possible complications of arachnoiditis include the following:

• Chronic pain
• Debilitating neurologic deficits
• Syringomyelia
• Hydrocephalus
• Arachnoid cysts
• Sexual dysfunction
• Loss of bladder and bowel control

Supportive measures, physical therapy, and psychosocial support can help mitigate some of the clinical manifestations of arachnoiditis and improve patient outcomes.