Arachnoiditis

Etiology

The etiology of arachnoiditis is unknown. The time between exposure to a possible insult and the development of clinical symptoms is variable. Inconsistent imaging features also complicate the evaluation process. However, risk factors for the evolution of this condition are categorized as either chemical, mechanical, inflammatory, or infectious. These risk factors include the following:

• Chemical
  • Exposures to neurotoxic substances like sulfite-containing preservatives
  • Blood, such as from SAH
  • 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

Arachnoiditis may also arise without any inciting event.

On exposure to an insult, meningeal scar tissue develops and encapsulates the nerve roots, impairs blood circulation, reduces oxygenation and nutrient delivery, and promotes waste product accumulation. Pain and neurological deficits result from these changes.

Previous trauma, spinal surgery, and SAH are among the most frequently reported causes of arachnoiditis. Chemical exposure may be intentional or unintentional.[7][8][9][10]

Epidemiology

Information about the epidemiology of arachnoiditis is limited. Since Horsley described the condition in 1909 as a disease entity, fewer than 1000 case reports exist in the literature. The true incidence or frequency of arachnoiditis is hard to determine due to its rarity, the diagnostic challenges it brings, and the variety of terms used in the literature to refer to this condition, including “chronic spinal meningitis” and “meningitis serosa circumscripta spinalis.” Arachnoiditis may be subclinical in some patients. Thus, the condition is likely underdiagnosed and underreported. However, the frequency of lumbar arachnoiditis has been recently observed to increase due to the increasing need for lumbar spine surgeries.

Pathophysiology

Exposure to an insult causes inflammation of the subarachnoid or subdural space, precipitating collagen deposits and fibrosis. Scar tissue forms, reducing CSF flow and impairing circulation, toxic metabolite clearance, oxygenation, and nutrient delivery to the neurons. Fibrosis leads to nerve root encapsulation, compression, damage, and atrophy. Arachnoiditis frequently results in pain and may be associated with neurological deficits.[11]

History and Physical

The clinical presentation of arachnoiditis varies widely. History may reveal a slow evolution of back and leg pain with associated multifocal sensory, motor, or reflex deficits. The severity of symptoms ranges from mild to severe and disabling, and the disease course may be static or progressive. The putative cause may be hard to identify, as the time frame from exposure to the onset of symptoms is inconsistent. For example, spinal adhesive arachnoiditis may be reported up to 10 months after an aneurysmal rupture.

Clinical symptoms vary according to the spine levels and severity of the arachnoiditis. Lumbar and thoracic involvement are the most common, followed by lumbosacral disease. Involvement of the entire spine is rare. As for severity, symptoms of severe arachnoiditis include disabling back pain, numbness, paresthesias, myeloradiculopathy symptoms of the lower limb, bowel or bladder dysfunction, sexual dysfunction, difficulty sitting for long periods, and motor weakness.[12]

The most common symptoms of arachnoiditis include back pain, radicular pain, and sensory defects. Motor weakness, gait imbalance, and neurogenic bowel or bladder are less frequent. Urinary symptoms develop late in 23% of arachnoiditis patients and are often characterized by urgency, increased frequency, and less commonly, incontinence. Paraplegia and isolated low-back pain have also been documented.

The neurologic symptoms vary in location and severity. A complete neurologic examination must be performed for all patients suspected of arachnoiditis to guide diagnosis and management.

Evaluation

Arachnoiditis is a clinical diagnosis. Laboratory tests and neurophysiologic modalities like electromyography and nerve conduction studies yield inconsistent results and are not used to formally diagnose the condition.[13][14]

Magnetic resonance imaging (MRI) and computed tomography (CT) myelography have high sensitivity, specificity, and accuracy for chronic adhesive arachnoiditis and may be used to support the clinical findings. However, radiologic features do not always correspond to clinical findings and their severity. Direct visualization by thecaloscopy can help detect loculated arachnoid cysts if MRI results are inconclusive. A spinal cord biopsy is sometimes indicated to exclude the presence of tumors when cord swelling and an intramedullary increased signal are present.[15]

The most frequent MRI findings are loculated arachnoid cysts involving several vertebral bodies or possibly the entire spine. Other common MRI findings include spinal cord swelling with or without increased T2 signal, cord displacement, cord atrophy, nerve root clumping, syrinx formation, and arachnoid septations. Meanwhile, the typical CT myelography findings are myelography spread block, thickened or tethered nerve roots, soft tissue mass within the arachnoid space, and intrathecal calcification.

Of the two, MRI is the imaging modality of choice for adhesive arachnoiditis because it can differentiate between benign meningeal calcification from frank arachnoid tissue ossification. However, non-contrast-enhanced CT is more sensitive than MRI for diagnosing arachnoiditis ossificans.

Treatment / Management

Arachnoiditis has no definitive cure and is often challenging to treat. The management is primarily supportive, focusing mainly on alleviating the symptoms and improving the patient's quality of life. Pain can cause functional limitations. Thus, multimodal and interprofessional pain management strategies are recommended. Medical management may include nonsteroidal anti-inflammatory drugs and opioids. Adjuncts like duloxetine, gabapentin, and pregabalin and muscle relaxants like baclofen may be combined with analgesics.[16]

Physical therapy and psychological strategies like cognitive behavioral therapy, biofeedback, and imagery can modulate a patient's pain perception and help improve symptoms. Individuals who experience difficulty sitting due to pain may benefit significantly from motorized assistive devices like standing wheelchairs. These devices can help improve mobility and quality of life. However, standing acceptance and vibration endurance should be evaluated before proceeding.

Thecaloscopy with dissection of cysts and adhesions and pain-modulating neurostimulation can help alleviate the symptoms, though arachnoiditis can recur afterward. Intrathecal therapy has also been used, though it can worsen the condition.

Surgery's role remains unclear. However, surgery can release a tethered cord and restore CSF flow. Reported surgical interventions include shunting, cyst fenestration, myelotomy, duraplasty, adhesiolysis, and laminectomy.

However, the long-term prognosis after surgery is poor. Surgery can produce immediate improvement, often followed by relapse and progressively worsening symptoms. Decompressive resection of isolated ossified plaques in arachnoiditis ossificans can provide temporary relief, but the condition's outcome remains poor. Various treatment options can restore CSF flow in advanced chronic adhesive arachnoiditis with CSF flow obstruction. However, these interventions do not prevent recurrence.

Preventing arachnoiditis by treating an epidural infection early may be the only case where early surgical intervention is beneficial. Local reduction of the infection can prevent inflammation from passing through the dural sac and causing severe adhesive arachnoiditis.

Improvement after epidural steroid injections has been reported. However, this modality is generally not recommended, as chemical spinal injections can exacerbate the condition. Oral corticosteroids have not shown any therapeutic benefit.

Differential Diagnosis

The differential diagnosis of arachnoiditis includes various conditions affecting the spinal cord, including 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 course of arachnoiditis is highly variable, as this condition can be stable for some individuals but progressive for others. Most patients with arachnoiditis have a relatively stable functional disability with neither significant symptom exacerbation nor improvement from the time of diagnosis. However, symptom severity can fluctuate.

Some individuals may experience a progressive course, developing significant pain, disability, and poor quality of life in the advanced stages. Surgery often does not help and can even aggravate the condition.

Arachnoiditis may cause permanent disability, though the condition itself is usually not life-threatening. Still, the manifestations of severe arachnoiditis can be psychologically detrimental to affected patients. A long-term follow-up study of 50 individuals with arachnoiditis revealed death by suicide in 2 patients and death from causes not directly related to arachnoiditis. The condition tends to shorten patients' life span by an average of 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 this condition's manifestations and improve patient outcomes.