What Is Arachnoiditis?

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Arachnoiditis is a rare, painful condition characterized by inflammation of the arachnoid mater, one of the membranes covering the spinal cord, brain, and nerve roots. Since the arachnoid helps protect the nerves of the central nervous system, arachnoiditis may cause chronic nerve pain as well as bowel, bladder, or sexual dysfunction. Arachnoiditis is often the unintended consequence of a medical procedure involving the spine, but may also result from infections and other conditions.

A physiotherapist holding spine model
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Symptoms

The arachnoid is the middle layer of the meninges, the three membranes that encase the brain, spinal cord, and nerve roots. (The other two are the outer dura mater and inner pia mater.) The swelling of the arachnoid that defines arachnoiditis places direct pressure on spinal nerves. Resulting symptoms can vary based on the location and severity of the inflammation.

There is no consistent pattern of symptoms with arachnoiditis. In some cases, the condition may be subclinical (i.e., with few overt symptoms). At other times, the condition can be debilitating, although it is rarely considered life-threatening.

In many cases, symptoms only arise months or years after the instigating event.

Arachnoiditis is primarily characterized by neuralgia, a sharp and often shocking pain that follows the path from a nerve root.

The condition can become chronic due to the rapid formation of scar tissue that causes spinal nerves to stick together and malfunction. This can lead to a cascade of symptoms, including:

  • Numbness or tingling in the legs
  • Severe shooting pains in the back and legs
  • Leg weakness
  • Burning feet
  • Headaches
  • Crawling or "dripping" sensations on the skin
  • Muscle spasms, cramps, and twitching
  • Episodes of blurred vision
  • Episodes of overheating or sweating
  • Difficulty urinating or defecating
  • Erectile dysfunction

Complications

Symptoms can become severe and even permanent if the scar tissues begin to calcify (harden like bone), leading to a rare complication known as arachnoiditis ossificans.

In such cases, chronic nerve pain can be accompanied by symptoms such as:

  • Loss of bladder or bowel function
  • Impairment of fine motor skills, such as writing
  • Difficulty walking
  • Inability to sit or stand for long periods
  • Lower-extremity paralysis

Sadly, symptoms like these are usually not reversible and can even be progressive, resulting in significant disability and a reduction in quality of life.

Causes

Arachnoiditis is usually due to some kind of direct or indirect injury to the spine. This could be a physical intervention or an infectious, inflammatory, or neoplastic (tumor-forming) condition. In many cases, it arises from a medical spinal procedure.

Some of the most common causes of arachnoiditis include the following.

  • Complications of spinal surgery or injuries to the cervical spine can increase the risk of neuralgia, while injuries to the lumbar spine can cause motor paralysis and the loss of bladder and bowel function.
  • Misplaced epidural injections, in which a steroid, anesthetic, or other injected medication is accidentally trapped in the dura mater
  • Multiple lumbar punctures (spinal taps), which can promote bleeding, spinal epidural hematoma (bruising), and arachnoidal fibrosis (scarring)
  • Spinal cord infections, such as viral or fungal meningitis or bacterial tuberculosis
  • Chronic spinal compression caused by advanced spinal stenosis or degenerative disc disease
  • Spinal trauma resulting in an intrathecal hemorrhage (bleeding within arachnoidal and adjacent membranes) and arachnoidal fibrosis
  • Spinal neoplasms (benign or malignant tumors) involving or compromising the arachnoidal membranes

Certain injected dyes used in myelogram imaging studies have been known to cause arachnoiditis, although the agent most commonly associated with the condition—Myodil (iophendylate)—has been discontinued due to safety concerns.

In recent years, there have been suggestions that certain people have a genetic predisposition for arachnoiditis, although the exact chromosomal mutations have yet to be identified.

Although arachnoiditis is still considered rare, the exact incidence of the disease remains unclear. Some experts believe that the increased use of invasive and non-invasive spinal procedures, now considered commonplace, may contribute to a perceived rise in the number of arachnoiditis cases.

Diagnosis

Arachnoiditis can be difficult to diagnose, in part because its symptoms are similar to those of many other conditions. More often than not, people will seek treatment for arachnoiditis when the disease is advanced simply because symptom onset was delayed.

Arachnoiditis is generally suspected when multiple symptoms are present—for example, chronic neuralgia, which may be accompanied by weakness and bladder dysfunction.

Physical Exam

The diagnosis of arachnoiditis will typically begin with a review of your symptoms and medical history (including past procedures and illnesses). A physical exam will include an evaluation of your reflexes as well as the range of motion of your legs.

People with arachnoiditis will often lack the ability to extend their legs fully (a key diagnostic clue) and will take short, guarded steps when walking.

Lab Tests

Arachnoiditis is characterized by a chronic neuroinflammatory response. This can often be detected with blood tests that measure generalized inflammation in the body.

Chief among these is a test called erythrocyte sedimentation rate (ESR), which measures the speed by which red blood cells settle to the bottom of a test tube. Faster sedimentation indicates higher levels of inflammation. Another test, called the C-reactive protein (CRP) test, measures the level of a protein produced by the liver in response to inflammation.

Together, these tests cannot diagnose arachnoiditis, but may be able to support a diagnosis.

Imaging Studies

While the tests above will invariably be performed, imaging studies are generally the most effective way to diagnose arachnoiditis.

Among the possible options is a computed tomography (CT) scan, in which a series of X-ray images create three-dimensional "slices" of the body. Studies have shown that CT imaging is better able to detect calcification without the need for a contrast agent. A CT scan can also confirm conditions like degenerative disc disease.

In the past, the injection of oil-based contrast agents between the spinal bones could cause adhesive spinal cysts called syringomyelia. Today, these agents have largely been replaced by water-soluble contrast agents.

Magnetic resonance imaging (MRI) scans⁠—which use magnetic and radio waves to create highly detailed images of soft tissues⁠—is the most sensitive test to view the clumping of the nerve roots associated with arachnoiditis. MRIs are also well-suited to detect soft-tissue abnormalities like a spinal cord tumor.

Another useful study is an electromyogram (EMG), which can assess the severity of nerve root damage by measuring electrical activity. Newer contrast dyes used in CT myelograms are not associated with an increased risk of arachnoiditis.

Lumbar Puncture

If an infection is suspected, a lumbar puncture (spinal tap) may be ordered to extract a sample of cerebrospinal fluid for evaluation in the lab. The procedure can also help differential arachnoiditis from an epidural abscess, a localized collection of pus that can usually be treated with a course of antibiotics.

Treatment

There is no cure for arachnoiditis. Treatment is focused on the control and alleviation of chronic nerve pain.

The approach is not unlike those used to treat other chronic pain disorders, such as fibromyalgia, although a single approach has yet to prove consistently effective in all cases.

Unfortunately, the disease can often be life-altering even with consistent treatment.

Medications

Depending on the severity and location of the symptoms, certain drugs may be prescribed to help control neuralgic pain and other symptoms. The options are broadly categorized as:

  • Anti-inflammatory medications such as the oral immunosuppressant drug prednisone, the injected nonsteroidal anti-inflammatory drug (NSAID) ketorolac, and the oral NSAID (Tivorbec) indomethacin
  • Analgesic pain killers such as the opioid drug fentanyl, low-dose anesthetics like ketamine, or topical analgesics like lidocaine or prednisone
  • Neuropathic drugs like Lyrica (pregabalin) and Neurontin (gabapentin), which are often used to treat post-shingles neuralgia and diabetic neuropathy
  • Tetracycline antibiotics like Minocin (minocycline), which suppress glial cells that surround neurons and, by doing so, help temper neuropathic pain
  • Diuretics like Diamox (acetazolamide), which help reduce cerebrospinal fluid pressure caused by neuroinflammation, thereby reducing pressure on nerve cells

Epidural steroid injections, a procedure explored by some to treat lumbar arachnoiditis, are not recommended due to the risk of epidural bleeding, which would only increase⁠—rather than decrease⁠—the severity of symptoms.

Pain Management

As a chronic and sometimes permanent condition, arachnoiditis is rarely treated with medications alone. Instead, doctors will typically recommend a combination of medications, physical therapy, and routine exercise to help minimize pain while preserving the range of motion of your lower extremities.

Psychotherapy may also be recommended to teach you how to cope with chronic pain. This may involve mindfulness-based stress reduction and medications that help treat acute anxiety or depression.

Mobility devices may also be considered. Standing wheelchairs and Segways are especially useful, since they help you remain upright. However, both are costly and rarely covered by health insurance.

Developing Approaches

Surgery, including a surgical nerve block, is rarely used to treat arachnoiditis due to high failure rates. However, newer techniques like spinal cord stimulation (SCS) are demonstrating positive results in some.

A spinal cord stimulator is an implanted device that sends electrical impulses into the spinal cord to help relieve certain types of pain. Also known as a dorsal column stimulator, the device reduces the excitability of neurons and, by doing so, interferes with the delivery of nerve signals to the brain.

SCS is used to treat other types of chronic pain, but is only considered when other conservative therapies fail to provide relief.

A 2015 study published in the Journal of Pain reported that SCS used in a single patient with arachnoiditis (who did not respond to the opioid drug oxycodone or other treatments) delivered complete pain relief following the implantation. Within a month, no other treatments were needed. Further research is needed to support these findings.

Despite the potential benefits of SCS, complications are not uncommon and may include infection, epidural hematomas, cerebrospinal fluid leakage, nerve injury, and, on rare occasions, paralysis.

Because of this, SCS should be considered a last-resort option after weighing the risks and benefits with a surgeon who performs these procedures regularly.

A Word From Verywell

The causes of arachnoiditis are many and, as such, are not easily avoided. With that said, you do have the option to question whether any spinal procedure is absolutely necessary. In some cases, a doctor may be able to recommend an alternative procedure or therapy.

With that said, you should never avoid spinal procedures that are vital to your good health. Just be sure to ask your doctor if other options are available and the pros and cons of each of them. By keeping an open mind and asking the right questions, you can usually make the most informed choice.

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