Arachnoiditis is a disorder caused by the inflammation of the arachnoid. The arachnoid is one of the membranes that surround and protect the nerves of the spinal cord. The arachnoid can become inflamed because of:

• An irritation from chemicals
• Infection from bacteria or viruses
• Direct injury to the spine
• Chronic compression of spinal nerves
• Complications from spinal surgery or other invasive spinal procedures (procedures that involve breaking the skin)

Inflammation can sometimes lead to scar tissue or scar adhesions, which cause the spinal nerves to “stick” together.

If arachnoiditis begins to interfere with the function of one or more of the spinal nerves, it can cause a number of symptoms, including chronic and persistent pain, numbness, tingling, and a characteristic stinging and burning pain in the lower back or legs. 

Some people with arachnoiditis will have debilitating muscle cramps, twitches, or spasms.  It may also affect bladder, bowel, and sexual function. In serious cases, arachnoiditis may cause the lower limbs to be paralyzed.

Arachnoiditis remains a difficult condition to treat, and long-term outcomes are unpredictable. Most treatments focus on relieving chronic pain and improving symptoms that affect a person's daily functioning. 

Doctors often recommend a combination of pain management, physical therapy, exercise, and psychotherapy (talk therapy).  Results of surgery for arachnoiditis are generally poor and give only short-term relief.

Arachnoiditis has many possible causes, including:

• mechanical injury during spinal surgery, or complications from spinal surgery (about 60% of cases)
• trauma to the spinal cord
• one or more spinal taps
• steroid epidural injections or other injections
• spinal and epidural anesthesia
• myelography
• bacterial or viral spinal infections

The initial symptoms of arachnoiditis are caused by inflammation of the arachnoid, and the formation of scar tissue and adhesions later cause the more severe symptoms as the condition progresses.