What is arachnoiditis?

Arachnoiditis describes a pain disorder caused by the inflammation of the arachnoid, one of the membranes surrounding and protecting the nerves of the spinal cord. The arachnoid can become inflamed due to irritation from chemicals, infection from bacteria or viruses, direct injury to the spine, chronic compression of spinal nerves, or complications from spinal surgery or other invasive spinal procedures. Inflammation can sometimes lead to the formation of scar tissue and adhesions, which cause the spinal nerves to "stick" together. Arachnoiditis can interfere with the function of one or more of these nerves and cause 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 severe cases, arachnoiditis may cause paralysis of the lower limbs.

This answer is based on source information from The National Institute of Neurological Disorders and Strokes.