describes a pain disorder caused by the inflammation of the arachnoid, 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, as the result of 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 ÒstickÓ together. If arachnoiditis begins to interfere with the function of one or more of these nerves, it can cause a number of symptoms, including numbness, tingling, and a characteristic stinging and burning pain in the lower back or legs. Arachnoiditis is difficult to treat and long-term outcomes are unpredictable. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.