Hello @parus. Here is what I was able to find out about arachnoiditis, which is still in the process of being researched.

Arachnoiditis is a pain disorder caused by the inflammation of the arachnoid, one of the membranes that surround and protect the nerves of the spinal cord. Severe stinging, a “burning” pain, and neurological problems characterize the condition. The arachnoid can become inflamed from any of the following: Direct injury to the spine, Chemicals, Infection from bacteria or viruses (viral and fungal meningitis or tuberculosis), Chronic compression of spinal nerves, and Complications from spinal surgery or other invasive spinal procedures.

Arachnoiditis can be diagnosed using a CAT scan, MRI, and a few others.

@missroz, your experience sounds rather frustrating. You mentioned that it was diagnosed during a procedure, was that documented in your records? @jimhd is right, sometimes patients have to be his or her own best advocate. Mayo Clinic released posted a story earlier this year about the benefits of second opinions, https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-researchers-demonstrate-value-of-second-opinions/. @missroz, have you thought about getting a second opinion?