Arachnoiditis: Diagnosis and Treatment
Arachnoiditis is a progressive neuroinflammatory disease.1-3 Although recognized many years ago, heretofore it has been considered a rare disease and is listed in the “Rare Disease Registry.”2,3 I first introduced readers to the term adhesive arachnoiditis (AA) in the August 2014 issue of Practical Pain Management.3 Today, we expand our coverage of the condition, which is, for many reasons, increasing in incidence and prevalence.
Although the term arachnoiditis simply implies inflammation of the arachnoid lining of the meninges or thecal sac, the major pathologic abnormality in the majority of cases is neuroinflammation of the nerve roots in the cauda equina.4-8 Once glia cells in nerve roots produce neuroinflammation, they may form adhesions and scars that may cause nerve roots to stick together or clump and adhere to the arachnoid lining.9-13
The term AA is the term historically assigned to the condition when adhesions or scarring between nerve roots and/or the arachnoid lining is visible on magnetic resonance imaging (MRI).2,12 AA will be the term used throughout this paper as it is this stage of the disease that usually causes a patient to seek medical and pain treatment.
Although neuroinflammation and adhesion formation may naturally resolve in some patients, AA may be a crippling, progressive, painful condition of immense severity.6,14-17 It may progress to lower extremity paralysis; bladder, bowel and gastrointestinal dysfunction; inability to sit or stand for long periods of time; deterioration of mental abilities; and create an autoimmune disorder with symptoms that mimic classic rheumatologic disease.3
Over the past 5 years, my clinic has admitted to treatment an increasing number of patients with AA. Today, the practice follows about 65 cases. I have reviewed the MRI’s from over 200 confirmed patients. Some of the cases were accepted as emergencies because they developed severe pain and partial paralysis of the lower extremities and bladder dysfunction immediately after a spinal tap, epidural anesthesia given for childbirth, epidural corticoid injection, or surgery.
Little has been written about the clinical diagnosis and treatment of arachnoiditis.2,3 Much of what is written here is the author’s personal observations, beliefs, and methods as there are few supporting references in the literature.
Anatomy of the Spinal Cord
Understanding AA requires some knowledge about the anatomy of the cauda equina, or “horse’s tail.” About two dozen nerve roots emanate and hang down from the end of the spinal cord known as the conus medullaris (Figure 1).18,19 The nerve roots within the thecal sac are quite organized. They are primarily in the posterior portion of the thecal sac between L1 to L3 and then move forward or anterior (Figures 2 and 3). The nerve roots progressively exit the thecal sac beginning between L1 and L3.
Nerve roots of the cauda equina are constantly bathed and submerged in spinal fluid that acts as a lubricant against friction between nerves, transports waste products, and brings nutrients to the nerve roots.20-24 The spinal fluid turns over about 4 times a day.20 Therefore, waste products, including inflammatory particles from inflamed nerve roots, are carried upward to drain through channels in the meninges into cervical lymph nodes and general circulation.21-23
To illustrate how neuroinflammation affects the spinal cord, we turn to a rare, but devastating example. Cauda equina syndrome is a serious neurological emergency that can have devastating long-lasting neurologic consequences. This diagnosis is given when anatomical tissue, from a malignant mass or an intervertebral disc or collapsed vertebrae, acutely compresses the nerve roots of the cauda equina. When cauda equina compression occurs, it is a neurosurgical emergency because the nerve roots must be released to prevent lower extremity paraparesis, paralysis, bladder and bowel impairment, and severe pain.
Although the term cauda equina syndrome has traditionally only referred to the acute compression of the nerve roots, some practitioners have used the term “chronic cauda equina syndrome” when bladder and bowel dysfunction, pain, and some paraparesis coexist.25-27 In addition, cauda equina syndrome is a rare but well-recognized complication of longstanding ankylosing spondylitis. A number of case reports have shown linked arachnoiditis in the pathogenesis of the cauda equina syndrome of ankylosing spondylitis.28,29 As far as I can determine, the term chronic cauda equine syndrome is not due to nerve root compression but, rather, neuroinflammation of the nerve roots in the cauda equine—in effect, it may be considered an alternate name for AA.
The Inciting Cause: Irritation and Neuroinflammation
AA is primarily found in the lumbar-sacral spine, although it also may occur in the cervical and thoracic spines.7,9,10,16,17,30 Traditionally, the diagnosis of AA has been made on MRI, where nerve roots in the cauda equina can be seen to have formed adhesions between each other, forming clumps, and/or when adherence to the arachnoid lining is caused by adhesions.5-11
AA may originate with any irritant that may affect some of the 2 dozen nerve roots in the cauda equina.14,31 The irritant may be a toxin, trauma, infection, or friction between nerve roots.4,10,12,15,31 Once irritation occurs in the nerve roots, activated glial cells initiate a neuroinflammatory response.32-34 Like all inflammation, a modest amount is protective and curative, but too much causes tissue destruction with adhesive and scarring elements.
Common pathologic conditions of the spine, including herniated discs, spinal stenosis, and degenerative arthritis, may cause enough irritation to produce neuroinflammation in cauda equina nerve roots in the lumbar region. Despite the lubricating properties of spinal fluid, spine deformities and imbalances produced by scoliosis, cysts, or arthritis may cause enough compression and friction between nerve roots to cause irritation, activation of glia cells, and neuroinflammation.
The trauma of medical procedures, including paraspinal injections and surgeries that are medically indicated, may leave AA behind as a complication.4,6,15,17,25,26 Although the percentage is unknown, many patients who are now labeled with “failed back surgery syndrome” likely have AA and should be evaluated for this condition.