Arachnoiditis Part 1: Clinical Description
Mention the word “arachnoiditis” to experienced clinicians, and they are liable to ask, “What is it?” or state, “I’ve not heard of it.” It is no wonder that it is a poorly known disease because it is listed as “rare” by the National Organization for Rare Disorders. To those of us who deal with severe, intractable pain, however, arachnoiditis is well-known. It ranks at the top of the list of “worst pain conditions,” along with metastatic bone cancer, renal colic, chronic regional pain syndrome, and migraine. The most severe cases of arachnoiditis produce the worst form of lumbar pain. There are less severe cases, and pain practitioners might have encountered these patients without realizing it.
We prepared this article because arachnoiditis, unfortunately, has become more common in recent years. It is caused by any rupture, trauma, or infection that penetrates the dural lining of the spinal cord. Counted here are accidents that occur with epidural injection, trauma including that from war injuries and auto accidents, and spine surgery. The first part of this 2-part series is a clinical description of adhesive arachnoiditis (AA). Part 2 describes cases to illustrate measures to help improve patient quality of life.
Axial view of the MRI of the lumbar spine demonstrating ehhanced nerve roots (black arrows). Image courtesy of Dr. J. Antonio Aldrete.
The Function of Arachnoid Matter
The protective covering of the spinal cord consists of 3 meninges: the dura (outer layer), arachnoid, and pia (inner layer). Under the microscope, the fibers and filaments that make up the arachnoid layer resemble a spider web, hence the derivation of the name. If this layer becomes inflamed, it is called arachnoiditis. Between the arachnoid and the inner layer is the subarachnoid space, in which flows the cerebrospinal fluid (CSF) that is secreted within the ventricles of the brain (fluid-filled spaces deep inside the brain) and the ependymal cells lining the cerebral subarachnoid space. CSF circulates in the subarachnoid space, being absorbed into the venous sinuses via the arachnoid granulations and into the lymphatic system through spinal nerve-root pockets. The fluid provides a protective cushion between the brain and the skull, bathing the nervous system with nutrients and removing waste products.
Impaired CSF flow prevents this natural exchange from taking place, to the detriment of the affected nerve roots. The entire volume of CSF is produced, absorbed, and replaced about 3 times per day in a continuous manner. If flow is impeded, fluid can build up, causing increased pressure and pain. Additionally, an inflamed arachnoid lining may entrap nerve roots, scarring them and other neural elements inside and around the spinal canal. When this occurs, the term AA generally is used. Such adhesions within the spinal canal can disrupt many functions of nerves that lead to the extremities, bladder, bowel, and sex organs. Unbearable, suicide-provoking pain can result.
Arachnoiditis now is defined in medical dictionaries. It even has an International Classification of Disease, Ninth Edition (ICD-9) diagnostic code number. Dorland’s Medical Dictionary defines “chronic adhesive arachnoiditis” in a meaningful clinical way: “thickening and adhesions of the leptomeninges in the brain or spinal cord, resulting from previous meningitis, or other disease process or trauma; it is sometimes secondary to therapeutic or diagnostic injection of substances into the subarachnoid space. The signs and symptoms vary with extent and location.”
Note that the above definition states the 3 major causes of AA: infection, trauma, and injections of foreign substances (chemical). The most common form of trauma is surgery, and pain patients who have undergone multiple spine surgeries should be suspected of AA if they have the symptom profile described in Table 1.1,2 The same applies to pain that occurs following an epidural injection.
The cauda equina is the terminal portion of the spinal cord and the spinal nerves below the first lumbar nerve. “Cauda equina syndrome” is a term sometimes used to describe the patient who has AA and manifests loss of bowel, bladder, or sexual function, or has paraplegia.
The first wave of cases of AA occurred about 20 to 30 years ago, when pantopaque dye was used for myelograms. When use of this contrast material gave way to magnetic resonance imaging (MRI), new cases of AA dramatically decreased.
The new wave of cases of AA primarily have resulted from the widespread use of epidural corticosteroid injections.3,4 Fortunately, AA is a rare complication of epidural injections, which have increased by 130% from 2000-2011, or an annual increase of 7.3%.5 Unfortunately, the dura can be punctured accidentally during an epidural, exposing the arachnoid membranes to a foreign substance and/or infectious agent.3
In September 2012 a tragedy occurred, forcing AA into the limelight. A large, multistate outbreak of fungal meningitis occurred that was traceable to 3 lots of preservative-free methylprednisolone produced by the New England Compounding Center (NECC), in Massachusetts.3,4 The offending agent was a mold known as Exserohilum rostratum. This fungus normally is an opportunistic agent that only attacks immunocompromised or immunoincompetent human hosts. In the outbreak, 751 cases of central nervous system (CNS) infections with E rostratum were documented, and 64 persons died. An unknown percentage of these cases went on to develop AA.3,4
Between the fungal outbreak and the rare accidents of epidural injection, numerous lawsuits have been filed across the United States. Patients and families with AA are lobbying the FDA to ban epidural injections, and the FDA has appointed a task force to study the use of epidural corticosteroid injections. In April 2014, the FDA issued a safety warning that “injection of corticosteroids into the epidural space of the spine may result in rare but serious adverse events, including loss of vision, stroke, paralysis, and death.”6
While the author recognizes the controversies and supports the study of AA, our main intent is to educate pain practitioners about AA and call upon them to recognize it and intervene as early as possible. It is the author’s personal experience with AA that certain, early measures can prevent the progression of AA.