THE ADHESIVE ARACHNOIDITIS SYNDROME

THE INFLAMMATORY NATURE OF ADHESIVE ARACHNOIDITIS

Arachnoiditis is chronic inflammation of the arachnoid layer of the meninges which consists of trabeculae, a mesh of interwoven collagen fibrils resembling tissue paper. These secrete spinal fluid, which circulates through the cerebrospinal axis and is absorbed through the arachnoid villi in the brain.

The initial phase of the inflammatory process involves influx of white blood cells in response to an insult to the subarachnoid space, such as blood (trauma, surgery), foreign substance (dye, etc) or infectious agent (e.g. meningitis). This is initiated via the action of cytokines, (proteins that act as immune modulators). There is infiltration by macrophages and mesenchymal cells; the latter transform into fibroblasts, which make collagen (scar tissue).

Usually the fibrinolytic process, which breaks down excess scar tissue, limits this, but in arachnoiditis the scar tissue continues to form.

Authors such as Jayson ([4]) have suggested that there may be a defect in the fibrinolytic pathway.

The neurosurgeon Mayfield, through his research in the 1980s, felt that there might be an immune response that is responsible for the degree of reaction, especially to chemical insult. Frank et al cultured arachnoidal cells in vitro and demonstrated their immune capabilities. ([5])

A further interesting point to note is that some features of arachnoiditis are suggestive of Chemically Induced Immune System Disorder, as described by The National Foundation For the Chemically Hypersensitive in 1989. This disorder is a complex, multisystem condition that results from toxic exposure. This causes chemical poisoning, that provokes an immune response, which in turn may lead to development of autoantibodies.

Furthermore, there may be a “spreading phenomenon” which leads to multiple sensitivity, to a variety of substances e.g. petroleum products, phenol, pesticides, detergent enzymes and synthetic fragrances. This scenario might explain why some patients with arachnoiditis after myelogram or epidural steroid exhibit signs of multiple chemical hypersensitivity. (See under Symptomatology and Iatrogenesis). Indeed, there is an argument for hypothesising that the cases with diffuse arachnoiditis and widespread symptoms outside the CNS are due to a form of Chemically Induced Immune System Disorder i.e. a toxic phenomenon.

Anecdotal evidence suggests that a number of patients with arachnoiditis also have autoimmune type symptoms (See below) and/or a diagnosed coexisting autoimmune disorder such as Sjogren’s syndrome, Rheumatoid Arthritis, Systemic Lupus Erythematosus. These conditions are known to be associated with vasculitic neuropathies.

Also, Rheumatoid arthritis and various other connective tissue diseases show features of fibrosis (see Appendix I).

It therefore seems reasonable to hypothesise that arachnoiditis may be an autoimmune condition, possibly involving antibodies that affect the fibrinolytic pathway, such as antiplasminogen antibodies (seen in Rheumatoid Arthritis), in response to an insult to the arachnoid meninges, especially when that insult is chemical in nature.

There have been several papers recently discussing the possible role of previous viral infections, particularly Epstein-Barr virus (EBV) in the aetiology of autoimmune disorders such as Sjogren’s syndrome, and Systemic Lupus Erythomatosus ([6]). Many patients with arachnoiditis have had previous viral infections, including EBV and Cytomegalovirus (CMV). It is possible that this has some significance in the development of an autoimmune component to arachnoiditis, which could account for the degree of severity of the condition in that group of patients.

MacDonald ([7]) noted that 18% of the general population carry a factor in the blood (Histamine Release Factor HRF) which causes a dramatically potentiated, sustained autoimmune reaction to foreign substance in the people who carry this factor. As this factor may be implicated in autoimmune responses, this may be relevant in explaining why there is only a minority of patients with arachnoiditis who develop the condition to a clinically significant degree.