Adhesive Arachnoiditis:A Continuing Challenge
This little known and poorly understood condition has a reputation amongst medical personnel as a rare entity, or maybe even a non-existent one.1 However, far from being a medical dinosaur, adhesive arachnoiditis, the clinically significant form of the disease, is a ‘clear and present danger’ that practitioners need to be aware of since it remains a life sentence of unremitting pain and disability imposed, in some cases, very early in life.
Historically, adhesive arachnoiditis was first recognized over a hundred years ago and was originally principally linked with spinal infections such as TB and thoracic involvement was the typical presentation. However, iatrogenic arachnoiditis, involving the lumbar region, has since been associated with the use of oil-based myelogram dyes such as iophendylate (Pantopaque/Myodil).2
Many doctors, if aware of the condition at all, tend to link it with Pantopaque/Myodil and thus to consider it a past threat rather than a continuing one. This is sadly not the case. First, one must bear in mind the prolonged usage of the oil-based dyes up until the late 1980s, and the possibility of considerably delayed onset of symptoms, maybe some 15-20 years later. In fact the delayed onset can lead to a lack of recognition of the true cause of the symptoms, which may be triggered by a relatively minor event such as a fall or slight car accident. The ensuing deterioration appears completely out of proportion, but may in fact be a result of disruption of cysts releasing residual dye to act as a potent nerve irritant, especially if there is also blood within the subarachnoid space.
It is important to note that the current practice of placing a number of different chemotherapeutic agents in or near the cerebrospinal fluid space is relatively commonplace, despite this area being highly vulnerable to damage. In some cases, the treatment is lifesaving (leukemia) but in others, such as intraspinal steroid injections for low back pain, the true risks may often be underestimated and preclude an accurate assessment of risk-benefit.
One of the major difficulties with this condition is the lack of accurate data on incidence and prevalence.3 The known cases are likely to constitute the proverbial tip of the iceberg. In addition, we remain ignorant of the number of people currently going about their lives, symptom free, but carrying a ‘time bomb’ within them that could be triggered by some relatively mild initiating event, and lead to a major and enduring impact on their quality of life.
A common myth about arachnoiditis is that it is simply a spinal condition. During the author’s research over the past six years, it has become clear that adhesive arachnoiditis is syndromic in nature. One of the problems encountered in diagnosing many patients is the multifactorial nature of the disease’s etiology together with a complex clinical picture comprising the effects of pathological damage, secondary features, and the progression of any underlying condition such as degenerative disc disease.
Furthermore, we are constrained by difficulties identifying the condition because medical evidence may be lacking or fails to correlate with the clinical picture, and much of the medical literature on the subject tends to deal only with the most severe end of the spectrum.4 Clinicians may often fail to recognize the disease5 and this can reinforce the notion that this this disease is rare.
Medically this disease appears to remain in something of a ‘fog’ of imprecise information, but there is an urgent need for co-ordinated research. Unfortunately, the iatrogenic aspect of the majority of cases further muddies the waters and perhaps complicates initiation of medical research that this disease warrants. At this time, the way forward remains unclear.3
Typical Disease Progression
Arachnoiditis is inflammation of the arachnoid layer of the meninges. Generally medical use of the term refers to a chronic inflammation, because acute arachnoiditis is virtually indistinguishable from meningitis clinically. When the arachnoid membrane is damaged, whether by trauma (accidental or surgical), chemical injection or infection, there is an inflammatory reaction much as there is in any part of the body. In adhesive arachnoiditis, however, the healing process, which involves deposition of scar tissue, is inefficient or may be repeatedly impaired when the insult/damage is ongoing. This means that excess scar tissue forms.
Effectively there are three main stages of arachnoiditis as follows:
- First Stage — Radiculitis: The spinal nerve roots are inflamed in response to an event such as surgery in the area and the adjacent blood vessels distended (hyperaemia). The subarachnoid space is encroached upon by the swollen nerve roots and practically disappears. Deposition of collagen fibrils begins. Substances in the body involved with inflammation can sensitize nerves, and these nerves begin to fire abnormally.
- Second Stage — Arachnoiditis: The scar tissue increases, and the nerves begin to adhere to each other and the dura. At this stage they begin to resemble strands of overcooked spaghetti sticking to each other and local tissue.
- Third Stage — Adhesive Arachnoiditis: This involves complete encapsulation of the nerve roots by scar tissue with the subsequent smothering causing them to atrophy. The scarring prevents contact with surrounding spinal fluid and severe adhesive arachnoiditis may be obliterative, causing completely impeded CSF flow within the affected area. The isolated nerve roots are therefore starved of oxygen and nutrients and waste products of metabolism accumulate. There may be cysts containing CSF or oil-based myelogram dye. There may also be calcification or ossification of the affected tissues.
Spinal adhesive arachnoiditis may be either localized or diffuse. Generally speaking, arachnoiditis from mechanical causes such as surgery tends to be more localized, whereas that caused by chemical insult may be more diffuse and widespread.
As the blood supply to the nerve roots is increasingly impaired, neurophysiological compromise results in pain and other neurological symptoms
Cerebral arachnoiditis affecting the brain is relatively uncommon and is usually related to infections (meningitis), trauma, tumor, intracranial haemorrhage and chemical insult (myelogram dyes). It was reported by Horrax6 as early as 1924 when symptoms suggestive of a tumor turned out to be arachnoiditis in the cisterns.
The most common cause of cerebral arachnoiditis is infection, whether local (within the central nervous system) or in other parts of the body, particularly the sinuses and the middle ear. Tuberculous cerebral arachnoiditis has been shown to arise in the absence of pulmonary infection. The parasite cystercicosis can also cause this type of arachnoiditis.
Complications of arachnoiditis include arachnoid cysts, syringomyelia and hydrocephalus.