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As far as medical history is known, it is likely that arachnoiditis (ARC) was present in the spines of some Egyptian mummies (estimated to have been buried over 5,000 years ago) in whom typical lesions of spinal tuberculosis were found. This dreadful disease is characterized by longstanding inflammation of the two innermost layers of the sac surrounding the spinal cord (SC) which contains the cerebrospinal fluid (CSF), and not uncommonly expands into the nerve roots, and the cauda equina, occasionally deforming the dural sac (DS) by scarring.


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ARACHNOIDITIS: AN UPDATE IN THE YEAR 2000

ORIGIN

The usual causes of spinal arachnoiditis are:

1.       Infections like tuberculosis, AIDS, fungus 

     (cysticercosis) and meningococcus, etc.

2.       Dyes used for myelograms like pantopaque, metrizamide, omnipaque, etc.

3.      Blood entering the spinal sac, i.e. from subarachnoid hemorrhage, epidural blood patches, bleeding from anticoagulants, etc.

4.      Spinal surgery, mostly from rents (recognized or unrecognized) of the dura with blood entering the sac (this is the most common cause today), direct SC or nerve root injury.

5.      Irritant compounds injected into the sac such as hypertonic saline, phenol, methotrexate, hyaluronidase, papain, etc.

6.      Preservatives contained in some medications injected into the spine such as polyethylene glycol, benzylic alcohol, para-aminobenzoic acid, etc.

7.      Traumatic injury to the SC or the brain may result in bleeding into the CSF, nerve tissue damage or avulsion. Even needle punctures causing paresthesia on the nerve roots or the SC (from peridural, spinal anesthesia or other nerve blocks) may cause ARC.

TOPOGRAPHY

Cerebral ARC may occur in the optic chiasm (usually from sinus infection) and in the lateral and posterior fossae of the skull (from chronic ear infections or parasites).

Spinal ARC may appear as localized when it is at one intervertebral level; diffuse as from infiltrating tumors of the spine; distant when subarachnoid hemorrhage in the brain may result in spinal ARC; segmental when it is present in two or more separate levels; and contiguous if it includes two or more adjacent vertebral levels of the spine.

Cauda equinoid and cauda equina syndromes are mild and moderate lesions located on the distal point of the SC are truly varieties of ARC, as well as syrinx (loss of most of the normal pattern and mapping of the SC), syringomyelia representing cavitary lesions, and pseudomeningocele consisting of secondary, thin, false sacs adhered to or behind the dura (usually containing some nerve roots)—all are different presentations of ARC.

PATHOLOGICAL PROCESSES

This is indeed a complex illness because in the majority of these patients, ARC occurs as an iatrogenic complication from either a diagnostic (myelogram) or a therapeutic (laminectomy) procedure. So, both the symptoms and the radiological findings are superimposed to the patient’s disease that motivated the intervention, making a specific profile for ARC difficult to define, if not impossible.

Immediately after the injurious event, an acute inflammation takes place next to and adjacent to the site of entry, depending on the extent and volume of irritant in relation to the volume of the CSF and hydration of the patient. Depending on the location, radiculitis may be the earliest manifestation, with swelling of the nerve roots that became in greater contact with the offending agent. Swelling of the adjacent arachnoid creates acute arachnoiditis with increased vascularity, venous congestion, and hyperemia. This inflammatory phase either progresses and becomes more severe and more extensive (especially if repeated insults occur and/or the patient’s immune system hyperreacts) or it may gradually subside, especially if anti-inflammatory (steroid and non-steroid) agents are administered.

After an interval of 4 to 7 months, the syndrome may move into a proliferative phase when collagen and fibroblasts appear, gradually forming adhesions, fibrosis and scarring which make nerve roots adhere to each other and to the meningeal sac, which may also be deformed in a constrictive manner (obliterative arachnoiditis) to the point of obstructing the DS, partially interfering with the normal flow of CSF, or obliterating it completely as in pachymeningitis.

DYSFUNCTIONAL EVENTS

Throughout these processes, the affected nerve roots generate exaggerated electrical impulses to the dorsal horn of the SC, where a complex system of receptors, inhibiting pain pathways, and neuron connections are located. These exaggerated impulses eventually make the receptors oversensitive, and may interfere with inhibitory relays to the point that pain is perceived to be of greater and greater intensity, which creates a self-feeding mechanism, expands to adjacent areas, and appears to increase in intensity (“wind-up” phenomenon and distribution). It may also produce severe muscle spasms when ventral roots are affected. There is evidence that the sympathetic nervous system is affected, represented by sweating, heat intolerance, trophic changes, night sweats, low-grade fever, etc.

MANIFESTATIONS

The symptoms vary, but pain is the predominant complaint—most frequently burning sensations (92%), throbbing and sharp pains on the lower back, legs and feet. Numbness and tingling sensations are frequent, while atypical headaches, blurred vision and insomnia seem to be systemic manifestations. Bladder dysfunction is prevalent mainly in women (incontinence).  Rectal dysfunction is less common, but sexual (organic and emotional) dysfunction is more prevalent. Psychological manifestations are frequently seen in patients with chronic pain; in patients with ARC, depression is common in about 80% of them secondary to despair, hopelessness, fear of income loss, and/or family disputes, in some cases leading to thoughts of self-injury.

RADIOLOGICAL DIAGNOSIS

Current technology allows for prompt and precise diagnosis of the characteristic lesions of ARC; specifically, MRI defines the location and the extent of intraspinal (intra and extradural) pathology. Thickened and swollen nerve roots and cauda equina can be identified as early as one or two days after the injurious event. Clumped nerve roots may not be seen until months later, indicating a maldistribution of the usually orderly mapping of the roots located at the most dependent portion of the dural sac, surrounded by and floating in CSF at the lumbar region. In worse cases, deformities of the dural sac, adherence of the roots to the sac wall, fibrosis and scarring may appear. CAT scans may show skeletal, ligament and muscle abnormalities, and extradural intraspinal lesions, but only when it is preceded by myelography would intradural structures be recognized (except calcifications). The author is against the risk of unnecessary myelograms, but when metal hardware is present, since the diagnosis is crucial, this method may have to be used, as long as water-based dyes are injected. It is acknowledged that this type of contrast media may also produce ARC. The expertise of the radiologist interpreting the films is imperative to achieve a precise diagnosis of ARC, and adequate hydration of the patients will ensure reduced concentration of the dye used.

TREATMENT

Unfortunately, there is no cure for arachnoiditis. In the acute inflammatory phase of ARC, the administration of systemic and intraspinal corticosteroids may prevent the evolution into the chronic phase. Pain may be treated with indomethacin, dipyrone or ibuprofen; in addition, d-penicillamine and colchicine are helpful.  Oxybutynin usually improves urinary incontinence, and sildenafil citrate has been shown to correct most cases of impotence; however, the alterations of sexual function are much more complicated, with loss of libido and especially low back and lower extremity pain during and after intercourse. Muscle relaxants are indicated if muscle spasms are severe and not susceptible to treatment with physical therapy and reconditioning.

Once the proliferative phase starts, any intervention may exacerbate the pain path mechanisms; therefore, invasive procedures have to be selected if the risk/benefit ratio is favorable. Epidural steroids are helpful in producing temporary pain relief and reducing the extradural formation of fibrosis; so is the epidural and intrathecal infusion of analgesics. SC stimulation reduces pain temporarily in localized (mononeuronal) cases. Neuroplasty is contraindicated because it requires the injection of 10% hypertonic saline and hyaluronidase that produces arachnoiditis.

The surgical breakdown of adhesions, even when performed meticulously under the microscope carries a great risk because SC dysfunction may be aggravated; laminectomies, foraminotomies and spinal fusions would need to be absolutely indicated because of the potential danger of recurrent dural sac injury and entry of blood. Long-term opioid therapy is not to be taken lightly, especially with Schedule II “slow-release” preparations; the consequences of drug dependency are intangible, but very real, with serious behavioral alterations.  Medications in Schedule III are preferred.

A variety of new therapeutic agents and interventional modalities are being proposed mostly for the symptomatic treatment of ARC; however, the most important therapy is prevention, since most of these cases are iatrogenically caused.  Education of physicians, nurses, and technicians regarding the numerous causes of this disease is an essential initial step, followed by the information to the public in general, and to patients with spinal disease in particular, so as to warn them against accepting questionably effective procedures in desperation to have their pain relieved and to procure competent and responsible physicians in their care.  Once an injurious event takes place, prompt action to define the precise diagnosis and to institute treatment is primordial. There is no place for hesitation since there is only a short window of opportunity during which chances to reverse the process are feasible. Once the proliferative phase begins, there is only symptomatic treatment.