Arachnoiditis is a persistent inflammation of the arachnoid mater as well as subarachnoid space due to many possible causes such as prior spinal surgery, infection, subarachnoid hemorrhage, lumbar epidural injections, oil-based myelographic contrast agents, chemical irritation or idiopathic. This condition involves membrane thickening, dural adhesions, scar tissue formation, and clumping of nerve roots. As the disease progresses, scar tissue can encapsulate the nerve roots, impede CSF flow, and lead to a condition called chronic adhesive arachnoiditis. Another late-stage complication called arachnoiditis ossificans can also occur when the arachnoid mater becomes ossified due to prolonged inflammation, resulting in progressive neurological debility. Spinal cord swelling and syringomyelia formation can also be a manifestation of advanced arachnoiditis.
The exact causes of arachnoiditis are often not known since it is a rare condition with multiple possible causes, highly variable time from possible insult until clinical manifestations appear, and variable findings on imaging which delays or complicates making the diagnosis. Purported causal factors can be divided into three general categories- chemical, mechanical, and infectious. Possible chemical causes include various types of intentional or unintentional injections into the subarachnoid or subdural space where injectates may contain various possibly neurotoxic substances such as sulfite-containing preservatives, blood, other contaminants, or direct local anesthetic toxicity. Mechanical causes may include accidental trauma or surgical interventions. Possible infectious causes include various bacterial or viral infections such as tuberculosis and HIV. In a study of 50 patients with arachnoiditis, it was noted that 90% of these patients had a previous history of the intervertebral disease, Iofendylate myelography, and lumbar spine surgery. Various causative factors have been suggested through case reports over the past 50 years, where previous trauma, spinal surgery, and subarachnoid hemorrhage are among the most frequently reported causes. Other commonly-listed possible causes include CNS infections, contrast myelography, spinal anesthetic agents, accidental chemical injection, and disc herniations. Less commonly reported causes include ankylosing spondylitis, Guillain-Barré syndrome, autoimmune vasculitis as well as idiopathic. Above mentioned causes precipitate scar tissue encapsulation of nerve roots, impaired blood supply, starvation of oxygen and nutrients and accumulation of waste products, frequently resulting in pain and neurological deficits.
There is no well-defined epidemiology in regards to arachnoiditis. Since Horsley described it in 1909 as a disease entity, fewer in 1000 case reports exist in the literature. Its true incidence or frequency is hard to determine as it is a rare, difficult-to-diagnose condition with many different terms used in the literature to describe it, such as “chronic spinal meningitis” and “meningitis serosa circumscripta spinalis.” Since the clinical presentation of arachnoiditis ranges from sub-clinical to severe, many of the mild or subclinical cases of arachnoiditis will either never be diagnosed or not reported. Therefore the true frequency of arachnoiditis remains not only unknown but also likely significantly underestimated. It was noted recently, though, that the frequency of lumbar arachnoiditis appears to be increasing due to an increasing amount of lumbar spine surgeries.
Various purported chemical, mechanical, and infectious insults involve injury to and inflammation of the subarachnoid or subdural space. These possible causes include trauma, surgery, infection, ankylosing spondylitis, Guillain-barre syndrome, autoimmune vasculitis, and neurotoxic substances such as sulfite-containing preservatives, myelographic agents, blood, other contaminants, or local anesthetics. The injury to and inflammation of the subarachnoid or subdural space precipitate collagen deposits, scar tissue encapsulation of nerve roots, fibrosis, decreased CSF flow, clumping of nerve roots, impaired blood supply, starvation of oxygen and nutrients and accumulation of waste products, nerve atrophy, nerve damage, and possibly tethered nerves. Arachnoiditis frequently results in pain and possible neurological deficits.
The clinical presentation of arachnoiditis is variable. Arachnoiditis often presents as a chronic, painful, and debilitating condition with an insidious onset. There is a variable, inconsistent time frame between a possible inciting event or events and the onset of symptoms. For example, it was reported the average time between the rupture of an aneurysm, and the spinal adhesive arachnoiditis was 10 months with a highly variable course described as static and progressive. Arachnoiditis also displays a variable severity of symptoms ranging from subclinical to advanced and severe. If the arachnoiditis is severe, the clinical presentation can be involvement of both the spinal cord and connecting nerve roots, often resulting in severe back pain, numbness, and tingling of the extremities, myeloradiculopathy symptoms of the lower limb, impairment of bowel, bladder, sexual functioning, difficulty sitting for long, as well as difficulties controlling limbs if an efferent motor nerve root is affected. The most common clinical presentation is that of back pain gradually followed by radicular pain and then sensory defect. Less common symptoms may involve weakness, gait imbalance, as well as possible neurogenic bowel or bladder. Urinary symptoms develop late in 23% of arachnoiditis patients and are often characterized as urgency, increased frequency, and less commonly, incontinence. Paraplegia, as well as isolated low back pain, have also been documented. Clinical symptoms vary according to the affecting spine levels and severity of the arachnoiditis. The involvement of lumbar and thoracic spine is the most common, followed by lumbosacral, with entire spine involvement being the least common.
There is no reliable laboratory test, or consistent electromyography findings can be used to diagnose arachnoiditis formally. The diagnosis is based on clinical presentation and symptoms, along with supporting MRI or CT myelography. Pathological radiologic features do not always correspond to clinical findings and their severity. The diagnosis of adhesive arachnoiditis should start by taking a thorough history to identify possible associated causes and risk factors. It is important to exclude other possible treatable conditions responsible for the symptoms. The MRI scan remains the imaging modality of choice. However, in conditions where MRI was negative, thecaloscopy can also be used to help diagnose loculated arachnoid cysts for the diagnosis of arachnoiditis. It is worth noting that neurophysiological tests such as EMG and NCV, are not useful to make a reliable diagnosis of arachnoiditis, especially in the later stages of arachnoiditis. The diagnosis of arachnoiditis is often made clinically based on presentation including typical clinical symptoms, exam findings, clinical history of possible inciting events, and subsequently corroborated by imaging findings consistent with arachnoiditis. For the diagnosis of chronic adhesive arachnoiditis, MRI has a high sensitivity of 92%, high specificity of 100% as well as high accuracy of 99%. Most frequent MRI findings are loculated arachnoid cysts involving several vertebral bodies or possibly the entire spine with a reported frequency of 79%. Other common MRI findings include spinal cord swelling with or without increased T2 signal, cord displacement, cord atrophy, nerve root clumping, syrinx formation, and arachnoid septations. Typical findings on CT myelography are myelography spread block, thickened or tethered nerve roots, soft tissue mass within the arachnoid space, as well as intrathecal calcification. For adhesive arachnoiditis, MRI is a better modality because it can differentiate between benign meningeal calcification from frank ossification of the arachnoid tissue. Non-contrast enhanced computed tomography CT, however, offers more sensitivity than MRI for the diagnosis of arachnoiditis ossificans specifically. Spinal cord biopsy is sometimes indicated to exclude the presence of tumors when cord swelling and an intramedullary increased signal is present.
Arachnoiditis is an incurable disease that is challenging to treat. The treatment of this condition focuses mainly on alleviating pain, improving quality of life, and managing symptoms. It is essential to help these patients cope with their pain and any functional limitations with which they may struggle. Multimodal and interprofessional pain management is recommended. Medication management may include NSAIDs, opioids, and various adjuncts such as duloxetine, gabapentin, pregabalin, and muscle relaxants such as baclofen. Other important treatments include physical therapy as well as cognitive behavioral therapy, biofeedback, imagery, and possibly other forms of psychotherapy and support. Additional treatment modalities may include thecaloscopy and neurostimulation. Intrathecal therapy has also been used, albeit with some potential risk of worsening the arachnoiditis. The role of surgical treatment remains unclear, but when used, surgical treatments usually involve releasing a tethered cord and restoring CSF flow. Reported surgical interventions include shunt, cyst fenestration, myelotomy, duralplasty, lysis of adhesions, and laminectomy. Long term prognosis after surgery remains poor with immediate improvement, often followed by relapse and progressively worsening symptoms. Though surgery can provide temporary relief such as decompressor resection of isolated ossified plaques in arachnoiditis ossificans, it has a poor outcome overall. For advanced chronic adhesive arachnoiditis with obstruction of CSF flow, various treatment options are present to restore flow continuity, though with a high rate of recurrence and limited success. The only condition that might benefit from early surgical intervention is the local reduction of epidural infection as it provides the benefit of preventing inflammation passing through dural sac and subsequent severe adhesive arachnoiditis. Epidural steroid injections are generally not recommended due to concerns that these injections could potentially exacerbate the arachnoiditis condition since various injectates have been suggested to possibly cause arachnoiditis. There are, however, isolated reports of pain improvement after epidural steroid injections. Oral corticosteroid so far has not shown therapeutic benefit. Since most patients with arachnoiditis have difficulty sitting due to the pain, some patients may have significant benefits (improved quality of life and mobility) from motorized assistant devices such as standing wheelchairs, although standing acceptance and vibration endurance should be evaluated before proceeding.
The differential diagnosis includes various conditions such as spinal cord tumors, disc herniations, postlaminectomy pain syndrome, multiple sclerosis, cauda equina syndrome, syringomyelia, and infections such as an epidural abscess epidural hematoma or a central nervous system infection.
Unfortunately, this condition is usually chronic and may be progressive in some individuals. Supportive care and management of the chronic symptoms is the mainstay treatment for most patients. The quality of life of severely-affected patients is often very compromised due to significant neurological symptoms and pain. Individuals diagnosed with this condition may be disabled and unable to work full time due to constant pain and various neurological deficits. Many patients with arachnoiditis, however, can walk and drive a car without significant limitations. The course of this disease remains highly variable due to the fact that arachnoiditis is both a static and progressive disease. It has been observed that most patients with arachnoiditis had relatively stable functional disability without significant exacerbations and no improvement in symptoms from the time of diagnosis. However, the severity of symptoms can fluctuate. The natural course of the disease is that neurologic deficits do not typically progress as much as surgical interventions can cause symptoms to progress. Although arachnoiditis is a chronic disabling disease, it is not usually a life-threatening condition itself. The natural course of the disease is not a progression of symptoms and functional impairments that results in death. Rather, it is the effect of chronic, accumulating pain as well as functional limitations, diminished quality of life, and a variety of secondary problems that typically brings detrimental results. A long-term follow-up study of fifty patients revealed death by suicide in two patients as well as other deaths not directly related to arachnoiditis, thereby shortening the average lifespan by 12 years.
Most of the purported causes of arachnoiditis appear to be iatrogenic. It is, therefore, important to recognize that arachnoiditis is a rare but possible complication of various treatments, including surgery and injections. The iatrogenic aspect of the cause of arachnoiditis should be considered and brought to a patient's attention when discussing the risks and benefits of an invasive spinal procedure or surgery. For instance, up to 90% of arachnoiditis has been linked to lumbar spine surgery. It is a common and current medical practice to deliver various medications in or near the spinal fluid space, such as steroids, local anesthetics, contrast agents, and chemotherapeutic agents. Although the true risk of arachnoiditis remains unknown and appears to be low, the possibility of this type of neurologic injury should be recognized and considered when assessing the potentials benefits and risks of invasive spinal procedures, surgery, or injections.
To better understand arachnoiditis, it is important to increase the awareness of, the recognition of, and the reporting of this condition by various healthcare professionals. If more subclinical cases of arachnoiditis or mild cases arachnoiditis are reported, it will help better identify the true frequency of this potentially debilitating condition and allow a better understanding of the various causes of arachnoiditis. More standardized and well-defined pathognomonic findings for arachnoiditis on imaging will be very important for making a timely and accurate diagnosis as well as important for avoiding unnecessary interventions, especially surgical interventions, which may exacerbate the condition. For instance, it is important to differentiate tumors from arachnoiditis since the appearance of interstitial edema, and cord swelling can mimic each other. An improved understanding of arachnoiditis and its exact causes will help medical professionals prevent it from occurring in patients, thereby improving outcomes.
It is crucial to raise medical awareness of the potential causes of arachnoiditis, especially iatrogenic potential causes such as spinal surgery, contrast pyelogram, and spinal injections. Given that many of the purported causes of arachnoiditis are iatrogenic, health care professionals need to consider the risks and benefits of an invasive spinal procedure, injection, or surgery and discuss this as a potential risk with patients.
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