Arachnoiditis is chronic inflammation of the arachnoid, one of the three meninges that surround and protect the central nervous system.
Arachnoiditis is defined as chronic inflammation of the arachnoid, one of the three meninges. The arachnoid has the appearance of a spider-web-like layer, and it lies between the other two meningeal membranes, the dura mater (the outermost membrane) and the pia mater (the deepest membrane). Together with the classical role of protection, the arachnoid has the additional function of containing the cerebrospinal fluid, and it acts as an elastic absorber and a physiological filter for the cerebrospinal fluid as it passes from the subarachnoid space into the venous sinuses. Depending on the situation, arachnoiditis can have severe consequences, which include movement and other neurological disorders. Although arachnoiditis is now regarded as a rare disease, back in 1978 Charles V. Burton  defined it as common when he noted that it is often found in cases of functional impairment due to failed back surgery syndrome. Among these patients, arachnoiditis now represents the third most common pathological condition, after stenosis and recurrent disc complications.
Initially, arachnoiditis was recognized in cases of post-spinal surgery complications, and it was long assumed to be a surgery-induced problem. Broadly speaking, there are three types of arachnoiditis, which depend on the cause of the inflammation. The first type includes all cases of arachnoiditis due to mechanical stress, such as trauma    and the already mentioned surgical difficulties   . The second type includes the cases of irritation by foreign substances, particularly like old radiographic contrast agents that were widely used for myelography in Europe and North America up to the 1980s . The third and last type of arachnoiditis includes all of the cases of arachnoiditis that are triggered by infectious diseases of the spinal cord, such as pyogenic infection  , tuberculosis  and leutic meningitis .
Arachnoiditis is considered a rare disease by the National Institutes of Health. It may develop in patients who have undergone spinal surgery and intrathecal injections of toxic fluids, or who have suffered head and/or spine injuries. Arachnoiditis tends to be more frequent in females than males, which appears to be due to the spinal or epidural anesthesia that pregnant women receive during delivery. Many cases of arachnoiditis go misdiagnosed or undiagnosed for different reasons, which makes it extremely difficult to determine its precise prevalence and incidence. Burton attempted to estimate these figures for lumbo-sacral arachnoiditis in an online article in 1997 , where he indicated that there have been at least one million cases over the last few decades in the USA alone. If this estimate can be proven correct, the people suffering worldwide from some type of arachnoiditis must be of the order of at least tens of millions.
Arachnoiditis shows an initial inflammation phase that lasts around two months. This phase is usually characterized by the appearance of scarring, fibrosis and adhesion, together with nerve swelling and vasodilatation, as happens in other organs and tissues. If this is not treated, these changes can become permanent , and the inflammation can continue into the chronic proliferative phase. The appearance of profound structural alterations to the nerve roots in the anterior half of the dural sac can be typical of the first phase, whereby these nerve roots appear “enhanced” during the inflammation; these can then become “clumped” during the later chronic proliferative stage  . The condition can further degenerate with the formation of permanent scar tissue along with the adhesions that cause the nerves to stick together in intricate patterns. This pathological condition is known as chronic adhesive arachnoiditis, and it represents the end of the inflammatory stage, and is particularly painful for patients. If the inflammation is serious enough, arachnoiditis can begin to interfere with the functioning of the surrounding nerves, which can cause complications for the lower body parts, such as loss of full limb control.
Arachnoiditis remains an incurable disease that causes chronic pain and neurological deficits, and that shows little or no significant improvement with treatment. The general outlook for the patient is complicated by the absence of any specifically predictable progression pattern and the apparent lack of correlation between the beginning of the illness and the start of the symptoms (as it can take many years for the disease to be manifest). The prognosis for patients with arachnoiditis is still very poorly defined and the relevant literature is not sufficient. A book by Guyerin 1989 appears to have been the most cited study to date, in which he contends that, on average, arachnoiditis shortens life expectancy by as much as 12 years. There has been deep controversy over the question of whether or not arachnoiditis has a progressive nature. Many patients show increasing pain levels and loss of function over a period of many years, while other patients appear to remain stable after reaching a plateau. Rapid decline has only been observed in cases of injury from violent incidents, like car accidents. Indeed, the majority of patients who have suffered arachnoiditis for up to 20 years still remain in reasonably good condition, and relatively independent.
Other complications can appear during the disease progression, like arachnoid cysts, syringomyelia, and hydrocephalus, all of which are usually coupled to depression and osteoporosis (due to the lack of mobility). Unrelieved pain and the consequent depression can in turn lead to despair and suicide, indirectly making arachnoiditis a fatal disease.
Although there is no consistent pattern, the symptoms of arachnoiditis mostly involve the nerves between the lower back and the legs, and they tend to become more severe and permanent as the illness progresses. The predominant symptom is undoubtedly the chronic and unrelenting pain, which occurs mainly in the limbs and, as indicated, the lower back, although it can spread up the spine and down the arms in the later pathological phases. Numbness is also a major symptom, and can often involve other body parts, which can become extremely sensitive to touch. Among other frequent symptoms there are muscle complications such as cramps, twitches and stiffness, together with neurological disorders that affect the bladder, bowel, and sexual functions. The less frequent, but nevertheless particularly insidious, problems can include depression, difficulty in thinking clearly, and sleep disturbance, all due to the constant chronic pain.
The diagnostic procedure of choice to identify arachnoiditis is magnetic resonance imaging (MRI). Where MRI is contraindicated, computed tomography myelography appears to be a valid alternative, although the images provided do not have the same quality as those for MRI, and thus they are not as informative. In both cases, the main pathophysiological features observed are subarachnoid space narrowing or blockage, nerve root thickening, and lack of nerve root sleeve filling. Physical examination of the patient should be added to these classical imaging findings, to determine their physiological alterations, such as for sensory deficit, reflexes, and weakness. As the symptoms of arachnoiditis vary greatly, and sometimes appear in relatively confusing combinations, this condition is often mixed up with simple irritation or compression of a single nerve.
Unfortunately, there is no cure for arachnoiditis. Treatment is difficult and mostly based on relieving the pain and improving the symptoms that negatively affect the daily routine of the patient. The options are thus those that are usually chosen to cope with other chronic pain conditions, such as non-steroidal anti-inflammatory drugs, or narcotic pain relievers, together with a general program of pain management and psychotherapy. As steroid injections have been reported to cause and at least to worsen arachnoid inflammation, their use is generally discouraged by the medical community. Surgery is also strongly discouraged, as it can only cause further development of scar tissue and the outcomes are frequently poor and short-lasting.
The prevention of arachnoiditis mainly consists in preventing post-surgical complications. Many guidelines have been published in this regard which underline a series of measures and surgical principles such as scar prevention or the necessity of gently handling tissues while performing surgical procedures. A good physician should know these measures and keep updated with the new versions of specific guidelines, to minimize the risk of possible port-operative complications.
Arachnoiditis is inflammation of the arachnoid, which is the central membrane of the three meninges that surround and protect the central nervous system (i.e., the brain and spinal cord). The causes of arachnoiditis are the same mechanical, chemical and biological stimuli that usually trigger inflammation, which here include trauma and surgically related complications, chemical irritants, and pathogens that attack the spinal cord. The symptoms of arachnoiditis mostly involve the nerves between the lower back and the limbs, and they are normally manifest as intense chronic pain, numbness, muscle complications, and neurological disorders that affect the bladder, bowel, and sexual functions. There is no cure for arachnoiditis, and treatment of the patients with arachnoiditis is limited to the relief and improvement of their symptoms through conveniently organized pain-management programs.