Arachnoiditis is an inflammatory disorder affecting the dura (exterior) and the arachnoid (interior) mater of the brain, the two of the three membranes (meninges) that cover and protect the brain, the spinal cord, and the nerve roots. The subarachnoid space contains the cerebrospinal fluid which circulates from the brain and spinal cord.
Inflammation of the arachnoid mater, when persistent can cause scarring and fibrosis, leading to abnormal adhesion of nerve roots to the dural sac or to each other. This results in a range of symptoms, such as neurological deficits and severe chronic neuropathic pain. Historically, tuberculosis and syphilis were common causes of myelitis and arachnoiditis. But due to effective treatment available, arachnoiditis is now rarely a complication of such infections. It is now often associated with fungal meningitis resulting from attempted epidural injections of tainted steroids.
The severity of the symptoms usually depends on the extent and location of the inflammation. If there is a direct injury to the spinal cord or to the nerve roots, it results in immediate, severe pain in the corresponding area of innervation. Chronic severe pain is typically localized in the lower back, perineum, legs, and feet; it may appear weeks after the inciting event (such as an invasive procedure). It mostly results in severe pain, accompanied by tingling or burning on the legs and feet, along with paresthesias. There may also be muscle cramps, gait abnormalities and alterations of proprioception. In some cases, there may be severe headaches, vision disturbances, hearing problems, dizziness, and nausea. Some patients report bowel, bladder, and sexual dysfunction.
In addition to introducing pathogens to the subarachnoid space, other ways an invasive spinal procedure can cause arachnoiditis include spinal cord damage resulting in myelomalacia or elongation of the nerve roots as they adhere to the dural sac wall. Development of arachnoid cysts and syringomyelia are also implicated in its pathophysiology.
The diagnosis of arachnoiditis is based on history of an invasive procedure or serious illness within the spine, signs of which may be observed on the physical exam. The diagnosis is confirmed on MRI with contrast, which is also excellent for the determination of the extent of the condition. If an MRI is contraindicated (presence of metal implants), the diagnosis of arachnoiditis will have to be made using a contrast-enhanced computed tomography (CT) scan. But an intrathecal injection of the contrast for a myelogram is problematic is an acutely inflamed spine.
Treatment is mainly symptomatic as there is no definitive cure for arachnoiditis. Painkillers are indicated but should be given with caution keeping the chronicity of the condition and the perils of long-term prescription (addiction i.e.). Mild physical therapy is recommended for affected individuals to restore and preserve function, including massage, mild exercise, hydrotherapy, and hot or cold compresses. Psychotherapy may be helpful if there is a concern for depression. Surgery is not indicated given the presence of scar tissue and fibrosis formation in the spine.