Arachnoiditis is a chronic inflammatory disorder affecting the arachnoid mater, one of the three membranes protecting the spinal cord and its nerves. This inflammation leads to progressive scarring and the formation of adhesions, often called chronic adhesive arachnoiditis. The resulting scar tissue causes spinal nerve roots to clump together or stick to the spinal canal lining, leading to severe, persistent pain and neurological deficits. Diagnosis is challenging because symptoms, typically severe back and leg pain, overlap significantly with many other chronic spinal disorders. A multi-step diagnostic process is required to confirm the characteristic scarring and exclude other potential causes.
Initial Clinical Evaluation and Symptom Mapping
The diagnostic process begins with a comprehensive evaluation of the patient’s medical history and current symptoms. The physician inquires about preceding events known as risk factors for arachnoiditis. These include prior spinal surgeries, significant spinal trauma, infectious processes like meningitis, or specific spinal procedures such as epidural injections or myelography.
A detailed patient history helps establish a timeline linking the onset of chronic pain to a potential inflammatory trigger, which is a key piece of the clinical picture. Symptoms are often mapped to identify patterns of pain, numbness, and weakness, which frequently involve the lower back and legs. Patients commonly report a severe, burning sensation, often described as relentless, which may be accompanied by muscle spasms or odd sensations like tingling.
A physical examination follows to assess the functional status of the nerves and spinal cord. The physician tests reflexes, sensory responses, and motor function to map specific areas of nerve damage or irritation. Weakness, gait imbalance, and neurogenic issues affecting the bowel or bladder are noted, as they indicate more severe nerve involvement. This initial evaluation establishes a clinical picture correlated later with advanced imaging findings.
Advanced Imaging
Imaging provides visual confirmation of the anatomical changes characteristic of arachnoiditis. Magnetic Resonance Imaging (MRI) is the gold standard for evaluation due to its superior ability to visualize soft tissues, including the spinal cord, nerve roots, and the arachnoid membrane. MRI findings must show specific patterns of scarring in the lumbar region, where the cauda equina nerve roots reside.
One common finding is the clumping or adherence of nerve roots, where the individual nerve fibers stick together and are displaced. This clumping may appear in the center of the thecal sac as a single soft tissue mass, sometimes called the “pseudocord” sign. Alternatively, the nerve roots can adhere to the periphery of the dural sac, resulting in an “empty thecal sac” appearance on axial images. Mild cases may show a loss of the normal “fanning” pattern of the nerve roots on sagittal views.
A Computed Tomography Myelogram (CT Myelogram) is often used if a patient cannot undergo an MRI, such as those with metal implants, or if MRI results are inconclusive. This procedure involves injecting a contrast dye directly into the space surrounding the spinal cord and nerve roots. The contrast dye illuminates the subarachnoid space and any irregularities caused by scarring.
Diagnostic findings on a CT Myelogram include irregularity or obstruction of contrast flow caused by adhesions, appearing as a partial or complete block. The nerve roots may appear thickened, tethered, or clumped together since the contrast material cannot flow freely around them. While MRI is preferred for soft tissue visualization, CT Myelogram is more sensitive for detecting arachnoiditis ossificans, a severe late-stage complication where scar tissue has turned to bone.
Differentiating Arachnoiditis from Other Conditions
The diagnosis of arachnoiditis is often one of exclusion because symptoms mimic several other spine-related conditions. Physicians must rule out other potential causes of chronic back and leg pain, such as severe spinal stenosis, chronic disc disease, or peripheral neuropathy. This process ensures the patient’s symptoms are correctly attributed to the inflammation and scarring of the arachnoid membrane.
To support this differential diagnosis, physicians may order specialized tests like Electromyography (EMG) and Nerve Conduction Studies (NCS). While these tests are not diagnostic for arachnoiditis itself, they are useful for assessing the extent and type of nerve damage. EMG and NCS can help determine if the problem originates in the nerve roots (radiculopathy), the peripheral nerves, or the muscles, helping to exclude other conditions.
Further laboratory testing, including blood work or analysis of cerebrospinal fluid, may be necessary to rule out active infectious or inflammatory causes. Excluding conditions like autoimmune disorders or infectious meningitis strengthens the case for arachnoiditis. The definitive diagnosis is reached through the clinical correlation of the patient’s history and neurological deficits with the characteristic imaging findings.