Arachnoiditis is a chronic inflammatory disorder affecting the arachnoid mater. This condition involves the formation of scar tissue, or adhesions, within the subarachnoid space that can bind and compress the spinal nerves. Because the resulting symptoms of nerve dysfunction are often non-specific and overlap with many other spinal conditions, establishing a diagnosis is a complex process. The identification of arachnoiditis requires a careful, multi-step investigation that combines a detailed patient history, thorough physical examination, and specific advanced imaging studies.
Initial Clinical Evaluation
The diagnostic process begins with a comprehensive review of the patient’s medical history to identify potential triggering events. Arachnoiditis is often associated with a history of spinal trauma, previous spinal surgeries, or procedures involving injections into the spinal canal, such as epidural steroid injections or certain types of myelograms performed decades ago.
A physical and neurological examination follows the patient interview to assess the pattern of nerve involvement. Patients frequently report chronic pain in the lower back, legs, or buttocks, often described as burning, shooting, or electric-shock sensations. The examination may reveal sensory defects, such as numbness or tingling, motor weakness, or altered reflexes that can help localize the affected nerve roots. Although these symptoms are not unique to arachnoiditis, their specific combination and progression can raise a physician’s suspicion of this particular inflammatory condition.
Essential Imaging Procedures
Imaging studies are required to visualize the structural changes in the spinal canal that are characteristic of arachnoiditis. Magnetic Resonance Imaging (MRI) is considered the preferred imaging method, as it offers high sensitivity for visualizing the soft tissues of the spinal cord and nerve roots. The MRI allows physicians to look for specific findings that represent the inflammatory scarring process within the spinal fluid space.
One of the most common signs of arachnoiditis on an MRI is the clumping of nerve roots. In more advanced cases, the nerve roots may adhere to the inner lining of the thecal sac, creating the appearance of an “empty” sac with no visible nerves floating freely in the spinal fluid. In the most severe instances, the entire collection of nerve roots can be matted together into a single, centralized soft tissue mass.
Computed Tomography (CT) Myelography is an alternative or confirmatory test used when MRI results are inconclusive or when a patient cannot undergo an MRI due to a medical device like a pacemaker or spinal hardware. This procedure involves injecting a contrast dye into the subarachnoid space via a lumbar puncture before performing the CT scan. The contrast dye highlights the space and its contents, revealing characteristic features such as thickened, tethered nerve roots or a blockage of the flow of spinal fluid. CT myelography can also be particularly useful for identifying the presence of intrathecal calcification or ossification that may be missed by a standard MRI.
Functional Nerve Testing
Functional nerve testing is often employed to assess the physiological impact of the inflammation and scarring on the nervous system. Electromyography (EMG) and Nerve Conduction Studies (NCS) are the two primary tests used for this purpose.
The NCS component involves applying small electrical impulses to the skin over a nerve to evaluate how quickly and strongly the nerve transmits signals. The EMG component uses a fine needle electrode inserted into various muscles to record the electrical activity, which can show signs of nerve damage in the surrounding tissue. Although these tests do not provide a specific diagnostic pattern unique to arachnoiditis, they can indicate the severity and location of chronic nerve root damage or polyradiculopathy. The results help to correlate the structural abnormalities seen on the MRI with the patient’s reported symptoms of pain, weakness, and sensory loss.
Ruling Out Other Conditions
A significant hurdle in diagnosing arachnoiditis is the overlap of its clinical presentation with several other spinal conditions, making it a diagnosis of exclusion in many cases. The process of differential diagnosis requires systematically investigating and eliminating other, more common causes of similar pain and neurological deficits. Physicians must consider conditions such as spinal stenosis or degenerative disc disease.
Other conditions that can mimic the diffuse, chronic pain and nerve symptoms of arachnoiditis include complex regional pain syndrome, peripheral neuropathy, and post-laminectomy pain syndrome, sometimes called Failed Back Surgery Syndrome. The detailed history, imaging evidence of nerve root clumping, and functional test results must all point toward the inflammatory and adhesive process of arachnoiditis once these other possibilities have been thoroughly investigated and discounted. The final diagnosis is ultimately clinical, relying on the combination of a consistent medical history, characteristic imaging findings, and a neurological examination that cannot be explained by any other single condition.