Arachnoiditis: Definition and Causes
Arachnoiditis is a chronic inflammatory condition affecting the arachnoid mater (one of the protective membranes covering the brain and spinal cord) and subarachnoid space, characterized by adhesion formation, scarring, and fibrosis that can lead to severe neurological dysfunction.
Definition and Clinical Presentation
Arachnoiditis primarily affects the spinal cord and nerve roots, causing:
- Severe back pain, particularly in the lumbosacral region
- Paresthesia and numbness not following typical dermatome patterns
- Progressive weakness of lower extremities (paraparesis)
- Bladder, bowel, and/or sexual dysfunction
- In severe cases, patients may become wheelchair-bound 1, 2
The condition is characterized pathologically by inflammation of the pia mater of the spinal cord and nerve roots, leading to adhesions, scarring, and eventual entrapment of neural elements 2.
Major Causes of Arachnoiditis
Arachnoiditis can be categorized into three major etiological groups 2:
1. Infectious Causes
- Neurocysticercosis: Subarachnoid cysts from Taenia solium infection can manifest as acute or chronic eosinophilic meningitis leading to arachnoiditis 3
- Tuberculosis: Tuberculous meningitis can lead to chronic arachnoiditis
- Fungal infections: Including coccidioidomycosis and paracoccidioidomycosis 3
2. Chemical/Toxic Causes
- Myelographic contrast agents: Particularly oil-based dyes 4
- Antiseptics: Chlorhexidine contamination during central neuraxial blockade procedures 3
- Intrathecal medications: Including certain antibiotics, chemotherapeutics, and even therapeutic substances like nusinersen 5
- Preservatives in medications: Particularly in epidural steroid injections
3. Mechanical/Traumatic Causes
- Spinal surgery: A common iatrogenic cause 1, 4
- Epidural anesthesia and spinal procedures: Traumatic punctures or contamination during procedures 4
- Blood in the intrathecal space: From traumatic taps or hemorrhage 4
- Direct trauma to the spinal cord or nerve roots: During medical procedures 4
4. Other/Rare Causes
- Familial forms: Rare genetic predisposition has been reported 6
- Idiopathic cases: Some cases have no identifiable cause 2
Diagnostic Approach
Magnetic Resonance Imaging (MRI) is the most sensitive and specific diagnostic tool for arachnoiditis 1, 2. Characteristic findings include:
- Clumping of nerve roots
- Dural sac deformities
- Loculation of the subarachnoid space
- Associated syringomyelia in advanced cases
Clinical Implications
The condition can be severely debilitating, with many patients experiencing progressive neurological deterioration. Complications may include:
- Development of syringomyelia
- Permanent neurological deficits
- Chronic pain syndromes
- Loss of mobility and independence
Prevention Strategies
Prevention is critical, especially in medical settings:
- Meticulous antiseptic technique during neuraxial procedures
- Using 0.5% chlorhexidine in alcohol (rather than 2%) for skin antisepsis before central neuraxial blockade 3
- Avoiding introduction of blood, antiseptics, or other potential irritants into the subarachnoid space
- Careful monitoring of patients receiving intrathecal therapies 5
- Prompt treatment of CNS infections that could lead to arachnoiditis
Early recognition and intervention are essential to prevent progression to irreversible neurological damage, though treatment options remain limited once the condition is established.