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What is Arachnoiditis Ossificans & How is it Treated?

The meninges are the protective covering of the brain and spinal cord and consists three layers. The middle layer is called arachnoid. The chronic inflammation of arachnoid is called Arachnoiditis.1 It begins as adhesive arachnoiditis and ends as arachnoiditis ossificans. The later term was coined by Kaufman and Dunsmore in year 1971.

What is Arachnoiditis Ossificans?

Arachnoid inflammation may be caused due to infection of the spine or due to adverse reactions to chemicals. It can also be a result of direct injury to spine or complications from spinal surgery. This leads to formation of a scar tissue which compresses nerve roots and makes their ends sticky. This further prevents blood supply and the flow of cerebrospinal fluid (CSF), which leads to a painful condition called adhesive arachnoiditis. It is characterized by unremitting pain and disability. In advanced stages, the arachnoids become ossified leading to arachnoiditis ossificans.

What is Arachnoiditis Ossificans

Arachnoiditis ossificans is a rare medical disorder. It is characterized by the ossification (calcification) or bone formation of the arachnoid membrane of the thoracic and lumbar spines.2 In some cases, it can be treated with surgery.

Causes of Arachnoiditis Ossificans

The causes of arachnoiditis ossificans are similar to adhesive arachnoiditis and are as follows:

  • Chemically induced injury:
    • Spinal injections such as steroid injections in the subarachoid space. A steroid medicine called Depo-Medrol is often a cause of new cases of chemically-induced arachnoiditis.
    • Injection of myelogram dye (oil based contrast agents) during CT scan.
    • Spinal anesthesia.
    • Injectable drugs for cancer treatment.
  • Mechanically induced injury:
    • Spinal injury due to surgery.
    • Injury due to accident or a fall.
    • Chronic spinal stenosis.
    • Multiple lumbar punctures during spinal taps.
    • Spinal injections that are misplaced and delivered into the intrathecal region.
    • Arachnoid hemorrhage.
  • Infection:
    • Bacterial and viral infection leading to cerebral and spinal meningitis.
    • Tuberculosis and syphilis infection of the thoracic region of the spinal cord.

Symptoms of Arachnoiditis Ossificans

The symptoms of arachnoiditis ossificans resemble those associated with other spinal conditions including back pain, muscle spasms, pain, headache, dizziness and alterations of balance. Most of these arachnoiditis ossificans patients present with neurological deficits like inability to walk due to lower limb weakness, although some of them may be asymptomatic.3

Epidemiology of Arachnoiditis Ossificans

Arachnoiditis ossificans is uncommon in the population, hence it’s exact prevalence is not known. It is estimated that nearly 11,000 new cases of arachnoiditis are diagnosed in United States of America each year. However, the exact number of cases for arachnoiditis ossificans is not yet identified due to lack of proper data.

Prognosis of Arachnoiditis Ossificans

There is no best treatment available for arachnoiditis ossificans. If the symptoms of arachnoiditis ossificans are mild then the conservative treatment is helpful and the patient can become free from the extreme symptoms over a period of time. In patients with severe symptoms of arachnoiditis ossificans, it is treated with surgery. When multiple nerve roots are involved and even if intrathecal ossification is removed, the prognosis for arachnoiditis ossificans is yet poor.

Diagnosis of Arachnoiditis Ossificans

The doctor performs physical examination and takes a detailed medical history of the patient. This helps them to understand the extent and severity of arachnoiditis ossificans. The following tests are then recommended to evaluate further:

  • The main diagnosis is done by the means of Magnetic Resonance Imaging (MRI) to assess the contents of thecal sac, the clumping of the nerve roots and to differentiate the mass lesion which stimulates arachnoiditis ossificans. To confirm, a further CT scan must be performed to evaluate the full extension of the ossified mass.
  • The physical examination includes detecting changes in reflexes, sensory deficits and any alterations in balance.
  • Electromyogram (EMG) or Nerve conduction velocity (NCV) tests are used to examine the nerve damage.

Treatment of Arachnoiditis Ossificans

Currently there is no complete cure for arachnoiditis ossificans. It is managed by means of lessening of the pain by medication and physical therapies.

  • The treatment decisions for arachnoiditis ossificans are taken based on the location and morphology of the calcifications and in relation to compression of the spinal cord or nerve roots. Generally, decompressive laminectomies, anterior fusion, and foraminotomies procedures are recommended and have shown good results.
  • Only 50% of arachnoiditis ossificans patients managed with surgical intervention showed improvement. Surgery is not of much help when multiple nerve roots are involved even when the ossified mass is removed.


Arachidonitis ossificans is a rare medical condition. It has a debilitating effect on the quality of life of the person suffering from it. Since arachnoiditis ossificans is uncommon, hence not much research could be done to understand how to tackle this problem. If the symptoms of arachnoiditis ossificans are mild, conservative management is recommended. In patients with severe or deteriorating symptoms of arachnoiditis ossificans, surgery is often performed and even with surgical removal, the clinical outcome is generally poor.


Also Read:

Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:September 23, 2021

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