The Aword

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Arachnoiditis or Epidural Fibrosis

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A frequent question arises about the difference between these two terms.

Arachnoiditis is chronic inflammation inside the dura, in the arachnoid layer of the meninges (see below) whereas epidural (also called peridural, extradural) fibrosis is scarring outside the dural sac.

This latter may also be referred to as "adhesions" or "scar tissue".

Many doctors appear to regard epidural fibrosis as less clinically significant than arachnoiditis, but in essence the nerve root compression arising from epidural fibrosis may cause similar clinical problems in terms of lower limb pain, sensory disturbance and weakness.

Epidural fibrosis differs from arachnoiditis in that it is more likely to be a localised problem - affecting just one or two nerve roots - and is generally a post-surgical phenomenon, although it may also be a sequela to invasive procedures such as chemonucleolysis.

In cases of arachnoiditis, there is often associated epidural fibrosis, but the reverse is not generally acknowledged, so that patients may be left with a diagnosis of epidural fibrosis and are unable to obtain a diagnosis of arachnoiditis even when the clinical picture fits.

Arachnoiditis is an underdiagnosed condition.