THE ADHESIVE ARACHNOIDITIS SYNDROME

INTRODUCTION

This article aims to give an overview of this complex and relatively uncommon condition, so that patients and their physicians have a clearer understanding, and can work together to combat the devastating effect it can have on people’s lives.

Arachnoiditis is a chronic, insidious condition that causes debilitating, intractable pain and a range of other neurological problems. It has been regarded as rare by the medical community, but Burton reported as early as 1978([1]) that it is “common in patients with severe back and/or leg pain and functional impairment due to the failed back surgery syndrome.”

Arachnoiditis is the third most common cause of Failed Back Surgery Syndrome (FBSS), after stenosis and recurrent disc problems. Arachnoiditis was previously the second most common cause. This was largely due to the adverse effects of oil-based myelography. The incidence has decreased, but a high proportion of cases of clinically significant adhesive arachnoiditis is now found to be due to the adverse effects of epidural steroids such as Depo-Medrol (Depo-Medrone).

THE SCALE OF THE PROBLEM

Adhesive arachnoiditis is not a notifiable disease and is significantly under-diagnosed. During the Proceedings of the British House of Commons, March 25th, 1998, the issue of arachnoiditis due to Myodil was raised. In answer to the question of the number of cases within the last 20 years, the Under-Secretary of State for Health replied “the information requested is not available” ([2]).

Burton ([3]) has attempted to suggest an estimated figure for cases in the U.S., using results of an international study that showed lumbo-sacral adhesive arachnoiditis to be responsible for about 11% of all Failed Back Surgery Syndrome cases. Tying this in with the number of surgeries performed in the last 50 years, and an average rate of 25% FBSS, he estimates “at least 1,000,000 FBSS cases in the U.S. would then have been causally and primarily due to the production of lumbo-sacral adhesive arachnoiditis. If one brings in the rest of the world the case estimate would have to be doubled.”

PATHOLOGY

In the first stage the spinal nerves are inflamed (radiculitis) and the adjacent blood vessels distended (hyperaemia). The subarachnoid space disappears. Deposition of collagen fibrils (scar tissue) begins. In the second stage, (arachnoiditis) the scar tissue increases, and the nerves become adherent to each other and the dura. The third stage, (adhesive arachnoiditis), involves complete encapsulation of the nerve roots. The subsequent compression causes them to atrophy. The scarring prevents the arachnoid from producing spinal fluid in that area. These stages were described by Burton in 1978.

In some cases, the scar tissue calcifies (arachnoiditis ossificans).

Benini and Blanco ([8]) described arachnoiditis as “cystic and adhesive in nature”. The cysts are collections of spinal fluid walled off by the meningeal adhesions. Arachnoid cysts are seen in some cases, especially if there is a foreign body present. They are particularly seen after Pantopaque myelography.

An animal study ([9]) showed that there was proliferation of fibrous tissue, lymphocyte infiltration and that the pial blood vessels were obliterated. In the spinal cord adjacent, there were multiple small areas of demyelination. Cavitation of the cord was observed in areas where there was ischaemia (poor blood supply). Syringomyelia (cavity) is a complication of arachnoiditis, probably arising due to the pressure dissociation between the subarachnoid space and the central canal. It must be stressed that it does not occur in all cases of arachnoiditis.

A further, uncommon, complication is communicating hydrocephalus. This is thought to be due to alterations in the cerebrospinal fluid dynamics, due to the effects of the scarring in the subarachnoid space.

Arachnoiditis may, in a minority of cases, involve the brain as well as the spinal cord.

There are also subdivisions of the condition called rhinosinugenic arachnoiditis and optochiasmic arachnoiditis, which are rare forms principally affecting the brain.