Myelograms are a diagnostic tool used before spinal surgery. A contrast medium or dye injected into the spinal canal space trickles into and around the discs and nerve roots to show up any problems under X-ray.

Critics fear the dye may cause spinal arachnoiditis, and suggest MRI (magnetic resonance imaging) or a CT (computed tomography) scan as a safer alternative.

Before the controversy, nearly a half-million myelograms were being performed in the US every year.

Arachnoiditis is a little-understood condition in which the middle membrane surrounding the spinal cord becomes inflamed and scarred. The dense scar tissue then presses constantly on the nerve. Symptoms can mimic other conditions such as spinal cord tumours, cauda equina syndrome, arachnoiditis ossificans and syringomyelia (Orthop Nurs, 2003; 22: 215).

For most sufferers, arachnoiditis is a disabling disease with severe pain and neurological problems. As it progresses, some symptoms become permanent.

Orthopaedic surgeon Dr Charles Burton, of the Institute for Low Back Care in Minneapolis, estimates that a million people worldwide have myelogram-induced arachnoiditis, specifically caused by the oil-based dye iodophenylundecylic acid (Pantopaque) used in the tests.

This idea finds support in a study which found that a powder contaminant from surgical gloves could infect the myelogram needle and cause arachnoiditis (Am J Roentgenol, 1982; 138: 705-8). In animals, iodophenylundecylic acid combined with surgical glove powder caused mild-to-severe arachnoiditis in 10 of the 17 rabbits injected (Am J Neuroradiol, 1982; 3: 121-5).

Unfortunately, the introduction of water-soluble contrast media instead of oil-based dyes has not solved the problem. Arachnoiditis developed in 11 per cent of patients with methiodal sodium, 25 per cent of patients with iothalamate meglumine and 58 per cent of patients with iocarmate meglumine compared with 70 per cent with iodophenylundecylic acid (Br J Radiol, 1978; 51: 321-7).

A new contrast media, metrizamide (Amipaque), has proved to be the safest of all myelography dyes so far, but even this can still cause neurological complications. Seven of 75 patients given metrizamide for lumbar myelography developed a profound psychosis due to organic dysfunction, and three suffered from visual illusions or hallucinations.

Such disturbances have also been seen after myelography using other water-soluble contrast media (Neuroradiology, 1980; 19: 153-7).

Despite the dangers of using iodophenylundecylic acid for myelography, it continues to be used around the world, and some doctors maintain that it is safe. Furthermore, neither the US Food and Drug Administration (FDA) nor the British government has made any move to ban these oil-based dyes.
Megan McAuliffe