Recent reports from the Food and Drug Administration indicate that the arthritis drugs Remicade and Enbrel may cause in some patients a process known as demyelination.

Demyelination is the degeneration of a protective substance that insulates nerve axons (fibers) called myelin. In addition to protecting the axons, myelin also facilitates transmission of electrochemical impulses from nerve to nerve. When nerve axons become demyelinated, this process is drastically impaired and neurological impulses slow to a rate ten times less than normal. Neurologists frequently compare the loss of myelin and its effect on "conductivity" to the loss of insulating material around an electric wire.

The Neurological symptoms of demyelination include confusion, loss of motor ability, difficulty walking, changes in vision, muscle weakness, numbness and possible paralysis.

During relapses of multiple sclerosis (a well known type of a demyelinating disease) patches of demyelinated and inflamed neurons appear in the central nervous system (brain and spinal cord.) These patches are known as lesions. Oligodendrocytes (the cells that produces myelin) are also destroyed during MS relapses. The destruction of Oligodendrocytes prevents the quick rebuilding of myelin during remissions, a slow down which in turn allows scar tissue or "sclerotic" tissue to form in its place. The sclerotic tissue can not perform the same tasks as the myelin. These sclerotic lesions are known as "plaques" and will appear in multiple places through out the central nervous system. In more advanced cases of MS, some of the nerve axons themselves are destroyed during relapses.

The cause of demyelination is still unknown. It is generally believed that demyelination involves an autoimmune process. In other words, during demyelination a person's immune system attacks his or her central nervous system. Evidence of this is seen when Acquired Immune System Cells (T Cells) and macrophages (mobile white cells that speed up the process of Demyelination) are observed at lesions. What exactly triggers this response of the immune system is a question that is still being studied.

The FDA researchers advise that physicians prescribing either Remicade or Enbrel should be on the look out for early symptoms of demyelination such as difficulty walking, light headedness, confusion, and blurred vision. If such symptoms do occur the drug should be discontinued immediately and the patient referred to a neurologist for a complete examination. The researchers also advised that physicians treating patients known to have multiple sclerosis, other demyelinating diseases or related symptoms should consider alternatives to the drugs. Some doctors reacting to this recommendation advised that patients known to have these conditions should not be prescribed the drugs under any circumstances.