By Dr Ananya Mandal, MD
The term demyelination refers to loss of the myelin sheath that surrounds and protects axons in the central nervous system.
The myelin sheath covers and insulates these axons, aiding the conduction of electrical signals between nerves. The process of demyelination disrupts this electrical nerve conduction, which leads to symptoms of neurodegeneration. Diseases that are characterized by this loss of myelin are referred to as demyelinating diseases. Some of the symptoms of demyelinating disease include impaired sensation, cognitive decline and impaired memory, movement and balance.
Several conditions lead to demyelination and one of the most well known of the neurodegenerative disorders is multiple sclerosis. Factors that are thought to contribute to the risk for demyelinating diseases include infection, autoimmune disorder, genetic predisposition, and exposure to toxins. Research has also shown that exposure to weed killers and insecticides containing organophosphates can cause demyelination. In addition, neuroleptic agents used in the treatment of psychosis have been shown to cause demyelination.
Areas of lipid degeneration in the myelin sheath are referred to as neuritic plaques. These may be variable in size. The residual degenerated myelin sheath is removed by macrophages that gather at the affected site along with lymphocytes. As time progresses, the sites of demyelination become gray and hard (sclerotic) as the white matter is destroyed. Eventually the destruction of the myelin sheath is followed by direct damage to the axon or nerve fibre underneath.
Reviewed by Sally Robertson, BSc