White matter of the brain consists of bundles of axons, elongated nerve cell fibres that are coated in a fatty white substance known as myelin. Axons function as a transport pathway for nerve signals, and myelin acts as an insulating coating that allows for greater speed of signal transmission, according to The Myelin Project. Degenerative diseases affecting white matter of the brain are those in which myelin is destroyed and nerve signals are interrupted. These demyelinating diseases can cause a wide variety of symptoms and can vary in their severity from mild to fatal.
Demyelinating diseases can be either acquired or hereditary. The hereditary disorders, known collectively as the leukodystrophies, result from genetic defects in the way myelin is produced by the body, according to The Myelin Project. Myelin damage is also seen in phenylketonuria or PKU, a genetic metabolic disorder in which the body is unable to utilise the essential amino acid phenylalanine.
The most common acquired demyelinating disease is multiple sclerosis, or MS. MS is thought to be an autoimmune disorder in which the body attacks its own myelin, causing damage and scarring. The cause of MS is unknown, but is thought to be a combination of a genetic predisposition and an environmental trigger that starts the onset of disease. MayoClinic.com also cites optic neuritis, Devic disease, transverse myelitis and acute disseminated encephalomyelitis as other examples of acquired demyelinating diseases.
Myelin destruction in the brain can give rise to a large number of motor (movement), sensory and cognitive symptoms. Acquired disease symptoms can include visual disturbance, muscle weakness and spasms, balance problems, paralysis, numbness and tingling, pain, headache, seizure, and cognitive decline, according to MayoClinic.com. Genetic demyelinating diseases are characterised by failure to thrive and develop normally in infancy, leading to vision and hearing loss, spasms and mental decline.
Treatments vary depending on the nature of the disease; however most focus on treating the symptoms of disease, as cures are not available. Treatments options include medications to ease pain and steroids to reduce inflammation. Disease-modifying drugs for MS are available and are thought to lessen the severity of myelin damage over time, according to the National Multiple Sclerosis Society. PKU can be controlled by following a strict, lifetime diet that is low in phenylalanine. Adrenoleukodystrophy, or ALD, is sometimes successfully prevented in presymptomatic children with a combination of vegetable oils known as Lorenzo's oil, according to The Myelin Project.
Prognoses for demyelinating disorders are highly variable. The leukodystrophies generally have poor outcomes resulting in death in childhood. Other disorders that can be tightly controlled, such as PKU, have the potential result of a normal life free of any symptoms. For acquired diseases such as MS, the severity of the disease is inconsistent from case to case; some people experience relatively few symptoms and recover fully from them, while others are subject to permanent damage resulting in visual loss, paralysis and even death, according to the National Multiple Sclerosis Society.