Demyelinating disease

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Demyelinating disease
MS Demyelinisation CD68 10xv2.jpg
Photomicrograph of a demyelinating MS-Lesion. Immunohistochemical staining for CD68 highlights numerous macrophages (brown). Original magnification 10×.
Classification and external resources
Specialty neurology
ICD-10 G35-G37, G61.0
ICD-9-CM 340-341, 357.0
DiseasesDB 17472
MeSH D003711

A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged.[1] This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency in sensation, movement, cognition, or other functions depending on which nerves are involved.

Some demyelinating diseases are caused by genetics, some by infectious agents, some by autoimmune reactions, and some by unknown factors. Organophosphates, a class of chemicals which are the active ingredients in commercial insecticides such as sheep dip, weed-killers, and flea treatment preparations for pets, etc., will also demyelinate nerves. Neuroleptics can also cause demyelination.[2] Lysophosphatidylcholine causes demyelination and is in unnaturally high amounts in foods with lecithin treated with the enzyme phospholipase (enzyme-modified foods) and as lysolecithin in products such as make up and personal care products. (See lysophosphatidylcholine.)

Demyelinating diseases are traditionally classified in two kinds: demyelinating myelinoclastic diseases and demyelinating leukodystrophic diseases. In the first group a normal and healthy myelin is destroyed by a toxic, chemical or autoimmune substance. In the second group, myelin is abnormal and degenerates.[3] The second group was denominated dysmyelinating diseases by Poser[4]

In the most known example, multiple sclerosis, there is good evidence that the body's own immune system is at least partially responsible. Acquired immune system cells called T-cells are known to be present at the site of lesions. Other immune system cells called Macrophages (and possibly Mast cells as well) also contribute to the damage.[5]

Causes[edit]

Some demyelinating diseases are caused by genetics, some by infectious agents, some by autoimmune reactions, some by exposure to chemical agents, and some by unknown factors.

Vitamin B12 deficiency (hypocobalaminemia)UNIQ--nowiki-00000010-QINU6UNIQ--nowiki-00000011-QINU: In 1926 the discovery that lack of Vitamin B 12 caused demylination of the spine and brain won Minot and Murphy the Nobel Prize. At the time this discovery highlighted the causes of Pernicious Anaemia. It was also learned that the ability to absorb Vitamin B12 orally by people over sixty years old tended to reduce. Anecdotally, it became common in Western medicine to inject B12 monthly in the form of Hydroxocobalamin for people over 60.

There are, however several pathways via which absorption of B12 may be affected and some people, of any age, cannot even absorb B12 via Hydroxocobalamin injections because they cannot convert it to methylcobablamin, its most useful form. A more direct form of IM injection is available, Methylcobalamin.

A number of ailments, diseases and medications can affect or even destroy ability to absorb B12 orally. There is also a common association between Hashimotos Disease, Lupus, Diabetes and Pernicious Anaemia. B12 deficiency is also sometimes misdiagnosed for Multiple Sclerosis, Alzheimers and other dementias, mental deficiencies, and autism.

Although injections are the most efficient, B12 in various forms is now also available sublingually as lozenges, but needs to be taken at a very high dose, such as 5000mcg (5 mg) daily for a month to achieve the same effect of one IM injection of 1000mcg (1 mg). People who are unable to absorb sufficient Vitamin B12 orally must continue to receive injections regularly for the rest of their lives. The frequency at which they require injections varies significantly according to information provided by the Pernicious Anaemia Society and self-help groups on Facebook. Initially, where there is neurological damage, according to the manufacturers of NeoB12 injections, for instance, they should be administered every second day for one to two weeks, then 4 monthly afterward. However most doctors will administer them monthly and many people with B12 deficiencies, notable pernicious anaemia, inject more frequently - sometimes daily. Anecdotally, the possibility of reversing reversible brain injury may be best if patients receive B12 IM every second day for up to six months or until symptoms stop improving. In Australia B12 is available over the counter, without prescription. In some other countries, it requires a prescription. The vitamin is water-soluble and easily excreted and the US Center for Disease Control have stated that it is safe at 1000 times the daily required level.

"Vitamin B12 is not carcinogenic, teratogenic, or mutagenic. It is considered safe even at 1,000 times the RDA." Baik and Russell, 1999, cited by the American Center for Disease Control, Baik and Russell, 1999, cited by the American Center for Disease Control

Some people experience transient acne in association with initial dosing up. Response is frequently rapid, within hours to 48 hours, although some people report it has taken up to 6 months to notice improvement.

For reasons speculated to be associated with insurance restructuring of diagnostic categories, and changes in diets, the common knowledge that B12 deficiencies could cause dementias, mental retardation, paralysis and death has been largely lost to medical graduates. Their awareness of B12 deficiency has trended largely to be restricted to the idea that it can cause macrocytic anaemia, with notably enlarged red blood cells, but the frequent presence of neurological problems before, if ever, the deficiency deforms the red blood cells, seems to have fallen off the diagnostic radar. The addition of folic acid to cereals in the 1990s, which prevents the enlargement of red blood cells typical of macrocytic anaemia has resulted in suppression of this one well-recognised sign of B12 deficiency. An additional complicating factor has been that B12 levels established as therapeutic in the United States, Australia and Britain at 150-700 picomol/L are very low, although pathology tests in Australia do recommend that, if there are neurological symptoms, patients should get B12 injections if their levels are less than 350 picomol/L. In comparison,Japan sets the healthy threshold at 500 picomol/L upwards.[7]

Because Vitamin B12 is obtained solely from animal products, including meat, seafood and dairy foods, Vegan diets do not contain any. Vegetarians may also not obtain enough. Children of vegans may be particularly at risk if the mother is low in B12 when breastfeeding. Severe vitamin B12 deficiency in infants breastfed by vegans; " Vegan Infants & Toddlers with B12 Deficiency." and https://www.vegansociety.com/resources/nutrition-health/vitamins-minerals-and-more/vitamin-b12-your-key-facts/what-every-vegan-should-know-about-vitamin-b12

Studies have found significant levels of B12 deficiency in children diagnosed with autism and elderly people with dementia.[8]

Evolutionary considerations[edit]

The role of prolonged cortical myelination in human evolution has been implicated as a contributing factor in some cases of demyelinating disease. Unlike other primates, humans exhibit a unique pattern of postpubertal myelination, which may contribute to the development of psychiatric disorders and neurodegenerative diseases that present in early adulthood and beyond. The extended period of cortical myelination in humans may allow greater opportunity for disruption in myelination, resulting in the onset of demyelinating disease.[9] Furthermore, it has been noted that humans have significantly greater prefrontal white matter volume than other primate species, which implies greater myelin density.[10] Increased myelin density in humans as a result of a prolonged myelination may therefore structure risk for myelin degeneration and dysfunction. Evolutionary considerations for the role of prolonged cortical myelination as a risk factor for demyelinating disease are particularly pertinent given that genetics and autoimmune deficiency hypotheses fail to explain many cases of demyelinating disease. As has been argued, diseases such as multiple sclerosis cannot be accounted for by autoimmune deficiency alone, but strongly imply the influence of flawed developmental processes in disease pathogenesis.[11] Therefore, the role of the human-specific prolonged period of cortical myelination is an important evolutionary consideration in the pathogenesis of demyelinating disease.

Signs and symptoms[edit]

Symptoms that present in demyelinating diseases are different for each condition. Below is a list of symptoms that can present in a person with a demyelinating disease.:[12]

  • Ocular paralysis
  • Impaired muscle coordination
  • Weakness (muscle)
  • Loss of sensation
  • Impaired vision
  • Neurological symptoms
  • Unsteady gait
  • Spastic paraparesis
  • Incontinence
  • Hearing problems
  • Speech problems

Diagnosis[edit]

Below are various methods/techniques used to diagnose Demyelinating Diseases.

Treatment[edit]

Treatment typically involves improving the patient's quality of life. This is accomplished through the management of symptoms or slowing the rate of demyelination. Treatment can include medication, lifestyle changes (i.e. quit smoking, adjusting daily schedules to include rest periods and dietary changes), counselling, relaxation, physical exercise, patient education and, in some cases, deep brain thalamic stimulation (in the case of tremors).[13] The progressive phase of MS appears to driven by the innate immune system, which will directly contribute to the neurodegenerative changes that occur in progressive MS. Until now, there are no therapies that specifically target innate immune cells in MS. As the role of innate immunity in MS becomes better defined, it may be possible to better treat MS by targeting the innate immune system.[14]

Treatments are patient-specific and depend on the symptoms that present with the disorder, as well as the progression of the condition.

Prognosis[edit]

Prognosis depends on the condition itself. Some conditions such as multiple sclerosis depend on the subtype of the disease and various attributes of the patient such as age, sex, initial symptoms and the degree of disability the patient experiences.[15] Life expectancy in Multiple sclerosis patients is 5 to 10 years lower than unaffected people.[16] MS is an inflammatory demyelinating disease of the central nervous system (CNS) that develops in genetically susceptible individuals after exposure to unknown environmental trigger(s).The bases for MS are unknown but are strongly suspected to involve immune reactions against autoantigens, particularly myelin proteins. The most accepted hypothesis is that dialogue between T-cell receptors and myelin antigens leads to an immune attack on the myelin-oligodendrocyte complex. These interactions between active T cells and myelin antigens provoke a massive destructive inflammatory response and promotes continuing proliferation of T and B cells and macrophage activation, which sustains secretion of inflammatory mediators.[17] Other conditions such as central pontine myelinolysis have about a third of patients recover and the other two thirds experience varying degrees of disability.[18] There are cases, such as transverse myelitis where the patient can begin recovery as early as 2 to 12 weeks after the onset of the condition.

Epidemiology[edit]

Incidence of demyelinating diseases vary from disorder to disorder. Some conditions, such as Tabes dorsalis appear predominantly in males and begins in mid-life. Optic neuritis on the other hand, occurs preferentially in females typically between the ages of 30 and 35.[19] Other conditions such as multiple sclerosis vary in prevalence depending on the country and population.[20] This condition can appear in children as well as adults.[16]

Types[edit]

Demyelinating diseases can be divided in those affecting the central nervous system and those presents in the peripheral nervous system, presenting different demyelination conditions. They can also be divided by other criteria in inflammatory and non-inflammatory, according to the presence or lack of inflammation, and finally, also a division can be made depending of the underlying reason for demyelination in myelinoclastic (myelin is attacked by an external substance) and leukodystrophic (myelin degenerates without attacks)

Demyelinating disorders of the CNS[edit]

The demyelinating disorders of the CNS include:

These disorders are normally associated also with the conditions Optic neuritis and Transverse myelitis, which are inflammatory conditions, because inflammation and demyelination are frequently associated. Some of them are idiopathic and for some others the cause has been found, like some cases of neuromyelitis optica.

Demyelinating diseases of the peripheral nervous system[edit]

The demyelinating diseases of the peripheral nervous system include:

Research[edit]

Research is being conducted in a variety of very specific areas. The focus of this research is aimed at gaining more insight into how demyelinating disorders affect the central nervous system and peripheral nervous system,[21][22][23][24][25] how they develop and how these disorders are affected by various external inputs[26][27][28][29][30] . Much of the research is targeted towards learning about the mechanisms by which these disorders function in an attempt to develop therapies and treatments for individuals affected by these conditions.

Insights[edit]

Currently it is believed that N-cadherin plays a role in the myelination process. Experimentation has shown that N-cadherin plays an important role in producing a remyelination-facilitating environment.[21] It has been shown in animal models that there is a direct correlation between the amount of myelin debris present and the degree of Inflammation observed.[22]

Effects of environmental inputs[edit]

Experimentation has shown that manipulating the levels of thyroid hormone can be considered as a strategy to promote remyelination and prevent irreversible damage in Multiple sclerosis patients.[24] N-cadherin agonists have been identified and observed to stimulate neurite growth and cell migration, key aspects of promoting axon growth and remyelination after injury or disease.[26] It has been shown that intranasal administration of aTf (apotransferrin) can protect myelin and induce remyelination.[28]

Much of the research referenced in this section has been conducted in 2012 and represents very new information about demyelinating diseases and potential therapies for them.

In Other Animals[edit]

Demyelinating diseases/disorders have been found worldwide in various animals. Some of these animals include mice, pigs, cattle, hamsters, rats, sheep, Siamese kittens, and a number of dog breeds (including Chow Chow, Springer Spaniel, Dalmatian, Samoyed, Golden Retriever, Lurcher, Bernese Mountain Dog, Vizsla, Weimaraner, Australian Silky Terrier, and mixed breeds).[31][32]

Another notable animal found able to contract a demyelinating disease is the Northern Fur Seal. Ziggy Star, a Northern Fur Seal, has been a patient at The Marine Mammal Center for the past several months and has been noted as the first case of such disease in a marine mammal. She will be transported to Mystic Aquarium & Institute for Exploration for lifelong care as an ambassador to the public.[33]

See also[edit]

References[edit]

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  31. ^ Merck Sharp & Dohme Corp (2011). "The Merck Veterinary Manual – Demyelinating Disorders: Introduction". Merck Veterinary Manual. Retrieved 2012-10-30. 
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  33. ^ "Ziggy Star has a Neurologic Condition". The Marine Mammal Center. Retrieved 2 February 2014.