Demyelinating disorders of Central Nervous System

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]

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.

Vitamin B12 deficiency can cause demyelination.

Symptoms and signs that present in demyelinating diseases are different for each condition. Below is a list of symptoms and signs that can present in a person with a demyelinating disease.:[9]

  • Blurred double vision
  • Ataxia
  • Clonus
  • Dysarthria
  • Fatigue
  • Clumsiness
  • Hand paralysis
  • Hemiparesis
  • Genital anaesthesia
  • Incoordination
  • Paresthesias
  • Ocular paralysis
  • Impaired muscle coordination
  • Weakness (muscle)
  • Loss of sensation
  • Impaired vision
  • Neurological symptoms
  • Unsteady gait
  • Spastic paraparesis
  • Incontinence
  • Hearing problems
  • Speech problems

Demyelinating disorders of the CNS

The demyelinating disorders of the central nervous system include:

  • Myelinoclastic disorders, in which myelin is attacked by external substances
    • standard multiple sclerosis, Devic's disease and other disorders with immune system involvement called inflammatory demyelinating diseases.
  • Leukodystrophic disorders, in which myelin is not properly produced:
    • CNS neuropathies like those produced by vitamin B12 deficiency
    • Central pontine myelinolysis
    • Myelopathies like tabes dorsalis (syphilitic myelopathy)
    • leukoencephalopathies like progressive multifocal leukoencephalopathy
    • Leukodystrophies

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

The demyelinating diseases of the peripheral nervous system include:

  • Guillain–Barré syndrome and its chronic counterpart, chronic inflammatory demyelinating polyneuropathy
  • Anti-MAG peripheral neuropathy
  • Charcot–Marie–Tooth disease and its counterpart Hereditary neuropathy with liability to pressure palsy
  • Copper deficiency associated conditions (peripheral neuropathy, myelopathy, and rarely optic neuropathy)
  • Progressive inflammatory neuropathy

Diagnosis

Below are various methods/techniques used to diagnose demyelinating diseases.

  • Exclusion of other conditions that have overlapping symptoms[10]
  • Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to visualize internal structures of the body in detail. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body. This method is reliable because MRIs assess changes in proton density. "Spots" can occur as a result of changes in brain water content.[10]:113
  • Evoked potential is an electrical potential recorded from the nervous system following the presentation of a stimulus as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiological recording method.[10]:117
  • Cerebrospinal fluid analysis (CSF) can be extremely beneficial in the diagnosis of central nervous system infections. A CSF culture examination may yield the microorganism that caused the infection.[10]
  • Quantitative proton magnetic resonance spectroscopy (MRS) is a non-invasive analytical technique that has been used to study metabolic changes in brain tumors, strokes, seizure disorders, Alzheimer's disease, depression and other diseases affecting the brain. It has also been used to study the metabolism of other organs such as muscles.[10]:309
  • Diagnostic criteria refers to a specific combination of signs, symptoms, and test results that the clinician uses in an attempt to determine the correct diagnosis.[10]:320
  • Fluid-attenuated inversion recovery (FLAIR) uses a pulse sequence to suppress cerebrospinal fluid and show lesions more clearly, and is used for example in multiple sclerosisevaluation.

Treatment

Treatment typically involves improving the patient's quality of life and Immunotherapy (Corticosteroids, IVIG, Plasmapharesis/ Plasmaexchange and Immunosuppressive medications). This is accomplished through the management of symptoms or slowing the rate of demyelinating. 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).[10]:227–248 The progressive phase of MS appears 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.[11]

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