What is a Demyelinating Disease?
Any nervous system disease where there is damage to the myelin sheath of the neurons is known as a demyelinating disease. The damage to the myelin sheath diminishes the conduction of the signals in the nerves affected. This decrease in the conduction ability leads to deficiency in sensation, cognition, movement and other functions all of which depends on the nerves affected.
Types of Demyelinating Diseases
- Demyelinating diseases can be classified into those which affect the central nervous system and those which affect the peripheral nervous system.
- The other criteria for dividing is inflammatory and non-inflammatory, i.e. presence or lack of inflammation.
- Classification of the Demyelinating Diseases can also be made on the underlying cause of the demyelination, such as myelinoclastic where the myelin is destroyed by an external substance and leukodystrophic where the myelin degenerates on its own without attacks. In demyelinating myelinoclastic diseases the normal and healthy myelin is damaged by an autoimmune substance, toxic or chemical. In demyelinating leukodystrophy disease, the myelin is abnormal and degenerates.
Demyelinating Diseases of the Central Nervous System
- Myelinoclastic disorders where the myelin sheath gets damaged from external substances.
- Inflammatory demyelinating diseases comprise of Devic's disease, standard multiple sclerosis, and disorders which have involvement of the immune system.
- Leukodystrophy disorders is where the myelin sheath is not properly produced and comprise of CNS neuropathies due to vitamin b12 deficiency, leukoencephalopathies such as progressive multifocal leukoencephalopathy, central pontine myelinolysis, myelopathies like syphilitic myelopathy,
- Demyelinating diseases of the Central Nervous System are commonly associated with conditions, such as transverse myelitis and optic neuritis. These are inflammatory conditions as demyelination is frequently associated with inflammation. Some of these conditions are idiopathic.
Demyelinating Diseases of the Peripheral Nervous System
- Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy, which is the chronic counterpart of Guillain-Barré syndrome.
- Charcot–Marie–Tooth disease.
- Anti-MAG peripheral neuropathy.
- Progressive inflammatory neuropathy.
- Conditions associated with copper deficiency such as peripheral neuropathy, myelopathy, and rarely optic neuropathy.
Causes of Demyelinating Diseases
- The cause of demyelinating diseases can be genetics, infectious agents, autoimmune reactions, and other unidentified factors.
- Organophosphates are a category of chemicals present in commercial insecticides, such as weed-killers, sheep dip and flea treatment preparations, which can also demyelinate the nerves.
- Demyelination can also occur with the use of neuroleptics.
- Deficiency of vitamin B12 can also cause demyelination.
- Multiple sclerosis is a common example of a demyelinating disease, where the body's own immune system is partially responsible for destruction of the myelin sheath. T-cells, which are acquired immune system cells, are present at the site of lesions. Macrophages and possibly Mast cells can also cause damage to the myelin sheath.
Signs & Symptoms of Demyelinating Diseases
Symptoms of demyelinating diseases vary with each condition. Given below are some of the common symptoms which can be seen with demyelinating diseases:
- Blurred double vision.
- Problems with speech.
- Paralysis of the hands.
- Genital anesthesia.
- Ocular paralysis.
- Muscle weakness.
- Vision impairment.
- Loss of sensation.
- Unsteady gait.
- Impaired muscle coordination
- Neurological symptoms.
- Spastic paraparesis.
- Problems with hearing.
Diagnosis of Demyelinating Diseases
- Other conditions which can have overlapping symptoms same as of demyelinating diseases should be excluded.
- Magnetic resonance imaging (MRI) is a radiological test done to visualize the internal structures of the body in detail. However, this test can be unreliable as the MRI assesses the changes in the proton density and "spots" can also be seen due to changes in the content of the brain water.
- Evoked potential is a test where an electrical potential is recorded from the nervous system after the detection of the stimulus.
- Quantitative proton magnetic resonance spectroscopy is a non-invasive analytical test, which is used to study the metabolic changes in brain due to strokes, tumors, seizure disorders, depression, Alzheimer's disease and other brain diseases.
- Cerebrospinal fluid (CSF) analysis is an extremely beneficial test for diagnosing infections in the central nervous system. Culture of the Cerebrospinal fluid helps in identifying the microorganism which causes the infection.
- Diagnostic criteria is a combination of test results, signs and symptoms which will help the doctor in arriving at the correct diagnosis.
Treatment for Demyelinating Diseases
- Treatment for a demyelinating disease is aimed at improving the patient's quality of life by managing the patient's symptoms and slowing the rate of demyelination.
- Treatment for demyelinating diseases differs from patient to patient and depends on the symptoms and progression of the disorder.
- Treatment comprises of medication, lifestyle changes, counseling, physical exercise, relaxation, patient education and deep brain thalamic stimulation if needed, such as in the case of tremors.
- Lifestyle changes include adjusting daily schedules, quitting smoking, having a balanced diet, getting adequate rest etc.
- The progressive stage of multiple sclerosis, which is a demyelinating disease, is thought to be driven by the immune system, which has a direct impact on the neurodegenerative changes which are seen in progressive multiple sclerosis. Till date there is no treatment which speciﬁcally targets the innate immune cells in multiple sclerosis. Research is still going on to better define the role of the innate immunity in multiple sclerosis so that treatment of it can be possible by targeting the innate immune system.
Prognosis of Demyelinating Diseases
Prognosis of Demyelinating Diseases depends on the condition. Prognosis of some conditions, such as multiple sclerosis, depends on the subtype and other factors such as sex, age, initial symptoms and the extent of the disability which the patient has. Life expectancy in patients with multiple sclerosis is around 5 to 10 years lesser than a healthy individual. Multiple sclerosis is an inflammatory demyelinating disease which affects the central nervous system. Individuals who are genetically susceptible tend to develop this condition after exposure to unknown environmental triggers.