Causes Of Multiple Sclerosis And Treatment Methods
Multiple sclerosis (MS) is a chronic disease that attacks the central nervous system. It tends to be characterised by inflammation and degradation of myelin. Dr. Jean Martin Charcot (1825 – 1893), was the first person to scientifically explain and document this disease. Myelin affects roughly 1 in 600 people and there are 85,000 sufferers in the U.K today. Symptoms of MS tend to be seen between the ages of 20 and 40. This disease is more prevalent in women rather than men (NHS 2006). Multiple sclerosis can have affects on action potential conduction, as described below.
Causes
The degradation of myelin in MS sufferers is caused mainly through a process known as demyelination. Demyelination is the loss of myelin from a neurone. This leads to impaired impulses since nerve conduction is reduced and action potentials not being able to propagate properly; in some cases the impulses can be totally lost. Demyelination can lead to varied symptoms depending on the neurones that have been affected. Inflammation of the myelin can also lead to demyelination.
Demyelination causes reduced speed of action potentials because it reduces insulation around the axon and this can lead to ion leakage, through ion channels. This causes the depolarising effect of the neurone to be lost; this then translates into a reduced length constant. The overall effect of this is that the depolarising affect may not be able to reach the next node.
Capacitance also gets reduced through MS because more membrane becomes exposed to extracellular electrostatic forces and ions, so therefore more time and energy is needed to generate an action potential; reducing the propagation of an impulse.
The space constant is also affected since leakage of current occurs more often, and thus the time it takes for the depolarising effect to decay to 63% of its maximum is reduced. These effects all lead onto the various symptoms that are witnessed in MS suffers.
Symptomns
There are a variety of symptoms can be seen in MS sufferers. These include visual problems muscle weakness, fatigue, coordination problems, balance problems, sensations throughout the body and speech problems. Not all suffers have these symptoms and some who have all of the symptoms may not suffer from MS as these are present in other diseases. The only clear cut way to diagnose MS is through using the McDonald criteria (NHS 2006). This involves MRI scanning and testing cerebrospinal fluid from the patient.
The symptoms tend to start of mild but then they become more severe, as more damage occurs. The general underlying principle behind all the symptoms occurring is that demyelination occurs and as a result the action potentials cannot propagate effectively throughout the different neurones and depending on the neurone affected the related symptom’s are seen.
One of the following three symptom’s tend to be present in the majority of patients diagnosed with MS. These are optic neuritis, internuclear opthalmoplegia and transverse myelitis.
Transverse myelitis is the inflammation involving the spinal cord and this leads eventually to demyelination in MS. This causes weakness in the limbs and in severe cases patients may have to use wheelchairs to aid mobility. It also leads to problems with the sphincter muscle in the urinary system leading onto bladder and bowel dysfunction (Rucker 1996). These signs are seen because the action potentials cannot propagate correctly so therefore there is impaired movement. The contractions of muscles in the bladder and urethra cannot be coordinated properly because of the impaired action potential propagation from the spinal cord (NINDS 2003).
Internuclear opthalmoplegia is another symptom that tends to be characteristic of MS suffers. This is where the sufferer experiences double vision also known as binocular diplopia. This occurs when MS affects the neurones of the medial longitudinal fascicules. This is a centre in the brain stem that is responsible for communication and coordination between the two eyes. Thus leading onto the rectus muscles not contracting effectively and the eyes do not move in tune with each other producing double vision.
Optic neuritis is where there is sudden sharp striking pain in the eyes this then leads to blurry vision. This is down to the optic nerve becoming attacked by MS and the demyelination leading to ineffective impulse propagation.
Autoimmune disease
The exact cause of MS is still unknown however there are different theories as to how it may occur. The main theory states that MS is an autoimmune disease; whereby the patients own immune system attacks the nervous system. Multiple sclerosis is most likely to occur through a combination of genetic and environmental factors.
A special group of lymphocytes called T cells are involved in the progression of MS. These cells are a key part of the immune system and attack only foreign material however in MS they cannot distinguish between what is foreign and what is not, so therefore they attack parts of the CNS as if they were foreign material, thus leading to inflammation in the CNS and then on to activation of other immune responses (building up of antibodies, cytokines and macrophages). This then leads onto demyelination.
Treatment
MS does not have a definitive cure however there are various treatments that are available. The possibility of disease-modifying therapies allowed for treatment to be introduced to patients. (Freedman MS et al 2004).
These include interferon’s, which operate by regulating the immune system so that it does not cause as much damage to the CNS. Also Glatiramer acetate is used which helps convert T cells into anti inflammatory agents that help reduce inflammation.
There is also treatment available mainly in the form of drugs that help alleviate the symptom’s and allow for the patient to have a better quality of life. These include problems associated with the bladder and the bowel can be treated with the prescribed drug oxybutyin. Pains and numbness in the limbs can be treated through the use of baclofen. Amantadine can be used to treat the fatigue that arises from MS (Freedman MS et al 2004).
There are many studies being conducted which are looking into remyelination to help restore neurone function, however the neurons may not fully regenerate and still remain impaired (Ghatak NR 1989).
Technorati Tags: Multiple sclerosis, MS, myelin, demyelination, myelination, neurones, causes and treatments
