Multiple sclerosis is a chronic disorder of the central nervous system mediated by autoimmunity against myelin sheath, which leads to demyelination and resulting symptomatology. It has female preponderance, affecting individuals in their 20-50s. The cause of MS is still unknown and is thought to be a confluence of genetic and environmental factors leading to autoimmunity.
The clinical course of MS is very unpredictable and varies from patient to patient. The first event of any neurological symptom that lasts for more than 24 hours, characteristic of MS, which may or may not be accompanied by a lesion on brain MRI, is known as CIS (clinically isolated syndrome). However, CIS does not meet the criteria for a diagnosis of MS as it may or may not progress into MS.
There is yet another form, known as RIS or radiologically isolated syndrome that is associated with MS like lesions on MRI, which are not explained by another diagnosis and the patient being negative for any past/present neurological symptoms. These lesions are accidentally diagnosed on scan done for another purpose, such as headache or head injury. These patients also do not fall in the criteria for a diagnosis of MS, but they need follow up, in case they progress into MS.
What Are The 4 Types Of MS?
Based on the clinical course of MS, neurologists have classified patients under four categories. These include.
Relapsing-Remitting MS (RRMS). This is the most common type of MS that affects nearly 85% of all multiple sclerosis patients. As the name implies, it is characterized by periods of exacerbations of flare-ups, in which there are presentation of symptoms followed by periods of recovery, in which the symptoms disappear or may become permanent. The periods of relapse may also be marked with new lesions on MRI in active forms of RRMS; however, in non-active forms, there is no progression of the disease seen on MRI. The periods of relapse may be short lived for some patients and may last longer for other patients (from few days to months) and the same can be said for periods of remission.
Secondary Progressive MS (SPMS). This is characteristic of progressive disability of multiple sclerosis that started as relapsing-remitting MS, therefore, it is known as secondary progressive MS as it occurred secondary to RRMS. In this the patient may experience relapses of symptoms with active MRI lesions, but the recovery may not be complete and the persisting symptoms may become permanent that may lead to progressive worsening of the disease and increased disability. In a course of 10 years, about 50% patients with RRMS progress to SPMS, if left untreated.
Primary Progressive MS (PPMS). This is a less common form of MS, affecting 10% of all MS patients. In this form of disease, the disease progresses steadily from the very beginning. There are no periods of relapses and remissions in this form of disease.
Progressive Relapsing MS. This is also a very rare form of multiple sclerosis that affects less than 5% of all multiple sclerosis cases. In this the disease is worsening and progressive from the beginning with occasional periods of relapse or flare-ups without any periods of remission.
Although, there exists no permanent cure for the disease, there are various FDA approved disease modifying therapies that limit the progression of the disease and help minimize disability. These help in shortening the periods of acute exacerbations, decreasing the frequency of flare-ups and also providing symptomatic relief to improve the quality of life. Acute periods of exacerbation can be treated with short course of steroids. The disease modifying agents approved by FDA include beta interferons (Avonex, Extavia, Rebif, Betaseron), glatiramer acetate (Copaxone), mitoxantrone (Novantrone), natalizumab (Tysabri), and fingolimod (Gilenya).
Dalfampridine is FDA approved drug used to improve symptoms of walking in MS patients. There are other drugs not approved by FDA, which include methotrexate, azathioprine, cyclophosphamide, cladribine and mycophenolate mofetil that are used therapeutically for MS patients.
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