What is multiple sclerosis?
Multiple sclerosis is an immune-mediated inflammatory disorder of the central nervous system (brain and spinal cord). “Immune mediated” means that the immune system gets mixed up and essentially starts mounting an attack against itself. In multiple sclerosis the primary site of this attack is at the myelin sheath. Myelin is a fatty substance that surrounds and insulates nerve fibres. You can liken it to electrical wires with surrounding insulation. The nerve fibres themselves are the “wires” and the myelin is the insulation material surrounding the nerve fibre or “wire”. When the myelin is stripped back it leaves a scar on the brain and this is called “sclerosis”. This is where the disease gets its name- multiple areas of myelin loss or sclerosis.
When this insulation is lost the nerve impulses will be transmitted too slowly or not at all. This leads to a communication breakdown between the signals leaving your brain and reaching the rest of your body. This is what ultimately leads to the symptoms of multiple sclerosis. The area of the brain that has lost its myelin will dictate what type of symptoms you will get. When an area of myelin is lost and you get symptoms- this is referred to as a relapse or attack of multiple sclerosis.
In addition to the loss of myelin there can be degeneration of the nerve cells themselves over time. This is referred to as neurodegeneration and it shows up on the brain scan as thinning of areas of the brain or widening of the fluid filled spaces in the brain and this is referred to as brain “atrophy”.
- The impact of multiple sclerosis varies according to a number of measures including:
- Severity of signs and symptoms- for example if the symptoms you have are mainly sensory ones like numbness, tingling or even pain this may be far easier to deal with than weakness and stiffness in the legs.
- Frequency of attacks- this is highly variable between individuals. Attacks may be more common after stressful life events.
- Residual disability following relapses- if following a relapse there is incomplete recovery this disability may accumulate over time.
- There are a number of types of multiple sclerosis:
- Relapsing-Remitting Multiple Sclerosis (RRMS)- This is the most common form of multiple sclerosis. It is defined by relapses during which the patient will experience symptoms. The symptoms tend to come on over a few days, last a number of weeks and then resolve over a number of weeks. Following the relapse there can be a complete resolution of symptoms or it can be partial. There should be minimal disease progression during periods between relapses although the relapses themselves may leave some residual disability.
- Secondary Progressive Multiple Sclerosis (SPMS)- This is diagnosed where there was originally a diagnosis of RRMS but over time there was gradual worsening of symptoms with or without occasional relapses without full recovery in between. In other words a patient who has been diagnosed with RRMS and then over time gradually deteriorates. The diagnosis of SPMS is made only in retrospect.
- Primary Progressive Multiple Sclerosis (PPMS)- In this type of multiple sclerosis there is progressive accumulation of disability from disease onset. There may still be the occasional relapse or temporary improvement but ultimately the hallmark is a gradual continuation of disability. These patients may present at a slightly later age and may have a slightly worse prognosis overall in terms of disability than patients who initially fall in to the RRMS disease category.
- Benign Multiple Sclerosis- This refers to disease in which the patient remains fully functional 15 years after disease onset- this is always a retrospective diagnosis.
- Malignant Multiple Sclerosis- this is a very aggressive form of multiple sclerosis. It is defined by the need for assistance with walking within 5 years of disease onset.
- Clinically isolated syndrome- this is considered the first attack of symptoms consistent with multiple sclerosis with a lot of the characteristic findings but just failing to meet the diagnosis. If there are white spots on the brain at the time of these symptoms there is a higher overall chance of developing multiple sclerosis over time. If there are no white spots found on the brain scan at the time of the symptoms there is a much lower chance of eventually developing multiple sclerosis.
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