Multiple sclerosis (MS) affects conduction in axons within in the CNS by damaging the myelin sheath provided by the oligodendrocytes.
MS is an immune-mediated inflammatory disease of the oligodendrocytes; inflammation generates plaques, areas of sclerosis within the brain.
Plaques are thought to be due to a breakdown locally of the blood-brain barrier, an infiltration of lymphocytes and macrophages, and the activation of microglia.
The myelin of the peripheral nervous system provided by Schwann cells is not affected by this disease.
This results in patients having problems with muscle movement, balance and vision. Patients also feel fatigue.
Patients with MS may experience symptoms either intermittently or building up fairly continuously over time (relapsing and progressive forms).
Between attacks, the symptoms may disappear completely, but more commonly the neurological problems become permanent, especially as the disease advances.
Image source: Wikipedia
MRI image of the spinal cord of a patient with Multiple Sclerosis. The extent of the lesions can be seen in the MRI reconstruction of this patient's spinal cord.
Multiple sclerosis (MS) is an inflammatory disease in which the myelin sheaths around CNS axons are damaged. While the cause is not clear, the underlying mechanism is thought to be either destruction of CNS myelin by the inmmune system (autoimmunity), or a failure of production of myelin.
The long-term outcome is not easily predictable, but the disorder can be divided into several different clinical presentations:
Relapsing-Remitting MS (RRMS) - the most common form of multiple sclerosis. People with RRMS have relapses, i.e. episodes of flare-ups or exacerbations, when new symptoms appear.
Secondary-Progressive MS (SPMS) - many people with RRMS move into this phase of the disease : symptoms worsen more steadily over time.
Primary-Progressive MS (PPMS) - an uncommon form of MS in which symptoms worsen more or less continuously without relapses or remissions.
Progressive-Relapsing MS (PRMS) - A rare form of MS characterized by symptoms that worsen steadily from the beginning.
Good outcomes are more common in females and in affected young people, and in those with a relapsing course particularly if they have only had a few attacks.
Evoked potential techniques have proved useful in screening for demyelination because of the slowing in axonal conduction associated with the loss of oligodendrocytes. One example is the use of the Visual Evoked Potential that shows slowing of conduction in patients with optic neuritis: these patients may have temporary loss or blurring of vision, double vision, or a lack of coordination between the two eyes.
One hypothesis is that the blood brain barrier is breached because of infection, such as a viral infection. The entry of T-lymphocytes, activated by the virus, into the CNS is thought to cause an autoimmune attack on oligodendrocytes, resulting in a loss of myelin.
Remyelination starts but is incomplete, and repeated immune attacks cause relapses, that worsen the demyelination process.
Scars, sclerosis, occur in the white matter because of astrocytic hypertrophy. These scars are often adjacent to the ventricular system, ventricles or central canal of the spinal cord.
Carswell's 1838 image of the lesions in the brainstem and spinal cord of a patient with MS
Distribution of demyelinated lesions (plaques)
The diagram shows that plaques can be distributed throughout the CNS and produce signs and symptoms according to which Pathays are affected by these lesions. Signs and Symptoms commonly include:
Visual problems including temporary loss or blurring of vision, double vision, or a lack of coordination between the two eyes. Vision may vary depending on the time of day or the circumstances - for example, it might get worse when you are stressed, tired or in unfamiliar surroundings.
Balance problems and dizziness: Symptoms might mean patients are wobbly on their feet from time to time, or might need to move with more care than before to avoid losing balance. THee may be associated with brainstem or cerebellar lesions
Stiffness or Spasms: affect at least 20 per cent of people with MS at some time. Like all MS symptoms, spasms and stiffness affect people differently and can vary over time. Stiffness of muscles is controlled by the brainstem reticular formation
Speech difficulties of some kind affect between 40 and 50 per cent of people with MS. More details of the pathways involved can be found in the specific sections on motor control in Tutorials 5, 6 and 7.
There are two main types of bladder problems in MS - storage and emptying - causing urinary retention or incontinence. Constipation is more common in MS than bowel incontinence.
MS can affect sexual function for both men and women
Fatigue in MS is not just an ordinary tiredness, but an overwhelming sense of tiredness that often occurs after very little activity, and is probably related to the inflammatory processes involved in MS pathology.
Image source: WHO2004
MS is more common in areas further away from the equator. It is virtually unheard of in places like Malaysia or Ecuador, but relatively common in Britain, North America, Canada, Scandinavia, southern Australia and New Zealand.
It is not clear why people further away from the equator are more likely to get MS, but it is possible that something in the environment, perhaps bacteria or a virus, plays a role.
No single virus has been identified as definitely contributing to MS, but there is growing evidence that a common childhood virus, such as Epstein Barr virus (which can cause glandular fever), may act as a trigger.
This theory is still unproven and many people who do not have MS would have also been exposed to these viruses, so just like genes, they are unlikely to be the whole story.
Vitamin D is involved in neural development and in neuroplasticity. There is also a growing amount of research that suggests that a lack of vitamin D could be a factor in causing MS.
We get most of our vitamin D from exposure to sunlight. Low levels of vitamin D have been linked to higher numbers of people developing many different conditions, including MS. The demographic distribution of MS is shown in the accompaying map.
A number of studies have looked at smoking in relation to MS, and have found that smoking appears to increase the risk of developing MS. It's not yet clear exactly why this is.