4.3. Multiple Sclerosis (MS)
Biological Processes Underlying MS
Multiple sclerosis (MS) is thought to be an autoimmune disease in which, over time, white blood cells (specifically T lymphocytes, although antibodies from B cells are implicated too) attack and strip away the myelin sheaths of neurons in the brain and spinal cord (this process is called demyelination). So MS is classified as an autoimmune disease as well as a progressive neuroinflammatory condition.
This results in inflammation around the neuron. The inflammation can clear but often reoccurs, and this permanently damages the neuronal axons and prevents them from conducting action potentials effectively. Recurrent damage to the neurons results in the formation of many sclerotic plaques, or scars, in the brain and spinal cord (hence the terms “multiple” and “sclerosis”). Without myelinated axons, neurons conduct action potentials at a much slower speed, or stop altogether. Another hallmark of MS is oligodendrocyte death – remember from Section 2.5. Glial Cells that oligodendrocytes are responsible for myelinating neurons in the CNS.
The cause of MS is unknown. However, it is likely due to a combination of environmental and genetic factors. One theory suggests that people are more likely to develop MS if they live further from the equator - this is why MS is relatively common in the UK and USA. The important link here may be vitamin D, which has a role in immunity; if you live further from the equator, you are exposed to less sunlight and therefore produce less vitamin D, and less vitamin D may contribute to the development of MS. A second theory proposes that some people have DNA that codes for abnormal myelin – this abnormal myelin is ‘antigenic’, making it a target for T lymphocytes. A third theory suggests that a viral infection may lead to such a strong response by the body's immune system that it begins to damage its own nervous tissue in addition to the virus, leading to the development of MS. A fourth theory suggests that smoking increases a person's risk of developing MS, although the mechanism of this is currently unclear. Evidence also indicates that stopping smoking slows the progression of MS.
It is known that MS affects approximately 1 in 1000 people in the UK. The progressive condition generally develops between the ages of 20 and 40 years. It is also twice as common in women as it is in men.
Types and diagnosis of MS
Types of MS
Those living with MS can go through periods of relapse and remission, with the below symptoms worsening during relapse. This type of MS is called relapse-remitting MS, and in many patients this type will eventually progress to secondary progressive type MS (in which symptoms are continually present). The other main type of MS is one where symptoms are constantly present from the outset and worsen over time, called primary progressive MS.
Symptoms
Visual disturbances (common)
This occurs due to inflammation in the optic nerve, called optic neuritis, and often presents as a unilateral (one-sided) blurring or greying of the visual field, like looking through petroleum jelly.
Sensory problems (common; sensory deficit)
This may include a sensation of wetness or burning over certain dermatomes - this is termed hemi-banding.
Muscle spasms and tremors (motor deficit)
This eventually leads to the shortening and permanent contraction of muscles (this is called spasticity).
Pain
There are two types of pain: neuropathic and musculoskeletal. Neuropathic pain occurs due to the damage to nerve fibres and leads to stabbing or burning sensations over the skin. Musculoskeletal pain is a result of the spasticity of muscles.
Fatigue
This is a common symptom, caused by the damage to the CNS or perhaps caused by side effects of medications or other MS symptoms. Fatigue can be severe and affect balance and concentration.
Depression, anxiety and stress
Perhaps due to damage to the CNS, dealing with the difficulties MS brings, or as a result of an individual’s psychological response to MS.
Making a Diagnosis
Diagnosing MS normally uses a set of criteria called the McDonald criteria. In essence, to meet the criteria, a patient needs to have displayed damage to their central nervous system ('disseminated' damage) across TIME and SPACE. This means that lesions need to appear in multiple areas over a number of months on MRI (note that MRI is the definitive imaging modality for MS).
Managing MS
Currently there is no cure for MS, although the symptoms can often be eased. Treatments can involve:
Medications
Immunomodulatory agents are available; these help to reduce the number of relapses in some casesand are often termed disease modifying therapies (DMTs). Examples are interferon beta and glatiramer. Steroids are also available; these reduce inflammation during a period of relapse.
Painkillers can be prescribed too, including amitriptyline (a tricyclic antidepressant) for neuropathic pain. Antidepressants are also available to treat depression and anxiety. Baclofen is a muscle relaxant used for muscle spasity.
Transcutaneous electrical nerve stimulation (TENS)
This is a chronic pain-relieving technique that involves attaching electrodes to the skin through which small electrical impulses are delivered; the electrical impulses can block or reduce the pain action potentials going to the spinal cord and brain.
Physiotherapy
This helps to maintain good function in tense and contracted muscles.
Occupational Therapy
This helps patients adjust their work and home environments as appropriate to their needs.
Psychological therapy
This helps patients to manage depression and anxiety, and deal with the difficulties that MS presents to patients.
