Multiple sclerosis (MS) is an autoimmune disease where the immune system attacks myelin, the insulating cover of nerve cells in the human body, causing damage to one's own central nervous system. It is a type of demyelinating disease, where the nervous system's ability to transmit signals is damaged. Symptoms can be physical, mental, or both, including double vision, vision loss, eye pain, muscle weakness, loss of sensation and coordination. While its cause is unclear, the underlying mechanism is thought to be due to either destruction by the immune system or inactivation of myelin-producing cells. Proposed causes for this include immune dysregulation, genetics, and environmental factors, such as viral infections. The McDonald criteria are a frequently updated set of guidelines used to establish an MS diagnosis. There is no cure for MS. Current treatments aim to reduce inflammation and manage symptoms during acute flares and prevent further attacks with disease-modifying therapies. These approaches seek to improve quality of life by slowing disease progression. Physical therapy and occupational therapy, along with patient-centered symptom management, can help improve functional ability. The long-term outcome is difficult to predict; however, better outcomes are more commonly seen in women, those who develop the disease early in life, those with a relapsing course, and those who initially experience fewer attacks. MS is the most common immune-mediated disorder affecting the central nervous system (CNS). In 2020, about 2.8 million people were affected by MS globally, with rates varying widely in different regions and among different populations. The disease usually begins between the ages of 20 and 40 and is almost three times more common in females than in males (3:1 ratio). MS was first described in 1868 by French neurologist Jean-Martin Charcot. The name "multiple sclerosis" is short for multiple cerebro-spinal sclerosis, which refers to the numerous glial scars (or sclerae – essentially plaques or lesions) that develop on the white matter of the brain and spinal cord.
Signs and symptoms
Because MS lesions can affect any part of the central nervous system, a person with MS can have almost any neurological signs or symptoms. Fatigue is one of the most common symptoms of MS. Roughly 65% of people with MS experience fatigue. Of these, some 15–40% report fatigue as their most disabling symptom. Autonomic, visual, motor, and sensory problems are also among the most common symptoms. The specific symptoms depend on the locations of the lesions within the nervous system and may include loss of sensitivity or changes in sensation in the limbs, such as tingling, "pins and needles", or numbness; limb motor weakness or pain, blurred vision, pronounced reflexes, muscle spasms, difficulty walking, or with coordination or balance (ataxia); problems with speech or swallowing, visual problems (optic neuritis manifesting as eye pain and vision loss, or nystagmus manifesting as double vision), fatigue, and bladder and bowel difficulties (such as urinary or fecal incontinence or retention), among others. When MS is more advanced, walking difficulties lead to a higher risk of falling. Difficulties in thinking and emotional problems such as depression or unstable mood are also common. The primary deficit in cognitive function that people with MS experience is slowed information-processing speed, with memory also commonly affected, and executive function less commonly. Intelligence, language, and semantic memory are usually preserved, and the level of cognitive impairment varies considerably between people with MS. Uhthoff's phenomenon, a reversible exacerbation of symptoms following a rise in body temperature, and Lhermitte's sign, an electrical sensation that runs down the back when flexing the neck, are particularly characteristic of MS, although may not always be present. 60–80% of MS patients find that symptoms, such as fatigue, are affected by changes in body temperature. MS may also present with eye movement impairments, such as internuclear ophthalmoplegia or sixth nerve palsy.
Measures of disability The main measure of disability and severity is the expanded disability status scale (EDSS), with other measures such as the multiple sclerosis functional composite being increasingly used in research. EDSS is also correlated with falls in people with MS. While it is a common measure, EDSS has been criticized for some of its limitations, such as overreliance on walking.
Disease course
Prodromal phase MS may have a prodromal phase in the years leading up to its manifestation, characterized by psychiatric issues, cognitive impairment, and increased use of healthcare.
Onset 85% of cases begin as a clinically isolated syndrome (CIS) over a number of days with 45% having motor or sensory problems, 20% having optic neuritis, and 10% having symptoms related to brainstem dysfunction, while the remaining 25% have more than one of the aforementioned difficulties. With optic neuritis as the most common presenting symptom, people with MS notice sub-acute loss of vision, often associated with pain worsening on eye movement, and reduced color vision. Early diagnosis of MS-associated optic neuritis helps timely initiation of targeted treatments. However, it is crucial to adhere to established diagnostic criteria when treating optic neuritis due to the broad range of alternative causes, such as neuromyelitis optica spectrum disorder (NMOSD), and other autoimmune or infectious conditions. The course of symptoms occurs in two main patterns initially: either as episodes of sudden worsening that last a few days to months (called relapses, exacerbations, bouts, attacks, or flare-ups) followed by improvement (85% of cases) or as a gradual worsening over time without periods of recovery (10–15% of cases). A combination of these two patterns may also occur, or people may start in a relapsing and remitting course that then becomes progressive later on.
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