Multiple sclerosis (abbreviated MS, also known as disseminated sclerosis or encephalomyelitis disseminata) is an autoimmune condition in which the immune system attacks the central nervous system, leading to demyelination. Disease onset usually occurs in young adults, and it is more common in females. It has a prevalence that ranges between 2 and 150 per 100,000. MS was first described in 1868 by Jean-Martin Charcot.
MS affects the ability of nerve cells in the brain and spinal cord to communicate with each other. Nerve cells communicate by sending electrical signals called action potentials down long fibers called axons, which are wrapped in an insulating substance called myelin. In MS, the body’s own immune system attacks and damages the myelin. When myelin is lost, the axons can no longer effectively conduct signals. The name multiple sclerosis refers to scars (scleroses – better known as plaques or lesions) in the white matter of the brain and spinal cord, which is mainly composed of myelin. Although much is known about the mechanisms involved in the disease process, the cause remains unknown. Theories include genetics or infections. Different environmental risk factors have also been found.
Almost any neurological symptom can appear with the disease, and often progresses to physical and cognitive disability. MS takes several forms, with new symptoms occurring either in discrete attacks (relapsing forms) or slowly accumulating over time (progressive forms). Between attacks, symptoms may go away completely, but permanent neurological problems often occur, especially as the disease advances.
There is no known cure for MS. Treatments attempt to return function after an attack, prevent new attacks, and prevent disability. MS medications can have adverse effects or be poorly tolerated, and many patients pursue alternative treatments, despite the lack of supporting scientific study. The prognosis is difficult to predict; it depends on the subtype of the disease, the individual patient’s disease characteristics, the initial symptoms and the degree of disability the person experiences as time advances. Life expectancy of patients is nearly the same as that of the unaffected population.
Symptoms of MS usually appear in episodic acute periods of worsening (relapses, exacerbations, bouts or attacks), in a gradually-progressive deterioration of neurologic function, or in a combination of both.
The most common presentation of MS is the clinically isolated syndrome (CIS). In CIS, a patient has an attack suggestive of demyelination, but does not fulfill the criteria for multiple sclerosis. Only 30 to 70% of persons experiencing CIS later develop MS. The disease usually presents with sensorial (46% of cases), visual (33%), cerebellar (30%) and motor (26%) symptoms. Many rare initial symptoms have also been reported, including aphasia, psychosis and epilepsy. Patients first seeking medical attention commonly present with multiple symptoms. The initial signs and symptoms of MS are often transient, mild, and self-limited. These signs and symptoms often do not prompt a person to seek medical attention and are sometimes identified only retrospectively once the diagnosis of MS has been made. Cases of MS are sometimes incidentally identified during neurological examinations performed for other causes. Such cases are referred to as subclinical MS.
The person with MS can suffer almost any neurological symptom or sign, including changes in sensation (hypoesthesia and paraesthesia), muscle weakness, muscle spasms, or difficulty in moving; difficulties with coordination and balance (ataxia); problems in speech (dysarthria) or swallowing (dysphagia), visual problems (nystagmus, optic neuritis, or diplopia), fatigue, acute or chronic pain, and bladder and bowel difficulties. Cognitive impairment of varying degrees and emotional symptoms of depression or unstable mood are also common. The main clinical measure of disability progression and symptom severity is the Expanded Disability Status Scale or EDSS.
Multiple sclerosis relapses are often unpredictable, occurring without warning and without obvious inciting factors. Some attacks, however, are preceded by common triggers. Relapses occur more frequently during spring and summer. Infections such as the common cold, influenza, or gastroenteritis increase the risk of relapse. Stress may also trigger an attack. Pregnancy may affect susceptibility to relapse, offering protection during the last trimester, for instance. During the first few months after delivery, however, the risk of relapse is increased. Overall, pregnancy does not seem to influence long-term disability. Many potential triggers have been examined and found not to influence MS relapse rates. There is no evidence that vaccination for influenza, hepatitis B, varicella, tetanus, or tuberculosis increases risk of relapse. Physical trauma does not trigger relapses. Exposure to higher than usual ambient temperatures can exacerbate extant symptoms, an effect known as Uhthoff’s phenomenon. Uhthoff’s phenomenon is not, however, an established relapse trigger.