Multiple sclerosis (MS) is an unpredictable, disabling disease of the central nervous system. Once MS begins, usually in early adulthood, it is a lifelong condition which can range in severity from benign to devastating, with most patients falling between these two extremes. The damage caused by MS results from inflammation within the brain, optic nerves, or spinal cord (the central nervous system). While the trigger for this inflammation remains unknown, most researchers believe MS is an autoimmune disease, in which the immune system attacks the nerve-insulating myelin which coats nerve fibers and enables them to function normally. The initial trigger for MS most likely comes from the environment, possibly a virus, but once the disease is established, it continues of its own accord, driven by the immune system’s attack on healthy tissue.

The damage caused by the immune system in MS occurs only in the central nervous system. MS does not cause direct harm to the muscles, the nerves outside the central nervous system, or to other organs in the body. However, over time MS patients may experience neurological problems such as weakness, sensory loss, or bladder dysfunction. Without appropriate management, these problems can lead to other medical complications, so it is important for patients living with MS to have regular follow-up with both a neurologist and a general medical doctor, such as an internist or family medicine specialist. Since MS can strike almost anywhere in the central nervous system, MS can present with a wide range of symptoms. Early in the disease, MS symptoms are often transient, making it difficult for patients and their doctors to recognize the earliest symptoms of the disease. 

Most people experience their first symptoms of MS between the ages of 20 and 40. However, MS can strike in childhood and well into a person’s 60s. The younger the patient, the more likely MS will begin with a series of relapses. Also referred to as attacks, bouts, flare-ups, or exacerbations, relapses tend to develop over hours to days, sometimes taking weeks to reach maximum severity. In most cases, the symptoms will begin to improve on their own, sometimes resolving completely, and at other times leaving an individual with residual neurological symptoms which may not ever go away. Over time, repeated relapses can lead to increasing disability. The development of disease modifying therapies, discussed below, has led to reduced numbers of relapses in most patients and decreased disability over time. Increasing evidence supports starting a disease modifying therapy soon after a diagnosis is made, to lessen the long-term impacts of MS.

A minority of MS patients may experience ‘progressive’ symptoms instead of relapses at the onset of their disease. Progressive symptoms develop much more slowly (over months to years) with little to no improvement over time. Patients with progressive-onset MS tend to be in their 40s or older.