Speaking Multiple Sclerosis: A Glossary of Common Terms

Whether you’ve been recently diagnosed with multiple sclerosis (MS) or have been living with the condition for a while, chances are you’ll sometimes hear terms from your healthcare team that are new to you.

The following is a quick, alphabetical guide to the terminology you may need to know as you manage your condition:

Ankle-Foot Orthosis (AFO) A brace designed to support the position of the foot and motion of the ankle to compensate for nerve damage and muscle weakness in the area caused by MS and other movement disorders. An AFO is typically used to stabilize weak limbs or to reposition a limb with contracted muscles into a more normal position.

Annualized Relapse Rate This is the average number of relapses that occur within a group of people with MS in one year. It’s often used as a measure of a drug’s effectiveness in clinical research trials.

For example, if in a group of 100 people with MS, each person had 1 relapse, that would total 100 relapses over that year; the average number of relapses that each individual experienced would be 1, and hence the annualized relapse rate would also be 1.

In another example, if out of 100 people with MS, 50 people have 2 relapses and 50 people don’t have any, the average would again be 1, and the annualized relapse rate would also be 1.

Autoimmune Disease Your immune system plays a major part of your body’s defense against bacteria and viruses by sending out cells to attack them once they enter your body. However, if you have an autoimmune disease, your immune system mistakenly attacks healthy cells in your body, causing them to weaken or break down. MS is thought to be just one example of an autoimmune disease. It has been suggested that in MS, your immune system may mistakenly attack the cells in your central nervous system.

Axon Long threadlike structures of nerve cells that send impulses to other cells in your body. Research suggests that damage to or loss of these fibers in progressive MS may be linked to worsening disability and more severe progression.

Central Nervous System (CNS) The group of organs in your body that includes the brain, spinal cord, and optic nerves. If you have MS, your body’s immune system may be working against the CNS, producing neurological symptoms such as muscle weakness and vision problems.

Cerebrospinal Fluid (CSF) A clear, colorless liquid that surrounds the brain and spinal cord to protect the CNS and assist in the circulation of nutrients and removal of waste products. In MS, damage to the myelin sheath of nerve cells causes certain types of proteins to be released into the spinal fluid. The presence of these proteins in the CSF, but not in the blood, may point to a diagnosis of MS.

Clinically Isolated Syndrome (CIS) A first episode of neurologic symptoms that lasts at least 24 hours and is caused by inflammation or demyelination (loss of the myelin that covers the nerve cells) in the CNS. People who experience CIS may or may not go on to develop MS. However, when CIS is accompanied by magnetic resonance imaging (MRI)–detected brain lesions similar to those found in MS, you have a 60 to 80 percent chance of a second neurologic event and diagnosis of MS within several years, according to the National MS Society.

Cog Fog A commonly used term that refers to the cognitive changes experienced by many people with MS. According to MS Australia, approximately 50 percent of people with the condition will develop some degree of cog fog, or inhibited ability to think, reason, concentrate, or remember. For some, cognitive problems will become severe enough to interfere in a significant way with daily activities.

Corticosteroids (or Steroids) Prescription medication used to treat relapses in relapsing-remitting MS. Your doctor may prescribe intravenous (IV) corticosteroids if the symptoms of your relapse are causing significant problems, like poor vision or difficulty walking. These drugs work by suppressing the immune system and reducing inflammation in the CNS, and they may help relapse symptoms resolve more quickly. But they won’t affect your ultimate level of recovery from a relapse or the long-term course of your MS. Methylprednisolone is a commonly used corticosteroid in MS.

“Crap Gap” This is a slang term for the period between Ocrevus (ocrelizumab) infusions (delivered by an IV in the arm every six months) when a person feels their MS symptoms worsening. The “gap” can occur in the final few weeks before the next infusion is scheduled when the medication may be wearing off and continue for a short time after the infusion until the medication has a chance to start working.

Diplopia (or “Double Vision”) An eye problem in which you see two images of a single object. It may be present when only one eye is open (monocular) or disappear when either eye is closed (binocular). Diplopia is a common symptom of MS, and it occurs because of damage to the optic nerve.

Disease-Modifying Therapies (DMTs) Drugs designed to reduce new relapses, delay progression of disability, and limit new CNS inflammation in people with MS. Although there are multiple DMTs that have been approved by the U.S. Food and Drug Administration (FDA) for use in MS, these drugs generally work by reducing inflammation in nerve cells in the CNS.

Dysarthria A speech disorder caused by neuromuscular impairment and resulting in disturbances in motor control of the muscles used in speech. It’s believed the demyelinating lesions in MS may result in spasticity, weakness, slowness, or ataxic incoordination of the lips, tongue, mandible, soft palate, vocal cords, and diaphragm, causing this speech impairment.

Dysphagia (Difficulty Swallowing) A condition that may occur in people with MS, leading to difficulty in eating solid foods or liquids, frequent throat clearing during eating or drinking, a feeling that food is stuck in the throat, or coughing or a choking sensation when eating or drinking. It’s the result of nerve damage within the muscles that control swallowing.

Epstein-Barr Virus (EBV) A virus believed to be a possible cause or trigger for MS. Although the exact cause of MS remains unknown, researchers suggest an infectious agent may be involved in its development. Studies have found that antibodies (immune proteins that indicate a person has been exposed to a given virus) to EBV are significantly higher in people who eventually develop MS than in those who don’t. Other research has noted that people with a specific immune-related gene and high levels of antibodies to EBV in their blood are 9 times more likely to develop MS than others.

Evoked Potentials A test that measures the speed of nerve messages along sensory nerves to the brain, which can be detected on your scalp using electrodes attached with sticky pads. It’s sometimes used in the diagnosis of MS, because nerve damage can slow down the transmission of nerve signals. Evoked potential tests can indicate nerve pathways that are damaged prior to the onset of MS symptoms.

Exacerbation An occurrence of new symptoms or the worsening of old symptoms that may also be referred to as a relapse, attack, or flare-up. Exacerbations can be very mild, or severe enough to interfere with a person's ability to perform day-to-day activities.

Expanded Disability Status Scale (EDSS) The Kurtzke Expanded Disability Status Scale is a modified version of the Kurtzke Disability Status Scale that was first developed in the 1950s as a way to measure disability in people with MS.

Foot Drop (or Drop Foot) A symptom of MS caused by weakness in the ankle or disruption in the nerve pathway between the legs and the brain, making it difficult to lift the front of the foot to the correct angle during walking. If you have foot drop, your foot hangs down and may catch or drag along the ground, resulting in trips and falls. Foot drop can be managed with an AFO or other treatments.

Hematopoietic Stem Cell Transplantation (HSCT) A procedure designed to “reboot” the immune system, the National MS Society says, using hematopoietic (blood cell–producing) stem cells derived from a person’s own bone marrow or blood. If your doctor recommends HSCT, you’ll undergo a chemotherapy regimen before these cells are reintroduced to the body via IV injection, where they will migrate to your bone marrow to rebuild the immune system.

John Cunningham (JC) Virus A common infection completely unrelated to MS that is found in as many as 90 percent of people, according to the UK's MS Trust. JC virus has no symptoms and is normally controlled by the immune system. However, if your immune system is weakened, the JC virus can reactivate, causing potentially fatal inflammation and damage to the brain known as progressive multifocal leukoencephalopathy (PML). Certain MS disease-modifying therapies have been linked with increased risk for PML.

Lhermitte’s Sign An electric shock-like sensation experienced by some with MS when the neck is moved in a particular way. The sensation can travel down to the spine, arms, and legs.

Lesion (or Plaque) Refers to an area of damage or scarring (sclerosis) in the CNS caused by inflammation in MS. These lesions can be spotted on an MRI scan, with active lesions appearing as white patches. With regular MRIs, a neurologist can tell how active your MS is.

Lumbar Puncture (or Spinal Tap) A procedure used for the collection of cerebrospinal fluid (CSF), sometimes done to help diagnose MS. For this procedure, your doctor will ask you to lie on your side or bend forward while seated, before cleansing an area of your lower back and injecting a local anesthetic. He will then insert a hollow needle and extract a small amount of spinal fluid using a syringe.

Magnetic Resonance Imaging (MRI) The diagnostic tool that currently offers the most sensitive noninvasive way of imaging the brain, spinal cord, or other areas of the body, according to the National MS Society. It’s the preferred imaging method for diagnosis of MS and to monitor the course of the disease. MRI uses magnetic fields and radio waves to measure the relative water content in tissues, which is notable in MS because the layer of myelin that protects nerve cell fibers is fatty and repels water. In areas where myelin has been damaged by MS, fat is stripped away and the tissue holds more water. This shows up on an MRI as a bright white spot or darkened area, depending on how the images are made.

McDonald Criteria A guidance used in the diagnosis of MS, authored by an international panel of experts on the condition, originally in 2010. The guidance was updated in 2017. Among the key changes: advising for the use of brain MRI as part of the diagnostic process.

MS Hug A common symptom of MS. If you experience the MS hug, you may feel like you have a tight band around your chest or ribs, or pressure on one side of your torso. Some people find that it is painful to breathe. The MS hug can last for seconds, minutes, hours, or even longer.

MS Prodrome A prodrome is an early stage of signs or symptoms that happens before the onset of the typical symptoms. Many experts believe that some people who go on to be diagnosed with MS experience a prodrome, evidenced by their increased healthcare use during the 5 to 10 years prior to the first demyelinating (causing the loss or destruction of myelin in nerve tissue) event.

Myelin A substance rich in lipids (fatty substances) and proteins that helps form the myelin sheath. In MS, particularly relapsing-remitting MS, an abnormal immune response produces inflammation in the CNS, effectively attacking the myelin in the cells.

Myelin Sheath An insulating layer of fatty substances and proteins that forms around the nerves in body, including those in the CNS. It allows electrical impulses to transmit quickly and efficiently along the nerve cells, but these impulses can be slowed if the sheath is damaged, causing MS.

Neurodegeneration Refers to the process by which the myelin sheath of cells in the CNS is damaged in MS. It’s believed to be a major contributor to neurological disability in the condition, and may be the reason immune modulation treatments (disease-modifying therapy) are generally less effective in the progressive MS than in the relapsing-remitting MS.

Neurologist The “point person” for monitoring your MS treatment and managing MS symptoms. This specialist typically focuses on conditions affecting the CNS.

Neuropathic Pain A type of pain common in MS that results from changes or damage to the myelin sheath and the axons, or nerve fibers, it normally covers. MS-caused neuropathic pain may be chronic, intermittent, or occur only in response to a stimulus.

Neuropsychologist A specialist you may be referred to who helps you manage the cognitive effects of MS. Neuropsychological testing (or testing of the functioning of your brain) involves identifying memory or learning difficulties associated with MS. Cognitive rehabilitation may improve functioning.

Nociceptive Pain Caused by damage to muscles and joints, it can be either acute or chronic, and may not result from MS itself, but be caused by changes in posture or walking or the overuse of assistive devices in those with the condition.

Nystagmus A common eye abnormality in MS, it’s characterized by involuntary, rhythmic, back-and-forth motion of the eyeball, either horizontally or vertically. For those with nystagmus, the perception of the rhythmic movement of the surrounding stationary world (oscillopsia) can be disorienting and disabling.

Oligoclonal Bands (OCBs) Immunoglobulins, or proteins, that collect in blood plasma or cerebrospinal fluid (CSF). Although not every person with MS has OCBs, their presence can support a diagnosis of MS. Having OCBs is generally associated with a younger age of MS onset and a poorer prognosis.

Optic Neuritis An inflammatory condition that damages the optic nerve, a bundle of nerve fibers that transmits visual information from your eye to your brain, causing pain and temporary vision loss in one eye. It’s been linked with nerve damage resulting from MS, and may be among the first symptoms a person with the condition experiences.

Pseudobulbar Affect (PBA) A neurologic effect experienced by roughly 10 percent of people with MS as well as some with Parkinson’s disease or amyotrophic lateral sclerosis (ALS), according to the Multiple Sclerosis Association of America (MSAA). It’s characterized by sudden, uncontrollable expressions of laughter or crying without an obvious cause, which can be distressing as well as embarrassing to those who experience it. PBA is believed to be a mood disorder related to the disruption of nerve impulses in the CNS, but it’s different from depression, which is also common in MS.

Pseudoexacerbation A temporary worsening of symptoms without actual myelin inflammation or damage. It is often triggered by other illnesses or infection, exercise, a warm environment, depression, exhaustion, and stress. Urinary tract infection (UTI) is the most common type of infection to cause a pseudoexacerbation.

Radiologically Isolated Syndrome (RIS) People with RIS have brain abnormalities similar to those seen in people with multiple sclerosis (as viewed on an MRI) but typically without any symptoms. Diagnosis of RIS often happens when a person is getting an MRI as part of a medical work-up for an unrelated condition, such as a head injury or migraine.

Sclerosis A general hardening of the body tissue. The term “multiple sclerosis” refers to the multiple areas of scar tissue — often called “lesions” — that develop along affected nerve fibers and that are visible in MRI scans.

Spasticity A symptom of MS that causes your muscles to feel stiff, heavy, or difficult to move. When a muscle spasms, you’ll experience a sudden stiffening that may cause a limb to jerk. This may be painful.

Trigeminal Neuralgia (or Tic Douloureux) A type of neuropathic pain that occurs on the face (usually on one side only). It’s a known symptom of MS, and you may experience it in your cheek; upper or lower jaw; inside the mouth; or in the area around your eyes, ears, or forehead. In MS, it’s typically caused by damage to the myelin sheath around the trigeminal nerve, which among other functions controls the muscles used in chewing. The condition is triggered by everyday activities, like tensing facial muscles while shaving or when chewing.

Vertigo An intense sensation of the surrounding environment spinning around one. In MS, vertigo is typically caused by growth of an existing lesion or development of a new lesion on the brain stem or cerebellum, the area in the brain that controls balance. It can also be a symptom of a problem with the inner ear, or it can be side effect of medication used to treat MS or other health conditions you may have.