Weakness of the lower extremities (legs).

Paralysis of both lower extremities (legs).

Partial or incomplete paralysis of a part of the body.

A spontaneously occurring sensation of burning, prickling, tingling, or creeping on the skin that may or may not be associated with any physical findings on neurological examination.

An inactive, non-drug compound that is designed to look just like the test drug. It is administered to control group subjects in double-blind clinical trials (in which neither the researchers nor the subjects know who is receiving the drug and who is receiving the placebo) as a means of assessing the benefits and liabilities of the test drug taken by experimental group subjects.

An apparently beneficial result of therapy that occurs because of the patient's expectation that the therapy will help.

Damaged area in the brain or spinal cord caused by demyelination (also called lesion or sclerosis).

Safety category for pregnant women considering or taking medication. This category means that when the medication was administered to pregnant animals, there was no detectable harm to the fetus; these studies were not done in women. Because animal studies are not predictive of human response, Pregnancy Category B medications should be used during pregnancy only if clearly needed.

Safety category for pregnant women considering or taking medication. This category means that when the medication was administered to pregnant animals, there was some harm done to the fetus. Category C medication should be used only if clearly needed (that is, if you and your doctor determine that the benefits outweigh the risks).

Safety category for pregnant women considering or taking medication. This category means that when the medication was administered to pregnant women there was evidence of risk to the fetus. Category D medication should be used only if clearly needed (that is, if the drug is needed in a life-threatening situation or safer drugs cannot be used or are not effective).

A less common form of MS than the relapsing-remitting form. PPMS makes up approximately 10% of all people with MS and is characterized by a slow but nearly continuous worsening of disease.

A very rare and potentially fatal disease of the central nervous system (CNS).

The rarest form of MS that affects approximately 5% of all diagnosed patients. People with PRMS may go through a steady worsening of their condition after being diagnosed. They may also experience clear, severe relapses with or without complete recovery.

A temporary aggravation of disease symptoms, resulting from an elevation in body temperature or other stressor (eg, an infection, severe fatigue, or constipation). The exacerbation disappears once the stressor is removed. A pseudo exacerbation indicates symptom flare-up rather than new disease activity.