What is a pseudo-exacerbation in multiple sclerosis (MS)?

A virus can cause old multiple sclerosis (MS) symptoms to resurface and make you feel like you are in an exacerbation. This is commonly called a "pseudo-exacerbation." In the hospital, we often see older people without MS who look like they are having a stroke, when all they have is a urinary tract infection. The same is true with MS patients who may look like they are having an exacerbation (relapse) but are really not. Sometimes, you may notice that older MS symptoms seem to resurface when you are tired or overheated. This also does not mean you are having an MS relapse. You may be experiencing Uhtoff's phenomenon, where heat causes older MS symptoms to resurface. A true MS relapse usually lasts for weeks to months before improving.