In the "Real World"
Usually abbreviated as "MS", Multiple Sclerosis is a disease of the central nervous system and spinal cord that results in damage to the myelin cells around the cord. This can lead to a variety of "attacks" or "episodes", including, but not limited to, partial blindness, partial or total paralysis, loss of coordination, and hampering of basic brain functions.
There are 4 types of MS: relapsing remitting, secondary progressive, primary progressive, and progressive relapsing. Each type has the potential to progress to the subsequent types.
MS "attacks" can vary depending on the type. They can be of varied duration and sometimes there can be months or even years between them
There is currently no known cure for MS. There are treatments available, designed to limit the severity and frequency of attacks, and to assist in the restoration of function lost after an attack. While MS is not necessarily a fatal disease--for most patients the average time between diagnosis and death is 30 years--there is increased risk of death due to the increasing disabilities that the disease can create.
On The West Wing
President Josiah Bartlet was diagnosed with a relapsing/remitting course of MS approximately 6 years prior to being elected President in 1998. While he initially concealed his illness from all but a small, select group of people, including his wife, brother, and three daughters, as well as his first Vice President John Hoynes, JCS chairman Percy Fitzwallace, and a few others, he revealed it over the course of seasons one and two, first informing Leo McGarry in the season 1 episode He Shall, from Time to Time. An anesthesiologist at George Washington Medical Center was told in the season 2 episode In the Shadow of Two Gunmen (Part I), as a medical necessity after the President was shot. As the season progressed, the President told his senior staff one by one about his illness, in order to gain their assistance in planning the eventual public revelation of his illness, starting with Toby Ziegler. At the climax of season 2, the President made his illness public, and was then asked in a major press conference if he would run for President again, leaving the question to be the season 2 ending cliffhanger.
The revelation of the illness became a major plot point in several episodes of season 3. A congressional investigation took place in which several members of the senior staff were called on to testify under oath. The investigation was ended after the President agreed to accept a Congressional censure in order to spare Leo the embarassment of revealing a minor relapse of his alcoholism that occured at the height of President Bartlet's first campaign, while the candidate was experiencing an MS episode. The President's wife, Abigail Bartlet, also surrendered her medical license voluntarily in order to avoid prosecution for breaking medical ethics rules by treating her husband herself.
In season 4, the President suffered a mild episode during the 2002 Presidential election, resulting in partial blindness and loss of use of his right hand temporarily. He apparently recovered from the episode with few adverse effects.
In season 5, during the episode Abu el Banat, it is revealed that the President has discussed the idea of assisted suicide with his family should his disease progress to the point where he is completely incapacitated, and that they decided against it.
In season 6, Leo reveals to CJ Cregg after she is promoted to White House Chief of Staff that he would play regular games of chess with the President as a way of determining how much the President's higher brain functions are affected by his disease. CJ continues this practice despite her lack of knowledge of the game by bringing in a member of the President's sub-cabinet who is also an expert chess player to assist her. While preparing for a summit with the Chinese premier, the President began to experience symptoms of another episode, and, while en route to China, he was overcome by near total paralysis. He managed to complete the summit successfully from a wheelchair, but he paid a heavy price for it as he suffered serious physical impairment for weeks afterward.
Throughout the rest of season 6 and for most of the season 7 episodes that he appeared in, the President retained most of his physical functionality but usually walked with the assistance of a cane. Understandably, throughout the series, the condition was only worse or highlighted when it served some purpose in the storyline.