In my fantasy world, there is a King afflicted with leprosy. He is in his mid-to-late 40's, and has recently been diagnosed with this horrible disease. What are the disadvantages (and advantages, if any) of ruling with this affliction? Could he expose himself to others if he wore thick layers of clothing or a mask? What might his vassals think? This is a low-fantasy world, heavily based on 12th-14th century Europe.
One example from history is Baldwin IV of Jerusalem, who ruled Jerusalem in 1174.
He was diagnosed with leprosy when he was a child.
He was crowned at 13 and reigned for 11 years before his death.
Because he got the disease at a young age, he never married and had no heir.
Instead he appointed his nephew as king.
He had to be careful in battle while leading his troops, since he wouldn't be able to feel wounds. Even something like a saddle sore could give him a lot of problems, since he wouldn't know it was starting, and it could get infected.
Can't think of any real advantages
Others have already covered all the disadvantages I can think of so I'll just focus on the advantages.
1) You get to choose your heir. Many times in history the son of the king really wasn't suited to the throne.
2) It would be a good morale booster. "The king is sick and he's still out here fighting with us!"