The charmingly named 'lethal midline granuloma' (now more commonly, but less dramatically, known as '
polymorphic reticulosis'), is one of the medical conditions from which one can suffer. It isn't a disease; rather, it's a leprosy-like condition which can develop through infection or trauma to the nasal region and sinuses. It strikes most often at those who abuse
cocaine and is a very good reason not to put things up your nose. The threat of it can also be used to prevent your children from becoming fixated with
bogies.
It is characterised by "progressive relentless ulcerations and necrosis of midfacial structures", which essentially means that it eats your face off from the inside. Or your nose, more precisely, causing "massive, progressive osteocartilaginous necrosis of the sinonasal tract and palate". This is fully as bad as it sounds.
It can usually be limited with radiotherapy and also by removing the cause of the trauma or infection; the drastic effects cannot be reversed and require extensive reconstructive surgery. If it is not treated the necrosis carries on until you are dead, which is why it's called 'lethal midline granuloma' and not just 'midline granuloma'.
Sources:
http://www.bcm.tmc.edu/oto/grand/72392.html
http://www.cgmh.com.tw/paper/23-2-6.htm