Michael Jackson claims he has vitiligo (sp?). Vitiligo is a real disease.
My boss has it and she is white. It is an auto-immune condition in which your body begins to attack your pigment cells. It is distantly related to such conditions as lupus.
There are three legitimate treatments for the disease, skin bleaching, pills that stimulate pigment cell growth and makeup. The pills are fairly risky, bleaching is the safest and most effective treatment if you are concerned about the appearance of blotchy skin. It also depends on how far the condition has progressed, my boss just uses some very good makeup to even her skin tone.
Michael Jackson has some serious issues, however if he has this disease it could really effect is self esteem.
Of course what he has done to his nose beats me, he is starting to look like a Roswell Alien.