Suggest Treatment For White Spots On Knee And Feet

My son is 7 years old. He has some white spots on his knees and tops of feet. Over the last year, they have spread and now are on his elbows and a few on the back of his neck. The doctor told us several months ago it was a fungul thing and to put selsun blue shampoo on htem at nighttime and it would go away. It has not gone away. He also stated it was very contagious, but none of our other 3 children have developed these spots.