Hi guys .. thank you all for your replies, they have been of great help.
PolarPeak, a couple of days ago we actually found one live adult flea and what looked like flea droppings near the affected areas. We frequent a dog park so it is possible that he might have caught it from there. But thank you for questioning the matter and looking at other possibilities, skin problems like these may be due to numerous things of course.
After commencing his medication, our sibe's skin is already improving and he is no longer trying to get at the patches. After reading all the replies and also other threads on this, we have decided to go with Advantage + Interceptor Spectrum to cover his worms. Hopefully after changing his treatment it will lessen the likelihood of this happening again !!