If that wasn't caused by rubbing himself on a round feeder or something else, as has been suggested, it's possible he has neck threadworms, a/k/a hairworms, a/k/a Onchocerca worms <--- thanks to Midge fly bites which also produce sweet itch.
You might consider asking your vet about double-dosing him with PURE Ivermectin. You can buy 1.87% Ivermectin at TSC.
I was a naysayer that the skin outbreaks on two of my horses faces, neck, crest, belly were caused by hairworms, but I wormed anyway and that's what it was - hairworms.
The way you know if it is hairworms causing the skin rashes, is that the rash will get much worse after worming before it gets better. That is because the microfiliae are dying off.
Again, ask your vet's opinion, but I'll bet $$$ he/she will say "no, it's just a summer heat rash." Since you deal with this every summer (when the midge flies are out in full force), you could then ask the vet to do a skin scraping to be sure.
As far as a topical, you could try mixing some Fur-All or Corona cream with some Desitin to help the healing process