I'm sceptical too, this looks and sounds more like chronic overgrooming. I would demand the skin scrape, you need to know if you and Drum are at risk.
I have one who has balded the exact same spot, but to varying degrees, for years. The fur is short and feels spiky because he's constantly breaking off the strands which leaves it feeling like stubble. He does have a mild flea allergy which may have started the habit, but he also suffers from separation anxiety when I'm away, as his flank and belly are always much worse when we get back from holiday.
Sammy also overgroomed before we got him, and his patch looked exactly like Bass's. His was diet related. He can't have cereal or it turns him into a pussychopath and the overgrooming followed this. He had stripped his back legs and flanks almost bare, poor thing.
Daktarin Gold is a very good place to start as it has itch inhibitors as well as the anti-fungal.
I use a generic hydrocortizone ointment on Beau's belly when he's feeling the itch which does stop him in his tracks. I also wipe a little Grannicks bitter apple spray on his flank to break the habit, and for a while all this works until he gets a flea bite or his stress levels go up again.
I will say this, there is one vet at my practice I refuse to see because she does this - guesses and administers expensive "could be" medications rather than testing so you have to keep going back and back. She sent OH home with a £23 bag of prescription food for Pursley because he mentioned she had vomited once or twice recently, when all she had was a hairball. I took it back and complained.
Sadly they're not all brilliant.
Oh and they need to use the correct UV light. Different frequencies show different things.
