Thank you for the photos of Oscar's bald patch. I have had a look at this this morning (since they did arrive very late last night after I had gone to sleep), but the good news is that it doesn't look like you are facing a fungal infection or mite based infestation. That said, based on the appearance of the bald spot, its being wet (which is him licking it due to irritation), the twitching (another sign that this is itchy), and the thinning of the hair, it appears that Oscar is caught in an allergy based skin reaction that is causing overgrooming of the lesion.
Now allergies can arise due to anything in the environment (ie pollens, dietary proteins, flea saliva, laundry soap, carpet powder, etc). Still if he is only overgrooming his back, flea saliva will be the first culprit to rule out. Therefore, if you have not treated him for fleas in the past 4 weeks with a good quality product, then consider doing so now.
Of course, if you have changed his diet or know he is being exposed to contact allergens (like laundry soap, carpet powder, etc), then you will want to address these as well.
In regards ***** ***** to soothe the itch, reduce his overgrooming the area, and at the same time rule out allergic skin disease (flea saliva induced or environmental allergen), you can consider treating him with an anti-histamine. Anti-histamines can settle allergic skin reactions in early stages or mild cases since the skin irritation is an allergic response. Typically in these cases, we will use Piriton for these wee ones (ie 1-2mg or 1/4 – 1/2 tablet of a 4mg Piriton tablet up to twice daily). Do note that while anti-histamines will break that itchiness cycle and give his skin the chance it needs to settle, it can make kitties drowsy. Therefore, we always keep the dose low and if he were to be drowsy on this, then we'd reduce the dose to once daily for him. And of course, this medication shouldn't be used if your kitty has any pre-existing conditions or are on any other medication without speaking to your vet. That all said, if you treat him with this and he doesn't settle or his irritation is very severe ( a wee concern here), then he may require a short course of a steroids from his vet to allay the allergic skin response and associated itchiness.
Otherwise, besides your salt water bathing (which is good to keep secondary infection away), you will need to consider protecting this area from his grooming. To do so, consider placing a buster collar to keep him from licking. These can be purchased from pet stores and the vet. Otherwise, if the area is high enough, you can try covering te area with a long baby t-shirt (ideally with an elastic waist). Do no be tempted to bandage the area, since that would lock in moisture and leave the skin to fester.
Overall, this bald patch is due to overgrooming being triggered by local skin irritation. Your salt water bathing is good but we need to prevent him from licking while trying to settle his skin with an antihistamine. If you this for a few days but he still seems itchy, then he may need stronger anti-allergy treatment. If that is the case, then you would want to speak to his vet about a short course of steroids to allay the itch and allow his skin to settle.
I hope this information is helpful.
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All the best,
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